Impact on Combustion and Emissions of Jet Fuel As Additive in Diesel Engine Fueled with Blends of Petrol Diesel, Renewable Diesel and Waste Cooking Oil Biodiesel

energies

Article Impact on Combustion and Emissions of Jet Fuel as Additive in Diesel Engine Fueled with Blends of Petrol Diesel, Renewable Diesel and Waste Cooking Oil Biodiesel

Giancarlo Chiatti, Ornella Chiavola * and Fulvio Palmieri Engineering Department, ROMA TRE University, via della vasca navale, 79, 00146 Rome, Italy * Correspondence: [email protected]

Received: 31 May 2019; Accepted: 26 June 2019; Published: 28 June 2019

Abstract: This study is devoted to investigating the potential use of Jet A in blend along with biodiesel from waste cooking oil, petrol diesel, and renewable diesel. Biodiesel use allows for reducing carbon monoxide (CO), unburned hydrocarbons (HC), and soot due to the oxygen contained in the fuel. The drawbacks in its use are related to the low volatility and high viscosity of vegetable oil that cause difficulties in fuel atomization and in its mixing with air. Moreover, an increased amount of NOx emission was observed. The aim of the experimentation is to evaluate the ability of Jet A of enhancing the combustion process and pollutant emissions of a diesel engine, thus overcoming the difficulties in biodiesel usage (high viscosity, poor cold weather performance, compatibility with diesel engine equipment) and then increasing the renewable fuel percentage in the fuel. Testing was carried out on a small displacement common rail diesel engine. Hardware and ECU setting were not modified in order to let the engine be ready to operate with different and exchangeable fuels. The effect on pollutant emissions of a variation of the amount of Jet A and biodiesel in the fuel is investigated, while accounting for the engine speed value.

Keywords: diesel engine; emissions; biodiesel; waste cooking oil; renewable diesel; jet fuel

1. Introduction The exhaust emissions of internal combustion engines significantly contribute to the environmental degradation of the urban area. Environmental sustainability, economic, and social concerns have motivated researchers to examine and evaluate the performance of alternative fuels e.g., renewable diesel and biodiesel. Renewable diesel, which is also called ‘green diesel’, is a branched paraffin-based, completely deoxygenated fuel that is produced, starting from biological sources, through a hydrogenation reaction where the source reacts with hydrogen to obtain a liquid hydrocarbon fuel. The main advantage of this fuel is the full compatibility with petroleum diesel [1,2]. Research activity on the use of renewable diesel used in blends with petrol diesel showed a decrease in carbon monoxide (CO) and unburned hydrocarbons (HC) emissions [3] and a degradation of the cold properties of green diesel, which was caused by the high content of n-paraffin in the fuel [4]. Biodiesel is a diesel fuel that consists of fatty acid methyl esters, which are generally produced trough a transesterification process of vegetable oils and animal fats. It can be obtained, starting from many sources and, among them, very promising is the fuel obtained from oilseed rape sources that are unsuitable for consumption by humans and animals [5,6] and from mixtures of waste cooking oils (WCO). The use of WCO allows for eliminating the drawback of its disposal; moreover, it is less expensive than virgin oil [7]. Biodiesel from WCO has highlighted its attitude to be used as biofuel in

Energies 2019, 12, 2488; doi:10.3390/en12132488 www.mdpi.com/journal/energies Energies 2019, 12, 2488 2 of 14 diesel engines [8,9]. Studies regarding vegetable oil based fuels revealed that the use of neat biodiesel or high percentage of biodiesel blends cannot be employed in diesel engines, since they are responsible for some problems in unmodified diesel engines during their operation due to the high viscosity and density of vegetable oils and to their flow properties and poor volatility. Many engine manufactures approve of biodiesel use only up to a fixed limit. Several investigations studies have highlighted the role of biodiesel on engine emission characteristics and performance. The oxygen in the fuel results in HC, CO, and particulate matter (PM) reduction; a general increase of nitrogen oxides (NOx) emission is also observed, due to the higher oxygen available in biodiesel. However, biodiesel has a lower caloric value as regarding diesel oil, which thus results in engine power losses when it is blended with conventional diesel fuel [10–14]. The use of an additive could solve the problems related to the use of high biodiesel ratios in blends during the operation in an unmodified engine. Among possible additives, the use of jet fuels, as characterized by lower density and viscosity and better flow properties, could be a very attractive solution. Injection and mixing could be improved by blending biodiesel with aviation fuels. The lower cetane number of these fuels may cause longer ignition delay, but this issue could be balanced by its lower distillation temperature that shortens the ignition delay. Kerosene use in direct injection diesel engines started at the end of 1980s when by NATO nations introduced the single fuel concept, who decided to use a specific fuel to supply all land based military aircraft and vehicles that aimed at simplifying the logistic chain for petroleum by-products [15,16]. F-34 (JP-8) military jet kerosene was selected as the single fuel; it has the same specifications of the F-35 (Jet A), except for those that are related to the use of additives that are used to inhibit system icing and to face with corrosion and thermal stability [17]. JP-8 does not have cetane number specifications; investigations on the effects of the variability of cetane have highlighted that the cetane index varies in the range 31.8–56, with a mean value of 43.4, with a great impact on ignition delay, premixed combustion phase, and resulting in large variation of pressure rise rates [16]. Only few investigations have been performed on the use of biodiesel-kerosene blends in compression ignition engines, even if there are many studies on the combustion process and pollutant emissions of different type of biodiesel fuels used in blends with petrol diesel. Arkoudeas et al. [17] investigated the pollutant emissions from a stationary single cylinder diesel engine in which blends of biodiesels from sunflower and olive oils and JP-8 are used. The use of biodiesel resulted in a reduction of PM and in the limited change of NOx. The reduction in particulate emissions was the most related to high loads conditions, while the reduction was marginal at low loads. Reference [18] is devoted to present a study on a the use of blends of biodiesel and kerosene in a direct injection diesel engine. The authors found that the percentage of 20% kerosene and 80% biodiesel causes a reduction of the pollutant emissions as regards diesel fuel. Llamas et al. [19] used Jet A1 that was blended with bio kerosene; their investigations concluded that biodiesel could be used to partially substitute fossil jet fuels. Chen et al. [20] investigated the emissions from a single cylinder diesel engine that was fueled with kerosene. Such a fuel improved the indicated thermal efficiency and reduced the soot emissions; nitrogen oxide emissions did not have a relevant variation. Aydin et al. [21] tested biodiesel-kerosene blends in a single cylinder diesel engine; kerosene was used to improve biodiesel properties, thus to approach diesel ones. Reference [22] presents an experimental evaluation on the impact of substituting a fraction of fuel by alternative to fossil oils. Gowdagiri et al. [23] studied the impact of jet fuels (JP-5, Jet A), petroleum diesel, and alternative diesel (hydroprocessed algae diesel, hydroprocessed camelina) on ignition delay, emissions, and fuel consumption of a compression ignition engine. The results indicate the relation between fuel properties and engine performance. Rothamer et al. [24] analyzed the ignition delay of diesel and jet fuels in a heavy-duty diesel engine. Reference [25] is devoted to present study on the use of a high percentage of biodiesel in a unmodified diesel engine. Two blends were prepared, in which 80% biodiesel was contained; in one, it was added to 20% of kerosene, on the other, it was blended with kerosene (10%) and diesel fuel (10%). The obtained results Energies 2019, 12, 2488 3 of 14 highlight a reduction of density and viscosity of the blend in which kerosene is used as an additive to biodiesel. Even though it emerges that some research activity has been performed regarding jet fuels usage in compression ignition engines, studies are limited and most of published data are related to tests at specific value of engine speed, in which biodiesel–kerosene blends are used. Therefore, the necessity of further studies arises. The topic of this work is to investigate the impact on combustion and emission characteristics of Jet A percentage in a blend containing biodiesel from WCO and diesel fuel. Aiming at increasing the percentage of renewable fuel, instead of petrol diesel, it was used an innovative fuel (diesel +), in which a fraction of renewable diesel is contained. Previous research activity was devoted to analyze the combustion process and emission characteristics of a diesel engine fuelled with biodiesel from waste cooking oil in blends of petrol diesel and renewable diesel [26]. The results established that the use of a blend of diesel + and biodiesel from WCO enhances PM, HC, and CO emissions in the exhaust as regards petrol diesel; a moderate increase characterizes nitrogen oxides emission. The objective of this work is to present the results of an experimentation, in which Jet A was mixed with diesel + and biodiesel from WCO with the objective of evaluating whether the aviation fuel use allows for the reduction of the typical drawbacks of using biodiesel and the enhancement of the exhaust emissions.

