ITM Web of Conferences 15, 03002 (2017) DOI: 10.1051/itmconf/20171503002 CMES’17 Charging process analysis of an opposed-piston two-stroke aircraft Diesel engine Łukasz Grabowski1,*, Konrad Pietrykowski1, and Paweł Karpiński1 1Lublin University of Technology, Faculty of Mechanical Engineering, Department of Thermodynamics, Fluid Mechanics and Aviation Propulsion Systems, Nadbystrzycka 36, 20-618 Lublin, Poland Abstract. This paper presents the research results on a 1D model of an opposed-piston two-stroke aircraft Diesel engine. The research aimed at creating a model of the engine in question to investigate how engine performance is affected by the compressor gear ratio. The power was constant at all the operating points. The research results are presented as graphs of power consumed by the compressor, compressor efficiency and brake specific fuel consumption. The optimal range of compressor gear ratio in terms of engine efficiency was defined from the research results. 1 Introduction scavenging is important. This process was investigated using a simulation model and in experiments [4]. The Civil aviation widely uses four-stroke piston spark paper [5] discusses the numerical optimization of basic ignition engines to power light aircrafts such as: planes, operational parameters of the two-stroke aircraft Diesel helicopters, gyroplanes, unmanned aircrafts or UAVs. engine using a patented valve that improves scavenging. This paper shows the model of a supercharged two- Cylinder filling efficiency in two-stroke engines is stroke compression-ignition aircraft engine. This type of inversely proportional to scavenging efficiency. Keeping engine is discussed in few works only so we have balance between these two processes is fundamental for decided to investigate it more broadly in view of the fact engine performance and brake specific fuel that the two-stroke compression-ignition opposed-piston consumption. The optimization method involving Diesel engine shows many advantages, such as a simple improved performance and reduced fuel consumption for design, a good balance, high thermal efficiency, high a forced induced compression-ignition two-stroke specific power and lower wear rate due to friction forces aircraft engine is described in [6]. compared to the four-stroke row engine [1]. The paper [7] presents different methods for force Its drawback is increased fuel consumption and higher inducing the two-stroke aircraft Diesel engine. emission of toxic substances compared to the four-stroke A mechanical compressor increases brake specific fuel engine. It was therefore resolved that the two-stroke Diesel consumption more than a turbocharger. However, this engine carbon dioxide emission ought to be reduced [2]. method of forced induction has a lower mass and A supercharged system is a key component of the dimensions, which is particularly important while model of the entire engine because a correctly defined designing aircraft structures. process boosts the results in a correctly mapped working According to [8], power absorbed by the compressor process. A correctly mapped forced induction is changes with the required amount of air and EGR valve fundamental due to the changes in pressure in the and results from engine mapping. Two different gear combustion chamber and engine performance. Forced ratios between the compressor and the drive shaft for induction can be carried out with a turbocharger or different speeds and load conditions can improve engine a mechanical compressor. The simulation and the performance. experimental research into a turbocharger for car engine The resulting engine power is affected not only by applications using a 1D modelling of the transient and forced induction but also the nature of combustion. The intransient flow is discussed in [3]. The research showed researchers [9] investigated combustion in the opposed- that time lag in the model of a turbocharger enables us to piston two-stroke Diesel engine for heat release rate and more efficiently predict the change in pressure and combustion time. oscillations in mass air flow because of more precisely This work presents a model of an engine and a forced calculated mass and energy stored in the device, which is induction system for the designed 100 kW opposed-piston obtained by a better described propagation of pressure two-stroke Diesel engine aircraft system and gives an waves. account of preliminary simulation. The research aimed at In two-stroke engines, apart from parameters and using the created engine model to investigate the effect of the design of the forced induced system, cylinder compressor gear ratio on the engine performance. *Corresponding author: [email protected] © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). ITM Web of Conferences 15, 03002 (2017) DOI: 10.1051/itmconf/20171503002 CMES’17 The software used to develop the model was AVL Our model shows the entire route of the charge flow BOOST, which is a tool