Backfire Prediction in a Manifold Injection Hydrogen Internal Combustion Engine

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INTERNATIONALJOURNALOFHYDROGENENERGY33 (2008) 3847– 3855

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Backﬁre prediction in a manifold injection hydrogen internal combustion engine

Xing-hua Liua, Fu-shui Liua, Lei Zhoua,Ã, Bai-gang Suna, Harold. J. Schockb aSchool of Mechanical and Vehicular Engineering, Beijing Institute of Technology, Beijing 100081, China bEngine Research Laboratory, Michigan State University, East Lansing, MI, USA article info abstract

Article history: Hydrogen internal combustion engine (H2ICE) easily occur inlet manifold backfire and Received 27 July 2007 other abnormal combustion phenomena because of the low ignition energy, wide Received in revised form flammability range and rapid combustion speed of hydrogen. In this paper, the effect of 26 April 2008 injection timing on mixture formation in a manifold injection H2ICE was studied in various Accepted 28 April 2008 engine speed and equivalence ratio by CFD simulation. It was concluded that H2ICE of Available online 16 June 2008 manifold injection have an limited injection end timing in order to prevent backfire in the inlet manifold. Finally, the limit of injection end timing of the H2ICE was proposed and Keywords: validated by engine experiment. Hydrogen internal combustion & 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights engine (H2ICE) reserved. Backfire Injection timing CFD Simulation

1. Introduction 1.2. Literature review

1.1. Background 1.2.1. Experiment study on backfire in H2ICE In the experiments of the hydrogen engine, the problem of As a new type of internal combustion engine, the difference backfire and rapid rate of pressure rise were frequently between H2ICE and gasoline was chiefly induced by the experienced. A close study on hydrogen–oxygen combustion difference of physical features between these two types of mechanism is very important, primarily with an objective to fuels. Compared with gasoline, the advantages of hydrogen, assess how different it is from petroleum-based liquid fuels such as high flammability, low ignition energy, good homo- as to combustion. genous combustion, high octane number and high thermo- From the literature, the single greatest issue regarding dynamic efficiency, had been analyzed in most papers [1–3]. spark-ignited H2ICE combustion is backfire and/or pre-igni- However, because the ignition energy of hydrogen–air tion occurring as a lean fuel/air ratio approaches stoichio- mixtures is very small, the first obstacle regarding spark- metric, which limits the torque output of the engine [4]. ignited (SI) H2ICE combustion are backfire, pre-ignition and Backfire is the condition when the fresh charge of hydrogen is knocking; especially for a manifold injection H2ICE, the back ignited in intake ports. Pre-ignition is the condition when the fire is the first obstacle which should be overcome by a hydrogen charge is ignited after the intake valve closes and designer. before the spark plug fires in cylinder.

ÃCorresponding author. Tel.: +86 10 68912516. E-mail address: [email protected] (L. Zhou). 0360-3199/$ - see front matter & 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2008.04.051 ARTICLE IN PRESS

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Nomenclature EVO exhaust valve open Phi equivalence ratio IVC intake valve close TDC top dead center (3601 CA in this paper) IVO intake valve open BDC bottom dead center EVC exhaust valve close