2. Materials and Methods

2.1. Experimental Set-Up A Kohler naturally-aspirated two-cylinder, water-cooled, common rail diesel engine is the engine used in the present experimentation; the injection pump delivers fuel with a maximum pressure of up to 80 MPa. The electronically controlled injector has ﬁve holes, the diameter of each being equal to 0.123 mm. Table1 reports the engine’s main speciﬁcations. It was installed in the test cell of the ROMA TRE University—Engineering Department. The engine was connected to the Siemens 1PH7 asynchronous motor and it was instrumented for the complete monitoring of its operation.

Table 1. Engine main data.

Engine Type LDW442CRS Naturally Aspirated Cylinders 2 Bore 68 mm Stroke 60.6 mm Displacement 440 cm3 Compression ratio 20:1 Maximum torque 21 Nm @ 2000 rpm Maximum power 8.5 kW @ 4400 rpm

HBM T12 was used for torque measurement. The AVL Fuel Balance model 733 was used for supplying the fuel and measuring the consumption, with an accuracy of 0.12%. Pressure transducers were placed in different positions in the intake and exhaust systems. A piezoelectric transducer (AVL GU13P) was installed in the in-cylinder for pressure measurement; a crank encoder was used for recording the crank-angle resolved pressure. AVL Indicom software was used for the data monitoring and acquisition. Further details of the experimental set up may be found in [27]. The exhaust gas composition was analyzed while using the exhaust gas analyzer Bosch BEA352. In this equipment, the HC analyzer uses a heated flame ionization detector; the CO measuring instrument uses the non-dispersive infrared detectors, the NOx analyzer uses the heated chemiluminescence detector. The accuracies of HC, CO, and NO are 1 ppm vol, 0.001% vol, and 1ppm vol, respectively. The size distribution of particulate matter was measured through Cambustion DMS500, which has proven to be characterized by good correlation with regulation compliant systems [28]. The instrument has an uncertainty of about 5% in particle size measurement for particles that are smaller than 300 nm Energies 2019, 12, 2488 4 of 14 and about 10% over the full spectrum for particle number density measurement [29]. Cambustion DMS500 is a classifier column for detecting PM of size in the range 5 nm–1 µm with a resolution of 16 channels/decade. The incoming exhaust gas passes through a cyclone that is used to remove from the flow all particles larger than 1 µm. Two dilution stages are applied before the sample gas passes through a corona charger and into the classifier column: the primary dilution rate was set to 5:1; second dilution rate was set to 400:1. Once the charged particles enter the column, they are deflected toward the grounded electrometer rings by their repulsion from the high voltage rod in the center of the device. The particles charge and aerodynamic drag determine their landing position.

2.2. Fuels and Tests Different blends were tested in the experimentation: diesel + (standard ultralow sulfur diesel fuel, ULSD, with 15% by volume of renewable diesel [30]) was mixed with biodiesel from WCO and Jet A in different percentages. Renewable diesel was obtained via the EcofiningTM Process [31] from palm oil, but it may be produced, starting from a wide range of feedstocks. The process consists in subsequent reactions of decarboxylation, hydrodeoxygenation, and hydroisomerization. As the final product, a totally hydrocarbon fuel is obtained, since it does not contain oxygen, unlike traditional biodiesel. A second-generation biodiesel was used in the experimentation. It was produced from a mixture of waste cooking oils. Some of the treatments were performed to enhance the poor qualities of the initial material and let the oil become similar to a product that was obtained from refined vegetable oils. A cleaning disk separator was used in order to remove the part containing the water-soluble matter and solids. A second disk separator machine allowed for removing the water leftover. Physical deacidification and transesterification process were then performed. The resulting raw biodiesel was distilled, aiming at complying with the reference specifications of biodiesel (EN 14214). In [12], more details of the procedure may be found. Table2 lists the composition of the utilized biodiesel.

Table 2. Composition of biodiesel from waste cooking oils (WCO).

Mass Fraction Biodiesel Carbon 0.812 Hydrogen 0.065 Oxygen 0.117 Sulfur 0.006

Preliminary investigations were devoted to define the highest percentage of waste cooking oil in the blend that can be used without requiring engine hardware modification, since the compatibility of biodiesel with engine equipment limits the maximum allowable concentration in the fuel. Testing revealed that the maximum biodiesel percentage that can be tested is 40%; higher quantities of biodiesel in the blend are responsible for the degradation of the rubber hoses/seals in the fuel supply system [12]. Jet A is a kerosene-type fuel that is suitable for most jet aircraft. The fuel complies the international requirements, particularly those of the latest versions of the AFQRJOS, the British DEF STAN 91-91 standard, the ASTM D1655 standard, and the NATO F-35 specification. Table3 presents the properties of biodiesel from waste cooking oil, renewable diesel, ULSD, diesel + and Jet A.

Table 3. Renewable diesel, ULSD, diesel +, biodiesel from WCO and Jet A properties.

Property Renewable Diesel [32] ULSD Diesel + [32] Biodiesel from WCO [12] Jet A 3 density [kg/m at 15 ◦C] 780 830 840 877 801 lower heating value 44 43.1 43.2 37.1 43.4 [MJ/kg] cetane number 80 52 55 56 47 Energies 2019, 12, 2488 5 of 14

Jet A is characterized by lower viscosity, distillation temperature range, and cetane number as regards ULSD fuel; the lower density, viscosity, and surface tension cause its better atomization when compared to diesel fuel [20]. Stationary tests were performed in the entire speed range of the engine, from 2400 rpm to 3600 rpm, with a step of 300 rpm. The load value was ﬁxed at 80% as regards the torque available at the full load condition when the engine was supplied with petrol diesel; this allowed for imposing on the engine an high value of torque that was equal for all of the tested fuels. The injection strategy and settings were not modiﬁed to account for the fuel properties (details are reported in Table4).