dedicated for 1D modelling of between the air inlet and outlet. The model reflects the piston internal combustion engines. This tool allowed us to process of fuel injection into the cylinders and map processes that occur in the combustion engine and combustion that occurs there. The calculation uses the parameters of the operating medium in the cylinder for the module for the two-stroke engine which consists of defined operating conditions and offered faster calculations (Fig. 1): an air inlet, a compressor connector, than in 3D models. However, we could combine 1- and 3D a compressor, an air cooler, intake and outlet ducts, models to obtain more information and more predictable cylinders (changes in cylinder volume), and Plenum- simulation results [10]. Carlucci, Ficarella and Trullo [11] created elements (of fixed volume). Preliminary research followed this approach to study the process of charge of 3D models of charge exchange enabled us to exchange in a two-stroke six-cylinder aircraft Diesel engine. introduce similar-to-a-target-solution dimensions of the The AVL BOOST also allows studying the correlation parts of the intake and outlet system including channels between the engine configuration and engine performance, in the engine block. To obtain maximum filling, other e.g. power, torque, fuel consumption, etc. elements of these systems were optimized. 2 MP1 TCP1 CO1 3 8 21 18 2 Model of the engine J4 J3 J5 SB1 MP2 MP3 20 19 22 The model of the engine is created in the AVL BOOST. MC1 17 16 It was a zero-dimensional physical modelling based on PL6 PL5 PL4 the principle of conservation of mass and energy. The E1 6 7 10 assumption is as follows: the 1D flow in the ducts means MP4 that the pressure, temperature and speed distribution C1 C2 C3 calculated from the dynamic equations of gas correspond 4 5 9 to average cross-sectional values in the duct. Flow losses MP5 PL1 PL2 PL3 due to phenomena that occur in the 3D space at 11 12 individual points in the engine are considered as specific 23 13 14 flow rates. This kind of model enables transient-state 24 15 1 MP6 research that successfully reflects varied flight J6 J1 J2 SB2 conditions, e.g. pressure, temperature. This model calculates the flows of air and fuel in the intake system Fig. 1. Model of the engine. and the cylinder including force inducing devices as well as combustion and the flow of exhaust gas to the The engine model is based on the mass flow in the environment. intake and outlet ducts, and refers to the equations for The principles of the model of the engine are as the isentropic circular cross-section flow. Mapping the follows: geometry of the intake ducts and other key elements is 1) a 1D model shows the length and diameter of performed with a view to obtaining as favourable as engine elements for the flow only; possible conditions for engine operation. The model also 2) a model of the two-stroke engine; is based on the assumption of mechanical radial 3) identical geometries of all three cylinders; compressors. To correctly model charge exchange, there 4) twice as large surfaces of piston bottoms than in are introduced the characteristics of window opening. reality to reflect the nature of the operation of the The model includes the mechanical centrifugal opposed-piston engine; compressor (radial), whose key function is to increase 5) geometric orientation of cylinders is neutral to the degree of engine filling (volumetric efficiency). their performance; Supplying more air into the engine (compared to 6) temperature of the component walls is constant; a naturally aspirated engine) contributes to obtaining 7) the system for charge exchange is symmetric; higher indicated mean efficient pressure. The use of 8) fuel is supplied directly to the combustion compressors in the two-stroke engine is necessary to chamber forming a mixture of a given composition. provide for charge exchange. The AVL Boost model of the engine required some The model of an air cooler is between the compressor simplifications due to the nature of the 1D mathematical and the Plenary element 1 placed before the cylinders. model. These are as follows: There are defined the dimensions, mass flow rate and 1) the flow of medium through the intake system and temperatures of the air inlet, coolant and air outlet. exhaust passes mainly round-section ducts; The compression ratio was defined by the correlation 2) the components of a large volume and a small of the cylinder volume and the combustion chamber and distance between the outlet and inlet sections to be the combustion chamber volume, which means that modelled by means of the Plenum (constant-volume theoretical coefficient of compression is specified so as element); to ensure highly efficient scavenging. 3) the fuel flow depends on mass flow rates and is The parameters of heat transfer into the cylinder automatically regulated to maintain a desired mixture walls were defined in line with the data from the composition.