The intake process is complicated considering the gas and in-cylinder with respect to different engine speeds and dynamics of the intake and exhaust, and so it is possible that equivalence ratios. We can obtain an optimal injection timing a rich pocket of hydrogen could also exist that would locally for avoiding backfire based on the analysis of CFD simulation. be the first to ignite especially in a manifold injection hydrogen engine. 1.2.2. Simulation study on backfire in H2ICE It has been suggested in the literature [5] that backfire can Johnson [8] uses the Kiva-3 V engine simulation code devel- be controlled by injecting the hydrogen only during the oped at Los Alamos National Laboratory with the standard forward flow of air into the cylinder during the intake stroke, eddy-turnover model to simulate a hydrogen engine at a fixed thus minimizing the fuel’s exposure to being heated or equivalence ratio and volumetric efficiency. The standard coming into contact with hot spots or hot oil ash/residual in model contains one free parameter that is adapted for the combustion chamber. hydrogen and held constant for varying ignition timing and Isadore and Frank [6] haddetailedanalysisoftheflamm- engine speed. The model is validated against the experiments ability limits of hydrogen–air mixture. They concluded that the reported in Ref. [9]. Fontana et al. [10] modified the Kiva-3 V lean limit occurs at lower concentration as the mixture code to simulate an SI engine fuelled with a hydrogen/ temperature increase with a linear relationship, while the gasoline mixture. They used a hybrid model where the global pressure effect appears to be small. They gave the lean limit up reaction rate is either given by the standard eddy-turnover to 400 1C (673.15 K) mixture temperature. Since this tempera- model or a weighed reaction rate based on two global reaction ture range is not enough to cover the ignition temperature in rate expressions, one for hydrogen combustion and one for engine condition, the lean limit line is extended up to 700 1C gasoline. They validated the model for gasoline operation and (973.15 K) and plotted in Fig. 1. Thus, concentration is the most calculated the effects of adding various hydrogen concentra- sensitive parameter for controlling hydrogen self-ignition and, tions to gasoline. GM company optimized the mixture of course, backfire. formation of the H2ICE [11] using CFD-simulation method It is necessary for developers to put up a close study for the and found the conclusion that injection timing should be hydrogen mixture formation both in the inlet and in-cylinder advanced with engine speed increasing, and the injection to avoid the backfire with respect to injection timing. Keck [7] duration should be completed before intake valves closed. reports measurements in an optically accessible engine, However, the objective of their study are the improvement of operated on propane as well as hydrogen, and uses a the output of the H2ICE. turbulent entrainment model to compare predicted trends In order to optimize the intake charge and mixture with experimentally observed trends. In fact, by means of the formation in H2ICE, a CFD simulation of injector locations 3D-CFD-simulation (full analysis of the fluid motion), it is and timing in different engine operation was conducted nowadays possible to gain a deep insight of the processes that by BWM [12], and two important conclusions were proposed: govern engine performance and emissions, and the 3D-CFD- (1) in order to avoid backfire, it is greatly important to select simulation represents the most sophisticated approach injector location and injection timing; (2) if the injection for the detailed numerical investigation on any fluid-dyna- timing is too early, it will let mixture flow back to manifold mical problem. Consequently, the CFD simulation is the best while intake valves nearly closing. As a result, delay the tools to demonstrate the mixture formation both of intake injection timing as much as possible, it can make part of air enter the cylinder to cool the hot pots first, and lower the possibility of backfire. Their studies may be more valuable if they had gave a recommendation or a range of hydrogen injection timing, and which is the focus of this paper.

1.3. Motivation and objective

Frankly, the most recent efforts into H2ICE simulation focus on CFD calculation of DI engines which have nothing to do with the backfire. A team from TU Graz and BMW has reported CFD simulations of the mixing process in DI engines [13] and is now working on the CFD simulation of the combustion process [14]. Nevertheless, the DI H2ICE has a very complex structure of cylinder head and a huge cost for Fig. 1 – Influence of temperature on hydrogen lean production; so it is impractical to develop DI H2ICEs for flammability limit. automobiles in the near future. Actually, the hydrogen ARTICLE IN PRESS

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powered cars produced by BMW and FORD were equipped with manifold injection H2ICE rather than DI H2ICE. Thus, it 2. Materials and methods is very important to discover the methods of avoiding the backfire in the manifolds for this type of H2ICE. 2.1. Approach Although we can get an in-cylinder image of mixture formation by experiment of optical-H2ICE, little information After an exhaustive study to identify the various causes of of intake ducts and ports can be obtained. In addition, it is backfire, it was clearly observed that the injection configura- difficult to make experiments of optical-H2ICE on high speed tion of the gasoline engine is not appropriate for a fuel such and load which is the operation of frequently backfire. as hydrogen which has combustion characteristics widely Furthermore, the bench experiments indicate that correct different from conventional petroleum fuels. The reason and injection timing is one of the key factors to avoid backfire. possible solve methods for backfire in manifold injection Consequently, it is necessary to explore an injection timing H2ICE is demonstrated in Table 1. range to avoid the backfire in H2ICE by CFD simulation, and As shown in Table 1, minimizing the hydrogen residual in we will discuss it in the following text. the manifold after the intake valve closure is the way to lower the backfire possibility. Based on Table 3, the backfire possibility will increase either hydrogen injection start too early or end too later when the valve timing is fixed. Fig. 2 Table 1 – The ignition source and possible solve methods gives a relationship between the injection configuration and for backfire in a manifold injection H2ICE backfire possibility. In Fig. 2 the total mass of injected hydrogen per cycle is represented by the area of the The source of Ignition Possible solve trapezium which is depend on the engine speed and load. residual in the source methods In fact, when the injection pressure which is represented by intake ports the height of the trapezium in Fig. 7 is fixed, the injection