Table 4. Injection settings.

Engine Speed Torque SOI pre SOI Main Prail [rpm] [Nm] [cad BTDC] [cad BTDC] [bar] 2400 18.2 18.5 5.9 620 2700 19.0 18.4 5.9 610 3000 17.5 15.5 6.0 610 3300 17.0 16.8 6.3 630 3600 15.2 18.1 6,7 650

The engine was allowed to run for about 10 min during the experimentation, before starting a new test, in order to consume the remaining fuel from previous testing. Once stable condition with the new fuel was obtained, measurements have begun with a speciﬁc blend. For each test, the average of the recorded data was computed, thus to reduce the engine cycle irregularities once the signals were acquired (25 cycles were used, the increase in this number did not change the feature of the trends).

3. Results The ﬁrst part of this section is devoted to analyzing the impact on combustion process and emissions characteristics of Jet A percentage in the blends with diesel +. During the experimental tests, two blends containing 10% and 20% by volume (named DK10 and DK20, respectively) have been used and their performance is compared to those that were obtained by fueling the engine with net diesel+. The second part of this section focuses on the evaluation of the possible use of aviation fuel to reduce the typical drawback of using biodiesel (diﬃculties in atomization and mixing with air caused by its high viscosity, low volatility) and to enhance the emissions. The results obtained during the experimentation of blends in which Jet A is mixed with diesel + and biodiesel from WCO are presented.

3.1. Jet A blended with diesel + The investigation is based on the results of a previous activity on the same engine, which pointed out how using diesel + on replacement of ULSD allows for a reduction of CO, HC, and soot emissions, along with an increase of NOx emission [26]. Jet A was blended with diesel +; the combustion and pollutant emissions were analyzed with the aim of evaluating the impact of diﬀerent percentages of Jet A on diesel + behaviour as a function of engine speed condition. Figure1 shows CO and HC emissions from diesel + used net or blended with 10% and 20% by the volume of Jet A. The air fuel ratio and the available temperature in the cylinder are the parameters that primarily govern the emission. Data related to carbon monoxide exhibit a reduction of the emission as the percentage of Jet A in the blend increases, especially at low engine speed values. This behavior is caused by the high volatility of Jet A, which promotes the combustion; at higher engine speed, such an eﬀect is balanced by the cetane number of the aviation fuel and its longer ignition delay, which promote CO emission. The blending of Jet A is responsible for an increase of hydrocarbon emissions, except for lowest values of speed when DK20 is used; this feature could be caused by the longer ignition delay of Energies 2019, 12, x FOR PEER REVIEW 6 of 13

0.0450,045 25 Energies0.0400,042019, 12, 2488 6 of 14 20 0.0350,035

0.0300,03 15 Jet A and0.0250,025 incomplete combustion. The HC emissions are related to the locally lean and locally high rich

CO [%] CO 0.0200,02 regionEnergies of 2019 the, 12 chamber;, x FOR PEER they REVIEW are also attributed to the ﬂameHC [ppm] 10 extinction in the cold regions of the cylinder.6 of 13 0.0150,015

0.0100,01 5 0.0450,045 25 0.0050,005 0.0400,04 0 200 0.0350,035 2200 2400 2600 2800 3000 3200 3400 3600 3800 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] 0.0300,03 engine speed [rpm] 15 0.0250,025

CO [%] CO 0.0200,02

HC [ppm] 10 0.0150,015 0.0100,01 5 0.0050,005

Figure0 1. Carbon monoxide (CO) and unburned hydrocarbons0 (HC) variation with engine speed, 80% 2200 2400 2600 2800 3000 3200 3400 3600 3800 2200 2400 2600 2800 3000 3200 3400 3600 3800 load. engine speed [rpm] engine speed [rpm]

In Figure 2, the variation of NO emission as function of the engine speed is shown (NOx are expressed as NO equivalent). All of the curves present a decreasing trend as the engine speed increases. This behaviour is due to the reduction of ignition delay that is caused by the increase of gas motionFigure 1. inCarbon the chamber monoxide at higher (CO) and values unburned of engine hydrocarbons speed. Moreover, (HC) variation the withresidence engine time speed, at high Figure 1. Carbon monoxide (CO) and unburned hydrocarbons (HC) variation with engine speed, 80% temperature80% load. within the cylinder is reduced with the increase of engine speed, which resulted in a load. decrease of NOx emission. InThe Figure effect2 ,of the adding variation Jet A ofto NOthe fuel emission is a significant as function reduction of the enginein the emission, speed is especially shown (NO at lowerx are In Figure 2, the variation of NO emission as function of the engine speed is shown (NOx are expressed as NO equivalent). All of the curves present a decreasing trend as the engine speed increases. engineexpressed speed as values.NO equivalent). The primary All factors of the that curves affect present NOx formation a decreasing are the trend availability as the ofengine oxygen speed and This behaviour is due to the reduction of ignition delay that is caused by the increase of gas motion in theincreases. high combustion This behaviour temperature. is due to Boththe reduction diesel and of aviationignition fueldelay have that limitedis caused oxygen by the content increase and of the chamber at higher values of engine speed. Moreover, the residence time at high temperature within similargas motion air/fuel in the ratio; chamber for diesel at higher +, the valuesenhanced of engine portion speed. of premixed Moreover, combustion the residence at 80% time of atload high is the cylinder is reduced with the increase of engine speed, which resulted in a decrease of NOx emission. responsibletemperature for within the higher the cylindertemperature is reduced in the cylinder, with the thus increase contributing of engine to the speed, larger whichamount resulted of NOx [26].in a

decrease of NOx emission. 1000

The effect of adding Jet A900 to the fuel is a significant reduction in the emission, especially at lower

engine speed values. The primary800 factors that affect NOx formation are the availability of oxygen and

the high combustion temperature.700 Both diesel and aviation fuel have limited oxygen content and

similar air/fuel ratio; for diesel600 +, the enhanced portion of premixed combustion at 80% of load is

responsible for the higher temperatureNO [ppm] 500 in the cylinder, thus contributing to the larger amount of NOx [26].

400 1000 300 900 200 8002200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] 700

600 NO [ppm] 500 Figure400 2. NO variation with engine speed, 80% load. Figure 2. NO variation with engine speed, 80% load. 300

The effect of adding Jet A to200 the fuel is a significant reduction in the emission, especially at lower Figure 3 presents the effect2200 of Jet 2400 A 2600on the 2800 particulate 3000 3200 3400emission 3600 3800of the engine. Looking at soot engine speed values. The primary factors that affect NOx formation are the availability of oxygen concentration in the exhaust, all of the traces showengine speed an [rpm] increase in the values with the engine speed, and the high combustion temperature. Both diesel and aviation fuel have limited oxygen content accordingly with literature results on the relation between particulate emission and engine speed and similar air/fuel ratio; for diesel +, the enhanced portion of premixed combustion at 80% of load [14,33]. This behavior is to ascribe to the balance between the reduction of time available for air‐ is responsible for the higher temperature in the cylinder, thus contributing to the larger amount of mixing and combustion, which penalizes combustion completeness, and the enhancement of NOx [26]. Figure 2. NO variation with engine speed, 80% load. turbulence, which improves the combustion completeness. Figure3 presents the e ffect of Jet A on the particulate emission of the engine. Looking at soot Mixing Jet A to diesel + causes an increase of particulate emissions at lower engine speed values. concentrationFigure 3 inpresents the exhaust, the effect all of of the Jet tracesA on the show particulate an increase emission in the valuesof the engine. with the Looking engine speed,at soot This is caused by the properties of the fuels: the lower cetane of Jet A increases the ignition delay and accordinglyconcentration with in literature the exhaust, results all onof thethe relationtraces show between an increase particulate in emissionthe values and with engine the engine speed [ 14speed,,33]. the ignition occurs later than diesel +; the energy released during premixed combustion is increased, Thisaccordingly behavior with is to literature ascribe to results the balance on the between relation the between reduction particulate of time available emission for and air-mixing engine speed and resulting in higher pressure and temperature in the cylinder, according to [34]. combustion,[14,33]. This which behavior penalizes is to ascribe combustion to the completeness, balance between and the the enhancementreduction of time of turbulence, available for which air‐ improves mixing and the combustioncombustion, completeness. which penalizes combustion completeness, and the enhancement of turbulence, which improves the combustion completeness. Mixing Jet A to diesel + causes an increase of particulate emissions at lower engine speed values. This is caused by the properties of the fuels: the lower cetane of Jet A increases the ignition delay and the ignition occurs later than diesel +; the energy released during premixed combustion is increased, resulting in higher pressure and temperature in the cylinder, according to [34].

Energies 2019, 12, x FOR PEER REVIEW 7 of 13

Regarding particle size, Figure 3 shows the influence of fuel type on the mean diameter of accumulation mode as a function of engine speed. A bimodal distribution of PM size was observed for tested blends. All of the operative conditions of the engine are characterized by a predominance Energiesof accumulation2019, 12, 2488 mode as regards the nucleation one. The court mean diameter (CMD) has an average7 of 14 value around 80 nm and it not exhibit significant changes with the fuel.

3,5E+083.5X108 1,2E+021.2X102

3,0E+083.0X108 1,0E+021.0X102 2,5E+082.5X108 ] 3 1 2,0E+082.0X108 8,0E+018.0X10

1,5E+081.5X108 1 CMD [nm] CMD Ntot [N/cm Ntot 6,0E+016.0X10

1,0E+081.0X108 4,0E+014.0X101 5,0E+075.0X107

0,0E+000.0X100 2,0E+012.0X101 2200 2400 2600 2800 3000 3200 3400 3600 3800 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] engine speed [rpm]

FigureFigure 3.3. Particle number concentration andand meanmean diameterdiameter variationvariation withwith engineengine speed,speed, 80%80% load.load.

Mixing Jet A to diesel + causes an increase of particulate emissions at lower engine speed values. The combustion development was analyzed by means of the Rate of Heat Release curve, aimed This is caused by the properties of the fuels: the lower cetane of Jet A increases the ignition delay and at deeper insight into the impact of fuel properties on exhaust pollutants formation. The acquired in‐ the ignition occurs later than diesel +; the energy released during premixed combustion is increased, cylinder pressure was used to compute the heat release during the combustion. A thermodynamic resulting in higher pressure and temperature in the cylinder, according to [34]. model allowed for the computation; the instantaneous heat loss to the cylinder wall was evaluated Regarding particle size, Figure3 shows the influence of fuel type on the mean diameter of by the Woschni model [35]. accumulation mode as a function of engine speed. A bimodal distribution of PM size was observed for In this study, the injection strategy was not changed, since the aim of the research was not to tested blends. All of the operative conditions of the engine are characterized by a predominance of optimize the injection setting for the different blends, but it was to investigate the engine behaviour accumulation mode as regards the nucleation one. The court mean diameter (CMD) has an average with an unmodified ECU setting. A two‐stage injection was imposed on the engine; during tests, the value around 80 nm and it not exhibit significant changes with the fuel. shots setting was modified for each operative point, but it was not changed with the fuel type. 1 The combustion development was analyzed by means of the Rate of Heat Release curve, aimed mm3/stroke of fuel was delivered during pre‐injection; during main injection, adjustment of fuel at deeper insight into the impact of fuel properties on exhaust pollutants formation. The acquired quantity was allowed to impose the same torque value, no matter the fuel type is (Table 5 presents in-cylinder pressure was used to compute the heat release during the combustion. A thermodynamic the ECU settings for the injected fuel quantity). model allowed for the computation; the instantaneous heat loss to the cylinder wall was evaluated by the Woschni model [35]. Table 5. Injected quantity. In this study, the injection strategy was not changed, since the aim of the research was not to Engine Speed Air Mass Q pre Q main Diesel + Q pre DK10 Q Main DK20 optimize the injection setting for the different blends, but it was to investigate the engine behaviour [rpm] [kg/h] [mm3/str] [mm3/str]] [mm3/str] [mm3/str] with an2400 unmodified ECU35,0 setting. A1 two-stage injection11.9 was imposed12.0 on the engine; during11.9 tests, the shots2700 setting was38,9 modified for each1 operative point,10.3 but it was not10.7 changed with the10.6 fuel type. 1 mm33000/stroke of fuel42,7 was delivered1 during pre-injection;8.8 during main injection,9.2 adjustment9.1 of fuel quantity3300 was allowed46,5 to impose the same1 torque value,8.9 no matter the fuel8.7 type is (Table5 presents9.2 the 3600 50,4 1 8.3 8.1 8.3 ECU settings for the injected fuel quantity). Figures 4 and 5 present the Rate of Heat Release and the in‐cylinder pressure trends that were Table 5. Injected quantity. obtained for the tested fuels under a fixed value of engine speed. In Figure 4, the energizing timings of theEngine pre and Speed main injectionAir Mass are plottedQ pre as boxesQ overlapped main Diesel to theQ curves. pre DK10 Q Main DK20 It has[rpm] to be considered[kg/h] how injection[mm3/str] works:+ [mm ECU3/str]] establishes[mm the3/str] duration [mmof pre3/str]‐injection process, thus2400 to deliver 1 35,0mm3 of fuel in 1order to analyze 11.9 the curves. When 12.0 blends of diesel 11.9 + and Jet A are used,2700 the lower values 38,9 of density and 1 viscosity of 10.3 aviation fuel alter 10.7 the properties 10.6 of the blends. The unchanged3000 energizing 42,7 timings injection 1 timings cause 8.8 a longer duration 9.2 of injection, 9.1 according 3300 46,5 1 8.9 8.7 9.2 to [36]. These3600 variations are 50,4 responsible 1for a modification 8.3 of the mass 8.1 that is delivered 8.3 during pre‐ injection; during the main injection, the amount of delivered fuel is established by ECU to guarantee the required torque value. The fuel properties also affect spray penetration, velocity, and angle [36]. Figures4 and5 present the Rate of Heat Release and the in-cylinder pressure trends that were obtained for the tested fuels under a fixed value of engine speed. In Figure4, the energizing timings of the pre and main injection are plotted as boxes overlapped to the curves. Energies 2019, 12, x FOR PEER REVIEW 8 of 13 Energies 2019, 12, x FOR PEER REVIEW 8 of 13 When DK10 is used, Jet A in pre‐injected fuel delays the first peak of heat release curve. A larger When DK10 is used, Jet A in pre‐injected fuel delays the first peak of heat release curve. A larger amount of heat is released before TDC as regards diesel +. The high temperature allows for a fast amount of heat is released before TDC as regards diesel +. The high temperature allows for a fast evaporation of diesel + in the blend, thus promoting the oxidation reactions. The lower cetane number evaporation of diesel + in the blend, thus promoting the oxidation reactions. The lower cetane number characterizing Jet A causes an extension of the heat release curve that is moved towards the expansion characterizing Jet A causes an extension of the heat release curve that is moved towards the expansion stroke. When DK20 is used, the heat release released before TDC is increased as regards diesel+, the stroke. When DK20 is used, the heat release released before TDC is increased as regards diesel+, the effect of cetane number on moving the combustion towards the expansion stroke is more evident as effect of cetane number on moving the combustion towards the expansion stroke is more evident as regards the DK10 blend. Mixing Jet A in the blend makes the subsequent combustion phases more regardsEnergies the2019 DK10, 12, 2488 blend. Mixing Jet A in the blend makes the subsequent combustion phases8 of 14 more contiguous, as in‐cylinder pressure curves show. contiguous, as in‐cylinder pressure curves show. 80 80 70 70 deg] 3 60 deg] 3 60 50 50 40 40 30 30 20 20 Rate of Heat Release [kJ/m Release Heat of Rate 10 Rate of Heat Release [kJ/m Release Heat of Rate 10 pre main 0 pre main 0 -20-100 10203040 -20-100crank angle 10203040 [deg] crank angle [deg]