Former cycle High Setup an appropriately duration is determined by the engine speed and load. In temperature injection timing shorten summary, each engine operation case has its corresponding exhaust gas the overlap injection duration. Consequently, there should be an appropriately injection timing to avoid backﬁre for each engine Former cycle High Setup an appropriately temperature injection timing operation case. spots Advance the IVC 2.2. Calibration of hydrogen injector Current cycle High Postpone the IVO temperature For the hydrogen engine modiﬁed from a gasoline engine, the exhaust gas Postpone the hydrogen injectors should be altered for the gaseous fuel hydrogen. injection CNG injectors of Landirenzo have been adapted to the hydrogen engine (Fig. 3, Table 2). In order to investigate Current cycle High Postpone the hydrogen the characteristic for hydrogen injection of the injectors, temperature injection spots an experiment system special for the research of the injector

Fig. 2 – The hydrogen injection and possibility of backﬁre. ARTICLE IN PRESS

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has been designed and used to get the hydrogen injection characteristic. Fig. 4 gives the result of the hydrogen injection characteristic of this injector with the injection pressure 2 bar.

2.3. H2ICE experiment

In the initial attempts of introducing hydrogen to an engine, hydrogen fuel system and corresponding injectors were adopted for a 4-cylinders SI engine (Table 3). This study was aimed at developing an existing engine system to accept hydrogen as a alternative fuel for the conventional gasoline. Moreover, the hydrogen engine could be operated with good performance in its own characteristics based on a detailed theoretical and experimental investigation of altering the injection timing, spark timing and many other important parameters when the engine was running (Fig. 5). The engine experiment was carried out at different engine speed (from 2000 to 5000 r/min at the interval 1000 r/min) with wide open throttle but different concentrations. The ignition timing was ﬁxed at 345 1CA. The conﬁguration of injector installation was shown in Fig. 6. Fig. 7 shows the schematic of the H2ICE experimental system. Thereare5partsintheBIT-H2ICElab,theyaredescribedas below:

Test bench measurement and control system: Dynamometer Fig. 3 – Hydrogen injector experiment system. and engine test measurement system and AVL exhaust gas analyzer. The combustion analyzer: Dewetron analyzer and Kistler spark plug cylinder pressure sensors and instantaneous Table 2 – Landirenzo injector specifications intake manifold pressure sensors are installed. Fuel delivery system: Hydrogen is supplied from sixteen \ Type of fuel LPG/CNG bottles ð40 L 150 barÞ. The hydrogen flow through an emergency shut down valve, two stages pressure Opening voltage 6/16 V regulators and measured by a Coriolis flow meter. Maximum frequency 200 Hz Lab safety system: the dynamometer cell is equipped with Opening time 1.5 ms two hydrogen concentration sensors. In case of hydrogen Closing time 1.5 ms Injector hole diameter 4 mm leaking, alarm light and siren act, then ventilation system start to work automatically. Engine electrical control system: A self-made ECU is used for the hydrogen engine control by using MATLAB/SIMULINK, and convert it to dSPACE system which manages engine operation.

During the experiment, at each engine speed operation, with the increase of injection duration, the experiment should be stopped under exceptional noise with abnormal combustion (pre-ignition, backﬁre or knocking).

2.4. Setup of simulation model

In order to guarantee that the simulation model has a good reliability for air and hydrogen flow simulation, a comparison of air mass flow between experiment and simulation is shown in Table 4. In Table 4, the simulation of air mass flow nearly has a Fig. 4 – Hydrogen injection mass at 2 bar. same result with the experiment. However, the simulation ARTICLE IN PRESS

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Fig. 5 – Hydrogen engine research and development platform.