Figure 4. Rates of heat release at 3300 rpm, 80% load. FigureFigure 4. 4.RatesRates of of heat heat release release at 33003300 rpm, rpm, 80% 80% load. load.

80 80 70 70 60 60 50 50 40 40 30 pressure [bar] pressure 30 pressure [bar] pressure 20 20 10 10 0 0 -20-100 10203040 -20-100crank angle 10203040 [deg] crank angle [deg]

Figure 5. In-cylinder pressure at 3300 rpm, 80% load. Figure 5. In‐cylinder pressure at 3300 rpm, 80% load. Figure 5. In‐cylinder pressure at 3300 rpm, 80% load. It has to be considered how injection works: ECU establishes the duration of pre-injection 3.2. Jetprocess, A blended thus with to deliver Diesel 1 + mm and3 Biodieselof fuel in from order WCO to analyze the curves. When blends of diesel + and 3.2. Jet A blended with Diesel + and Biodiesel from WCO Jet A are used, the lower values of density and viscosity of aviation fuel alter the properties of the Experimentation was carried out with the aim of using Jet A as additive to enhance the blends.Experimentation The unchanged was carried energizing out timings with injectionthe aim timingsof using cause Jet aA longer as additive duration to of enhance injection, the performance of blends of biodiesel and diesel +, since mixing Jet A with diesel + demonstrated performanceaccording of to blends [36]. These of biodiesel variations and are responsiblediesel +, since for a modificationmixing Jet A of with the mass diesel that + is demonstrated delivered allowing a reduction of NOx. allowingduring a reduction pre-injection; of duringNOx. the main injection, the amount of delivered fuel is established by ECU to At first, it was decided to mix a fixed percentage of Jet A in two blends, which differentiate for guaranteeAt first, it thewas required decided torque to mix value. a fixed The percentage fuel properties of Jet also A a ffinect two spray blends, penetration, which velocity,differentiate and for the biodiesel/diesel + percentage. 10% by volume of Jet A was chosen, since it allows obtaining a the biodiesel/dieselangle [36]. + percentage. 10% by volume of Jet A was chosen, since it allows obtaining a larger reductionWhen DK10 of NO is used,x and Jet a Amoderate in pre-injected increase fuel of delays particulate the first peakmatter of heatas regards release curve.20%. The A larger range of larger reduction of NOx and a moderate increase of particulate matter as regards 20%. The range of biodieselamount blending of heat ratio is released was fixed before by TDC considering as regards that diesel 40%+. is The the high maximum temperature value allows that can for a be fast ready biodiesel blending ratio was fixed by considering that 40% is the maximum value that can be ready to useevaporation in the actual of diesel engine+ in thewithout blend, requiring thus promoting any hardware the oxidation modification; reactions. The values lower cetane of less number than 20% to use in the actual engine without requiring any hardware modification; values of less than 20% havecharacterizing demonstrated Jet to A have causes very an extension low impact of the on heat the releasefuel behaviour curve that [12]. is moved Subsequently, towards the a expansionfixed amount have demonstrated to have very low impact on the fuel behaviour [12]. Subsequently, a fixed amount of biodieselstroke. When was mixed DK20 iswith used, blends the heat of releaseJet A and released diesel before + (two TDC percentages is increased of as Jet regards A were diesel considered).+, the of biodiesel was mixed with blends of Jet A and diesel + (two percentages of Jet A were considered). eFiguresffect of cetane 6–8 present number the on emission moving the characteristics combustion towards of the following the expansion fuels stroke (percentages is more evident by volume): as regardsFigures the 6–8 DK10 present blend. the Mixingemission Jet characteristics A in the blend makes of the the following subsequent fuels combustion (percentages phases by volume): more ‐ DB20K10:contiguous, 70% as diesel in-cylinder +, 20% pressure biodiesel curves from show. waste cooking oil, 10% Jet A ‐ DB20K10: 70% diesel +, 20% biodiesel from waste cooking oil, 10% Jet A ‐ DB40K10: 50% diesel +, 40% biodiesel from waste cooking oil, 10 % Jet A ‐ DB40K10: 50% diesel +, 40% biodiesel from waste cooking oil, 10 % Jet A ‐ DB20: 80% diesel +, 20% biodiesel from waste cooking oil ‐ DB20: 80% diesel +, 20% biodiesel from waste cooking oil

Energies 2019, 12, 2488 9 of 14

3.2. Jet A blended with Diesel + and Biodiesel from WCO Experimentation was carried out with the aim of using Jet A as additive to enhance the performance of blends of biodiesel and diesel +, since mixing Jet A with diesel + demonstrated allowing a reduction of NOx. At first, it was decided to mix a fixed percentage of Jet A in two blends, which differentiate for the biodiesel/diesel + percentage. 10% by volume of Jet A was chosen, since it allows obtaining a larger reduction of NOx and a moderate increase of particulate matter as regards 20%. The range of biodiesel blending ratio was fixed by considering that 40% is the maximum value that can be ready to use in the actual engine without requiring any hardware modification; values of less than 20% have demonstrated to have very low impact on the fuel behaviour [12]. Subsequently, a fixed amount of biodiesel was mixed with blends of Jet A and diesel + (two percentages of Jet A were considered). Figures6–8 present the emission characteristics of the following fuels (percentages by volume):

- DB20K10: 70% diesel +, 20% biodiesel from waste cooking oil, 10% Jet A -Energies DB40K10: 2019, 12, x FOR 50% PEER diesel REVIEW+, 40% biodiesel from waste cooking oil, 10 % Jet A 9 of 13 - DB20: 80% diesel +, 20% biodiesel from waste cooking oil ‐ DB40: 60% diesel + , 40% biodiesel from waste cooking oil - DB40: 60% diesel +, 40% biodiesel from waste cooking oil Under the same amount of biodiesel, substituting a fraction of diesel + with Jet A causes an increaseUnder of CO the samein the amount exhaust of (Figure biodiesel, 6); substituting HC emissions a fraction remain of almost diesel +unchanged.with Jet A causes Under an the increase same amountof CO in of the Jet exhaust A in the (Figure fuels, the6); HCincrease emissions of biodiesel remain content almost is unchanged. responsible Under for a reduction the same of amount the in‐ cylinderof Jet A in temperature the fuels, the according increase with of biodiesel [12], to contentascribe isto responsible the lower heating for a reduction value of ofbiodiesel, the in-cylinder which reducestemperature the accordingamount of with energy [12], tothat ascribe is released. to the lower The heatinglower temperature value of biodiesel, causes which the increase reduces theof hydrocarbonsamount of energy and thatcarbon is released. monoxide The emissions, lower temperature despite the causes biodiesel the higher increase content of hydrocarbons of oxygen that and becomescarbon monoxide less effective. emissions, This behaviour despite the is biodiesel consistent higher with content [16], in ofwhich oxygen the that results becomes that are less related eﬀective. to aThis constant behaviour engine is consistentspeed value with are [ presented.16], in which the results that are related to a constant engine speed value are presented.

0,0450.045 25

0.0400,04 20 0,0350.035

0.0300,03 15 0,0250.025

0.0200,02 CO [%] CO

HC [ppm] 10 0,0150.015

0.0100,01 5 0,0050.005

0 0 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm]

Figure 6. COCO and and HC HC variation variation as as function function of of engine engine speed, speed, 80% load.

InIn Figure 77,, NONOx emissionemission in in terms terms of of NO NO equivalent equivalent is is plotted as a function of engine speed. At a lower engine speed,speed, blendingblending with with Jet Jet A A allows allows for for a a reduction reduction of of the the emission. emission. The The reason reason is isthought thought to to be be related related to to the the faster faster vapour vapour mixing mixing and and the the burning burning properties properties of Jet of A,Jet whichA, which reduces reduces the thetime time that that is available is available for nitrogenfor nitrogen oxides oxides production production [25]. [25]. At higher At higher engine engine speed, speed, when when Jet A Jet is usedA is usedwith biodieselwith biodiesel and diesel and diesel+, its +, longer its longer ignition ignition delay delay is responsible is responsible for afor larger a larger amount amount of fuel of fuel in the in thechamber. chamber. Higher Higher combustion combustion temperatures temperatures are reached, are reached, thus causing thus causing NOx emission NOx emission increase, increase, which is whichin agreement is in agreement with experimental with experimental data related todata the related cetane numberto the cetane eﬀect on number engine effect performance on engine and performanceemissions [34 and]. emissions [34]. Concerning particulate matter emissions, they are generally reduced by adding biodiesel, which is caused by the oxygen presence1000 in biodiesel molecules. Figure8 shows the e ﬀect of biodiesel and Jet A on the particle number and900 mean diameter. When Jet A is mixed in the blend, it is responsible 800

700

600

NO [ppm] 500

400

300

200 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm]

Figure 7. NO variation as function of engine speed, 80% load.

Concerning particulate matter emissions, they are generally reduced by adding biodiesel, which is caused by the oxygen presence in biodiesel molecules. Figure 8 shows the effect of biodiesel and Jet A on the particle number and mean diameter. When Jet A is mixed in the blend, it is responsible for a different behaviour as a function of the engine speed. At lower engine velocity, an increase of particulate matter concentration is observed for both blends with Jet A. Substituting diesel + with Jet A at higher values of engine speed causes a reduction of soot emission, probably to ascribe to the

Energies 2019, 12, x FOR PEER REVIEW 9 of 13

‐ DB40: 60% diesel + , 40% biodiesel from waste cooking oil Under the same amount of biodiesel, substituting a fraction of diesel + with Jet A causes an increase of CO in the exhaust (Figure 6); HC emissions remain almost unchanged. Under the same amount of Jet A in the fuels, the increase of biodiesel content is responsible for a reduction of the in‐ cylinder temperature according with [12], to ascribe to the lower heating value of biodiesel, which reduces the amount of energy that is released. The lower temperature causes the increase of hydrocarbons and carbon monoxide emissions, despite the biodiesel higher content of oxygen that becomes less effective. This behaviour is consistent with [16], in which the results that are related to a constant engine speed value are presented.

0,0450.045 25

0.0400,04 20 0,0350.035

0.0300,03 15 0,0250.025

0.0200,02 CO [%] CO

HC [ppm] 10 0,0150.015

0.0100,01 5 0,0050.005

0 0 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm]

Figure 6. CO and HC variation as function of engine speed, 80% load. Energies 2019, 12, 2488 10 of 14 In Figure 7, NOx emission in terms of NO equivalent is plotted as a function of engine speed. At a lower engine speed, blending with Jet A allows for a reduction of the emission. The reason foris thought a diﬀerent to be behaviour related to asthe a faster function vapour of the mixing engine and speed. the burning At lower properties engine velocity,of Jet A, which an increase reduces of particulatethe time that matter is available concentration for nitrogen is observed oxides for production both blends [25]. with At Jet higher A. Substituting engine speed, diesel when+ with Jet Jet A Ais atused higher with values biodiesel of engine and diesel speed +, causes its longer a reduction ignition ofdelay soot is emission, responsible probably for a larger to ascribe amount to the of higherfuel in fuelthe chamber. volatility Higher of Jet A combustion and the longer temperatures ignition delay are thatreached, lead tothus better causing fuel–air NO mixing.x emission The increase, mixing enhancementwhich is in agreement entails that fewerwith fuel-richexperimental pockets data exist related in the chamberto the cetane thus causing number a reduced effect on formation engine ofperformance soot. and emissions [34].

1000

900

800

700

600

Energies 2019, 12, x FOR PEER REVIEWNO [ppm] 500 10 of 13

400 higher fuel volatility of Jet A and the longer ignition delay that lead to better fuel–air mixing. The 300 mixing enhancement entails that fewer fuel‐rich pockets exist in the chamber thus causing a reduced 200 formation of soot. 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] The mean diameter of emitted particle is characterized by values of around 80 nm for all blends. Higher diameters characterize the emission of DB40K10 (diesel + 50%, biodiesel 40%, and Jet 10% by volume) in almost all Figurethe values 7. NO of variation tested engine as function speed. of engine speed, 80% load. Figure 7. NO variation as function of engine speed, 80% load.