Table 3 – Basic parameters of the H2ICE Based on the analysis above, the simulation model has been validated for the further calculation. Moreover, the setup of Type Four cylinders in boundary at air inlet and hydrogen injector inlet was shown line, water cooling in Table 5. Valve configuration DOHC 4 V Bore (mm) 86 Stroke (mm) 86 3. Results and discussion Connecting rod length (mm) 142.8 Compression ratio 10.5 3.1. Simulation results Displacement (ml) 1998 Rated power (kW) 60 (5500 r/min) Maximum torque (Nm) 111 (4000 r/min) The hydrogen injection and mixture formation was calcu- Diameter of intake valve head (mm) 37.6 lated with the mesh shown in Fig. 8. Fig. 10 demonstrates the Diameter of exhaust valve head (mm) 27.06 simulation results with injection pressure 2 bar and duration Opening of the intake valve 3381 12 ms at 5000 r/min. At this operation case, the total mass of 1 Closure of the intake valve 608 the injected hydrogen should be 10 mg per cylinder per cycle, Opening of the exhaust valve 1421 and the equivalence ratio is 0.7. Closure of the exhaust valve 3901 Injector: Landirenzo (two injectors per From Fig. 10, the following phenomenons can be observed: cylinder) (1) Postponing the hydrogen injection end, the concentration of hydrogen mixture residual at the intake port decreased at first and then increased rapidly; result usually greater than the experiment data. These errors (2) When the injection end is later than 5201, there will be more could be analyzed as following: and more hydrogen residual in the intake port after the intake valve closure with the delaying of injection timing; (1) Due to the limitation of computation mesh, the intake (3) When the injection end is earlier than 5001, however, the course is from 3701 to 5751 in the simulation which is concentration of hydrogen residual in the intake port keep smaller than the actual intake course (from 3381 to 6081)as almost the same value. shown in Figs. 8 and 9. As a result, the backflow of exhaust gas could not be accurately took into account in the Fig. 11 shows the 3-D process of three typical cases and gives simulation. But, this error could be minimized due to the the explanation of the above phenomenon: In the 5401 injection lash of intake valve in the real engine. end case, the injection end is so late that the hydrogen cannot (2) Only one cylinder has been taken into account in the mass enter the cylinder completely and causes the hydrogen residual. flow calculation in simulation, but the experiment data But in the early injection cases, the hydrogen residual is caused has been calculated by four cylinders. The unbalance by the back flow from the cylinder before intake valve closure. among four cylinders would lead to some difference Therefore, when the engine speed and the equivalence ratio between simulation and calculation; fixed, there should be a limited hydrogen injection end (3) The blow-by has not been considered in the simulation; so timing. When the injection end angle is later than that the air mass flow is greater than experiment. limited valve, the injected hydrogen cannot flow into the ARTICLE IN PRESS

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Fig. 6 – The conﬁguration of hydrogen injector installation.

Fig. 7 – Schematic of the H2ICE experimental system.

Table 4 – Comparison of air mass ﬂow between experiment and simulation

Speed Equivalence Experiment of air Simulation of air Error (r/ ratio mass ﬂow (kg/h) mass ﬂow (kg/h) (%) min)

1000 0.80 49.76 51.86 4.22 2000 0.82 91.02 93.82 3.08 3000 0.77 141.92 145.82 2.75 4000 0.75 201.55 205.91 2.16 5000 0.62 284.72 290.22 1.93

cylinder completely and caused quantity of the hydrogen residual increase rapidly, which will increase the possibility of back ﬁre in the next cycle. Fig. 8 – Calculation mesh. ARTICLE IN PRESS

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Fig. 9 – The difference between simulation mesh and actual intake course.

Table 5 – Boundary condition setup of the model

Boundary name Boundary Boundary condition setup condition

Air inlet Total pressure Pressure (Pa) 98 100–101 600 (According to engine speed) Temperature (K) 293

Species N2 ð76:8%ÞþO2 (23.2%) Hydrogen injector Mass ﬂow rate Mass ﬂow rate (g/s) According to Fig. 4 at different engine speed Temperature (K) 293

Species H2

Fig. 10 – H2 residual at intake port at 5000 r/min.

Based on the above discussion, the limited hydrogen injection ends, from low to high speed and at different mixture concentration, have been calculated as shown in Fig. 12.From this ﬁgure, the higher the engine speed and the richer the Fig. 11 – Hydrogen distribution of different injection end. hydrogen mixture, the earlier the limited injection end.

3.2. Experiment validation for the simulation The experiment starts from a lean mixture, and increases mixture concentration by increase of the injection duration The normal combustion limit of the H2ICE under this and sweeping the injection timing to get the highest output conﬁguration was conducted by engine experiment. power at each engine speed (Fig. 13). ARTICLE IN PRESS

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Fig. 12 – Hydrogen injection end limit in different engine speed and equivalence ratio.

Fig. 14 – Injection end due to backﬁre by experiment.

Fig. 13 – Maximum equivalence ratio and torque of H2ICE.