3,5E+083.5X108 1,2E+021.2X102 Concerning particulate matter emissions, they are generally reduced by adding biodiesel, which 3,0E+083.0X108 is caused by the oxygen presence in biodiesel molecules.1,0E+021.0X10 Figure2 8 shows the effect of biodiesel and 2,5E+082.5X108 ]

Jet A3 on the particle number and mean diameter. When Jet A is mixed in the blend, it is responsible 8.0X101 2.0 108 8,0E+01 for a different2,0E+08X behaviour as a function of the engine speed. At lower engine velocity, an increase of 8 1,5E+081.5X10 1 particulate matter concentration is observed for both blendsCMD [nm] 6,0E+016.0X10 with Jet A. Substituting diesel + with Jet Ntot [N/cm Ntot A at higher1,0E+081.0X108 values of engine speed causes a reduction of soot emission, probably to ascribe to the 4,0E+014.0X101 7 5,0E+075.0X10 0,0E+000.0X100 2,0E+012.0X101 2200 2400 2600 2800 3000 3200 3400 3600 3800 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] engine speed [rpm]

FigureFigure 8. 8. ParticleParticle numbernumber concentration concentration and and mean mean diameter diameter variation variation with with engine engine speed, speed, 80% 80% load. load.

TheAimed mean at diameterdeeper investigation of emitted particle the impact is characterized of Jet A in the by blend, values some of around tests have 80 nm been for performed all blends. Higherwith a variation diameters of characterize aviation fuel the percentage emission ofin DB40K10a mixture (dieselcontaining+ 50%, 30% biodiesel by volume 40%, of andbiodiesel. Jet 10% Such by volume)a value was in almost selected all thebased values on the of testedpreviously engine presented speed. results, which have demonstrated how this percentageAimed atbehaves deeper as investigation a compromise the between impact of 20 Jet and A in40%. the Investigations blend, some tests were have devoted been performedto evaluate withthe effect a variation of Jet of A aviation percentage fuel percentagein a blend inin awhich mixture the containing amount of 30% biodiesel by volume was of fixed biodiesel. (Jet A Such was aincreased value was in selected detriment based of diesel on the + quantity). previously Three presented blends results, were tested which (percentages have demonstrated by volume): how this percentage behaves as a compromise between 20 and 40%. Investigations were devoted to evaluate the e‐ ﬀDB30:ect of Jet70% A diesel percentage +, 30% in biodiesel a blend in from which waste the amountcooking ofoil biodiesel was ﬁxed (Jet A was increased in detriment‐ DB30K10: of 60% diesel diesel+ quantity). +, biodiesel Three from blends WCO were 30%, tested Jet A (percentages10% by volume by volume): ‐ DB30K20: diesel + 50%, biodiesel from WCO 30%, Jet A 20% by volume - DB30: 70% diesel +, 30% biodiesel from waste cooking oil Figure 9 shows the CO and HC concentration in the exhaust. Adding Jet A causes a small - DB30K10: 60% diesel +, biodiesel from WCO 30%, Jet A 10% by volume increase of both emissions. - DB30K20: diesel + 50%, biodiesel from WCO 30%, Jet A 20% by volume

0,0450.045 25

Figure0.0400,04 9 shows the CO and HC concentration in the exhaust. Adding Jet A causes a small increase of both0,0350.035 emissions. 20

0.0300,03 15 0,0250.025

0.0200,02 CO [%] 10 HC [ppm] 0,0150.015

0.0100,01 5 0,0050.005

0 0 2200 2400 2600 2800 3000 3200 3400 3600 3800 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] engine speed [rpm]

Figure 9. CO and HC variation as function of engine speed, 80% load.

Figure 10 shows that the effect of Jet A on NOx emission is almost negligible.

Energies 2019, 12, x FOR PEER REVIEW 10 of 13 higher fuel volatility of Jet A and the longer ignition delay that lead to better fuel–air mixing. The mixing enhancement entails that fewer fuel‐rich pockets exist in the chamber thus causing a reduced formation of soot. The mean diameter of emitted particle is characterized by values of around 80 nm for all blends. EnergiesHigher2019 diameters, 12, 2488 characterize the emission of DB40K10 (diesel + 50%, biodiesel 40%, and Jet 10%11 of 14by volume) in almost all the values of tested engine speed.

3,5E+083.5X108 1,2E+021.2X102

3,0E+083.0X108 1,0E+021.0X102 2,5E+082.5X108 ] 3 8,0E+018.0X101 2,0E+082.0X108

8 1,5E+081.5X10 1

CMD [nm] 6,0E+016.0X10 Ntot [N/cm Ntot 1,0E+081.0X108 4,0E+014.0X101 5,0E+075.0X107

0,0E+000.0X100 2,0E+012.0X101 2200 2400 2600 2800 3000 3200 3400 3600 3800 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] engine speed [rpm]

Energies 2019, 12, x FOR PEER REVIEW 11 of 13 Figure 8. ParticleFigure number 9. CO concentration and HC variation and mean as function diameter of engine variation speed, with 80% engine load. speed, 80% load. 1000

900 EnergiesFigureAimed 2019, 1012 at, showsx deeper FOR PEER that investigation REVIEW the eﬀect of the Jet impact A on NO of Jetx emission A in the is blend, almost some negligible. tests have been performed11 of 13 with a variation of aviation fuel800 percentage in a mixture containing 30% by volume of biodiesel. Such 1000 a value was selected based on700 the previously presented results, which have demonstrated how this 900 percentage behaves as a compromise600 between 20 and 40%. Investigations were devoted to evaluate 800 the effect of Jet A percentageNO [ppm] 500 in a blend in which the amount of biodiesel was fixed (Jet A was 700 increased in detriment of diesel400 + quantity). Three blends were tested (percentages by volume): 600 300

‐ DB30: 70% diesel +, 30% biodieselNO [ppm] 500 from waste cooking oil 200 ‐ DB30K10: 60% diesel +, biodiesel2200 from 2400 WCO 2600 2800 30%, 3000 Jet 3200 A 10% 3400 by 3600 volume 3800 400 engine speed [rpm] ‐ DB30K20: diesel + 50%, biodiesel300 from WCO 30%, Jet A 20% by volume

200 Figure 9 shows the CO and2200 HC 2400 concentration 2600 2800 3000 in 3200 the 3400 exhaust. 3600 3800 Adding Jet A causes a small engine speed [rpm] increase of both emissions.Figure 10. NO variation with engine speed at 80% load.

0,045 Concerning0.045 particulate emission (Figure 11), a reduction25 was obtained in the complete engine 0.0400,04 speed range while addingFigureFigure Jet 10. A10. NO inNO the variation variation fuel. with Thewith engine decreaseengine speed speed in at atsoot 80% 80% is load. load. particularly significant for 0,0350.035 20

DB30K10.0.0300,03 ConcerningConcerning particulateparticulate emissionemission (Figure(Figure 1111),), aa reduction reduction15 was was obtained obtained in in the the complete complete engine engine Particle0,0250.025 diameters have a moderate decrease with the engine speed, but there are almost no speedspeed0.020 range0,02 range while while adding adding Jet AJet in A the in fuel. the Thefuel. decrease The decrease in soot isin particularlysoot is particularly signiﬁcant significant for DB30K10. for differenceCO [%] among the fuels. 10 HC [ppm] DB30K10.0,0150.015 3,5E+083.5X108 1,2E+021.2 102 0.0100,01 X Particle diameters have a moderate decrease with 5the engine speed, but there are almost no difference3,0E+083.00,0050.005X108 among the fuels. 1,0E+021.0X102 2,5E+082.5X1008 0 2200 2400 2600 2800 3000 3200 3400 3600 3800 3,5E+088 22002 2400 2600 2800 3000 3200 3400 3600 3800 ] 3.5X10 1,2E+021.2X10 3 engine speed [rpm] 8.0X101 engine speed [rpm] 2,0E+082.0X108 8,0E+01 3,0E+083.0X108 2 8 1,0E+021.0X10 1,5E+081.5X10 1

CMD [nm] CMD 6,0E+016.0X10 Ntot[N/cm 2,5E+082.5X108 8

1,0E+08] 1.0X10 Figure 9. CO and HC variation as function of engine speed, 80% load. 3 8.0X101 2,0E+082.0X108 8,0E+01 4,0E+014.0X101 5,0E+075.0X107 1,5E+081.5 108 X x 1 Figure 10 shows that the effect of Jet A on NO emission[nm] CMD 6,0E+016.0X10 is almost negligible. 0,0E+00Ntot[N/cm 0.0 X100 2,0E+012.0X101 1,0E+081.0X1022008 2400 2600 2800 3000 3200 3400 3600 3800 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] engine speed [rpm] 4,0E+014.0X101 5,0E+075.0X107

0,0E+000.0X100 2,0E+012.0X101 2200 2400 2600 2800 3000 3200 3400 3600 3800 2200 2400 2600 2800 3000 3200 3400 3600 3800 engine speed [rpm] engine speed [rpm] Figure 11. Particle number concentration and mean diameter variation as function of engine speed, 80% load.

4. ConclusionsParticleFigure 11. diameters Particle number have a concentration moderate decrease and mean with diameter the engine variation speed, as function but there of engine are almostspeed, no diﬀerence80% load. among the fuels. An experimental analysis was carried out to evaluate the potential use in diesel engines of Jet A, along with blends of petrol diesel, renewable diesel, and biodiesel. 4. Conclusions Previous research activity highlighted that biodiesel use in blend with renewable diesel and petrolAn diesel experimental enhances carbonanalysis monoxide, was carried hydrocarbons, out to evaluate and the particulate potential usematter in diesel emissions engines as regardsof Jet A, petrolalong dieselwith blends with an of increasepetrol diesel, of nitrogen renewable oxides diesel, emission. and biodiesel. Moreover, a maximum value of biodiesel amountPrevious in the blendresearch was activity defined, highlighted in order to thatguarantee biodiesel a correct use in engine blend operationwith renewable without diesel the need and ofpetrol hardware diesel modification. enhances carbon monoxide, hydrocarbons, and particulate matter emissions as regards petrolTesting diesel was with performed an increase to of analyze nitrogen whether oxides mixing emission. Jet Moreover,A in a blend a maximumcontaining value biodiesel of biodiesel allows foramount mitigating in the the blend drawbacks was defined, of biodiesel in order and to obtainingguarantee an a correct improvement engine operationof the exhaust without emission. the need of hardware Blends containingmodification. different percentages of Jet A and biodiesel from WCO were investigated as a functionTesting of thewas engine performed speed, to keepinganalyze thewhether load conditionmixing Jet constant. A in a blend The containingresults indicate biodiesel that, allowswhen 10%for mitigating of Jet A is theadded drawbacks to blends of containingbiodiesel and diesel obtaining + and biodieselan improvement from WCO of the (DB20K10, exhaust emission. DB40K10), the relation Blends between containing emissions different and percentages engine speed of Jet remains A and biodieselalmost unchanged from WCO as were regards investigated the trends as thata function were observed of the engine with blendsspeed, ofkeeping diesel +the and load WCO condition biodiesel. constant. CO and The HC results have a indicate weak dependence that, when on10% the of engine Jet A speedis added values; to blends NO is containingcharacterized diesel by a+ reduction and biodiesel with froman engine WCO speed (DB20K10, increase. DB40K10), Particle numberthe relation density between in the emissions exhaust shows and engine an increment speed remains with the almost engine unchanged speed increase. as regards At lower the values trends that were observed with blends of diesel + and WCO biodiesel. CO and HC have a weak dependence on the engine speed values; NO is characterized by a reduction with an engine speed increase. Particle number density in the exhaust shows an increment with the engine speed increase. At lower values

Energies 2019, 12, 2488 12 of 14

4. Conclusions An experimental analysis was carried out to evaluate the potential use in diesel engines of Jet A, along with blends of petrol diesel, renewable diesel, and biodiesel. Previous research activity highlighted that biodiesel use in blend with renewable diesel and petrol diesel enhances carbon monoxide, hydrocarbons, and particulate matter emissions as regards petrol diesel with an increase of nitrogen oxides emission. Moreover, a maximum value of biodiesel amount in the blend was defined, in order to guarantee a correct engine operation without the need of hardware modification. Testing was performed to analyze whether mixing Jet A in a blend containing biodiesel allows for mitigating the drawbacks of biodiesel and obtaining an improvement of the exhaust emission. Blends containing different percentages of Jet A and biodiesel from WCO were investigated as a function of the engine speed, keeping the load condition constant. The results indicate that, when 10% of Jet A is added to blends containing diesel + and biodiesel from WCO (DB20K10, DB40K10), the relation between emissions and engine speed remains almost unchanged as regards the trends that were observed with blends of diesel + and WCO biodiesel. CO and HC have a weak dependence on the engine speed values; NO is characterized by a reduction with an engine speed increase. Particle number density in the exhaust shows an increment with the engine speed increase. At lower values of engine speed NO is reduced, but particle number concentration increases; at higher values of engine speed, these emissions behave in the opposite way. The experimental data indicate that mixing diesel + with 30% by volume of biodiesel and 10% or 20% of Jet A allows for an enhancement of NOx emission. In the exhaust flow, the concentration of soot was reduced, especially at lower values of engine speed; the number of particles decreased and the mean diameters of particle remain almost unchanged. The test results suggest that using Jet A could be a way to increase the amount of renewable fuel in diesel engines, without penalizing the pollutant emission.

Author Contributions: Conceptualization: G.C. and O.C.; Investigation: F.P.; Formal analysis: O.C.; Resources: O.C.; Supervision: G.C.; Visualization: O.C.; Writing—original draft O.C.; Writing—review & editing: O.C. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂicts of interest.

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