Fig. 15 – The mean injection end at different engine speed by For each engine speed and its corresponding maximum experiment. loads of normal combustion, 10 times of sweep of injection timing was processed to ﬁnd the late injection limits. Fig. 14 shows the experimental results. The comparison between the averaged experiment results can give a directive trend and rough limit value for H2ICE and the simulation prediction was shown in Fig. 15. calibration. Fig. 15 shows good agreement between experimental result Actually, besides the injection timing, the reasons for and simulation prediction. Even though there is little limiting the equivalence ratio lied on a lot of factors, such difference, simulation results give a reasonable trend and as injector position, injection direction, injection rate, ignition roughly correct limit value. timing and thermal load, etc., which are out of the range of The difference between experimental result and simulation this paper. prediction could be caused by the following factors: Unfortunately, for this injection conﬁguration, our results are only conducted by a single-cycle simulation of the (1) The difference between simulation model and actual mixture formation in the H2ICE, so the prediction of intake course as shown in Fig. 9, will bring out some the simulation could not be taken into account of the effect errors into the calculation result; of the former cycle and the interaction among different (2) The residual of the exhaust gas in-cylinder in the real cylinders. However, these problems could be solved if we engine was considered in the CFD simulation, which is make a multi-cycle and multi-cylinder simulation and con- based on the assumption of uniform discharge of fresh air sider the variation of the boundary temperature, and which is in-cylinder at initial state; the focus of our next paper. (3) The error of the simulation was also induced by a small difference of injection rate between simulation and experiment due to the lag of the injector open. 4. Conclusion

Experiment validation demonstrates that CFD simulation of The CFD simulation is the effective tools to demonstrate the hydrogen injection timing end limit is a valuable and reliable mixture formation process with respect to different engine way to avoid backﬁre in the H2ICE. At least, CFD prediction speeds and equivalence ratios. Based on the above analysis ARTICLE IN PRESS

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and discussion, the conclusions and recommendations were [4] Tang XG, Daniel MK, Robert JN, et al. Ford P2000 hydrogen provided as following: engine dynamometer development. SAE paper no. 2002-01- 0242; 2002. [5] Swain MR, et al. Design and testing of a dedicated hydrogen- (1) The possibility of backfire mainly depends on the con- fueled engine. SAE paper no. 961077; 1996. centration of H2 residual at intake ports in a manifold [6] Isadore LD, Frank EB. Survey of hydrogen combustion injection H2ICE, and the leaner the concentration of the properties. Supersedes NACA research memorandum residual, the lower the possibility of the backfire; E57D24, Report 1383; 1958. (2) The limit of injection end are located in a fixed range at [7] Keck JC. Turbulent flame structure and speed in spark- each engine operation; ignition engines. Proc Combust Inst 1982;145:1–66. (3) The lower the engine speed and the richer the hydrogen [8] Johnson NL. Hydrogen as a zero-emission, high-efficiency fuel: uniqueness, experiments and simulation. In: 3rd inter- mixture, the earlier the injection end. national conference on ICE97 internal combustion engines: experiments and modeling, Naples; 1997. [9] Van Blarigan P. Development of a hydrogen-fuelled internal Acknowledgments combustion engine designed for single speed/power operation. SAE paper no. 961690;1996. This study was supported by the National High-Tech Research [10] Fontana G, Galloni E, Jannelli E, Minutillo M. Numerical and Development Program of China (863 Program) for new modeling of a spark ignition engine using premixed lean energy vehicle (2006AA11A1B6). The authors would like to gasoline–hydrogen–air mixtures. In: 14th world hydrogen express their gratitude for support received from Automobile energy conference, Montreal; 2002. [11] Sierens R, Verhelst S. Influence of the injection parameters Engineering Institute of Chongqing Chang-An Automobile CO. on the efficiency and power output of a hydrogen fueled LTD, Kistler Company, and AVL.List Company, Shanghai. engine. Trans ASME 2003;195(3):444–9. [12] Berckmuller M, Rottengruber H, Eder A, et al. Potentials of a REFERENCES charged SI-hydrogen engine. SAE Paper no. 013210; 2003. [13] Wimmer A, Wallner T, Ringler J, Gerbig F. H2-direct injection—a highly promising combustion concept. SAE paper no. 2005-01-0108; 2005. [1] Negurescu N, Pana C, Ginu M, Soare D. Aspects regarding the [14] Gerke U, Boulouchos K, Wimmer A. Numerical analysis of the combustion of hydrogen in spark ignition engine. SAE paper mixture formation and combustion process in a direct no. 2006-01-0651; 2006. injected hydrogen internal combustion engine. In: 1st inter- [2] Sierens R, Verhelst S. Experimental study of a hydrogen- national symposium on hydrogen internal combustion fueled engine. Trans ASME J Eng Gas Turbines Power engines, Graz; 2006. 2001;123:211–6. [3] Fushui L. CFD study on hydrogen engine mixture formation and combustion. Gottingen: Cuvillier Press; 2004.