THE EFFECT OF INJECTOR POSITION ON DIRECT INJECTION HYDROGEN ENGINE CONDITIONS

Transcription

1 Journal of Engineering Science and Technology Special Issue on 4th International Technical Conference 2014, June (2015) School of Engineering, Taylor s University THE EFFECT OF INJECTOR POSITION ON DIRECT INJECTION HYDROGEN ENGINE CONDITIONS M. H. ZULKEFLI 1, M. R. A. MANSOR 1,2, * 1 Department of Mechanical and Materials Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia 2 Centre for Automotive Research, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia *Corresponding Author: radzi@ukm.edu.my Abstract Direct injection concept is one of the solution for controlling the combustion process of gaseous fuel. This technology solved the volumetric efficiency problems for certain gaseous fuel such as hydrogen. The study was conducted to analyse the mixing of hydrogen and air in the combustion chamber of a direct injection hydrogen internal combustion engine. The idealness of the mixture was measured for different positions of the hydrogen injector, which are 0, 53 and 90 from the centre axis of the combustion chamber. The mixture formation is important because it safeguards the complete combustion of hydrogen in the combustion chamber. At the same time, the efficiency of the engine can be increased and the emission of nitrogen oxides (NOx) can be reduced. The model of the combustion chamber was built using the CATIA software and the mixing of hydrogen and air in the combustion chamber was analysed using the compressible flow simulation module. The results of the simulation were observed and compared; where it was found that the 0 position gave the largest mixing area that can lead to a better combustion process and an increase in output energy. This position of the hydrogen injector is thus proposed as the optimum design for the application in direct injection hydrogen internal combustion engines. Keywords: Hydrogen, Direct injection, Injector, CFD. 1. Introduction Hydrogen is a well-known energy carrier because it is one of the main solution for sustainable future to decrease the effect of greenhouse gas. In internal combustion engine, researchers are always trying to eliminate and minimize hydrogen drawbacks and maximize the efficiency in order to increase the feasibility of the on-board usage of hydrogen. 55

2 The Effect of Injector Position on Direct Injection Hydrogen Engine Conditions 55 The depletion of fossil fuel is another issue that should be addressed. Fossil fuels play a crucial role in the world energy market. The world s energy market worth around 1.5 trillion dollars is still dominated by fossil fuels [1]. The World Energy Outlook (WEO) 2007 claims that energy generated from fossil fuels will remain the major source and is still expected to meet about 84% of energy demand in It is expected, however, that the global energy market will continue to depend on fossil fuels for at least the next few decades. World oil resources are judged to be sufficient to meet the projected growth in demand until 2030, with output becoming more concentrated in Organization of Petroleum Exporting Countries. There is worldwide research into other reliable energy resources to replace fossil fuel, as they diminish; this is mainly being driven due to the uncertainty surrounding the future supply of fossil fuels [2]. Even though with the current situation where fossil fuel is sufficient, there is a need to find a new energy source to replace fossil fuel. At present, fossil fuel is still the most popular fuel used in internal combustion engines but it produced carbon dioxide (CO 2 ) emissions. Excessive emission of CO 2 is the reason behind the global warming phenomenon. The alternative fuel has to be easy to acquire and environmentally friendly. Researchers all over the world has conducted numerous research and one of the solutions is the usage of hydrogen to replace fossil fuel [3-7]. However, there are still a lot of problems that need to be addressed due to the abnormal combustion. The suppression of abnormal combustion in hydrogen engines has proven to be quite a challenge and measures taken to avoid abnormal combustion have important implications for engine design, mixture formation and load control. For sparkignition engines, three regimes of abnormal combustion exist: knock which is autoignition of the end gas region, preignition caused by uncontrolled ignition induced by a hot spot, premature to the spark ignition and backfire due to premature ignition during the intake stroke, which could be seen as an early form of pre-ignition, backfire is also referred to as back flash and induction ignition [8-11]. Nitrogen oxides (NO x ) will also be emitted from the combustion due to the high temperature of the fuel combustion [12]. Another matter that needs to be considered is that there is a limit to how lean the engine can be run. Because the calorific value per unit volume of hydrogen is lower than that of conventional hydrocarbon fuels, lean operations can significantly reduce the power output attributable to a reduction in the volumetric heating value of the air/fuel mixture [13]. Direct injection strategy will help to solve the volumetric efficiency problem. Hydrogen (H 2 ) is the lightest gas that exists in the atmosphere. It is also the most common element around especially in organic materials. Because of its abundance, hydrogen is claimed to be easy to obtain. Moreover, its combustion properties like flammability limit and energy produced also made hydrogen the better choice compared to other energy options like solar and hydro. The combustion process of hydrogen, which is similar to fossil fuel, makes it suitable to be applied to the current design of internal combustion engines without any major modification [13]. In this research, the effect of the hydrogen injector s position towards the hydrogen-air mixture will be analysed. Three injector positions will be examined throughout the research. Every position will be analysed on the blend of hydrogen and air in the combustion chamber, the pressure direction and also the diffusivity of

3 56 M.H. Zulkefli and M.R.A. Mansor hydrogen in air. The best position of the injector base on this research will be proposed at the end of the analysis. 2. Methodology The research was carried out through computer simulations. The simulation was done by simulating the mixing process of hydrogen and air in the combustion chamber. STAR-CD was used for the three-dimensional problem solving. Four steps were involved in the whole process. They were CAD modelling, preprocessing, engine combustion simulation process and postprocessing. Table 1 shows the specification of the engine used for the case setup in this study. The injector type is a single-hole direct injection high pressure gaseous injector CAD modelling Type of engine Table 1. Engine specification. No. of cylinder 4 Bore x Stroke Displacement Type of injector CAMPRO 1.6 DI 77 mm 88 mm 1597 cc 1.0 mm 1 The combustion chamber was designed using the CATIA software. The combustion chamber was designed according to the specification of a CAMPRO 1.6L engine. The bore and stroke are 77 mm x 88 mm. The CAMPRO 1.6L engine was initially designed for petrol use with a port injection method. Some alterations were done on the engine in order to operate with direct injection strategy [14]. Injector was attached to the cylinder head in order to supply direct injection fuel to the combustion chamber. Figure 1 shows the three positions of injector that were chosen for the analysis. Those positions are 0, 53 and 90 from the central axis of the combustion chamber. The reasons behind the selection of those positions are that 0 from the central axis of combustion chamber is the common position for injectors of diesel and gasoline direct injection engines. 53 from the central axis of combustion chamber is the position for injectors of compressed natural gas (CNG) direct injection proposed by previous researchers [15]. Whereas 90 from the central axis of combustion chamber is the common position used by researchers for comparison purposes. The injection timing was modelled to inject the fuel at 30 BTDC, the standard timing for fuel injection for reciprocating engines. Fig. 1. Fluid body models for 0, 53 and 90 from the central axis of combustion chamber.

4 The Effect of Injector Position on Direct Injection Hydrogen Engine Conditions Engine combustion simulation process The engine combustion simulation process involves mathematically solving the physics model according to the boundary conditions that have been set. The simulation time, time-step and number of iterations are shown in Table 2. The overall time needed for a stroke to be complete under an engine speed of 1200 rpm is 25 ms. However, the simulation is also constrained by the number of iterations. 50 iterations with a time-step of 0.25 ms is set for this analysis. To obtain a more precise result, a shorter time-step can be set but for this study, 0.25 ms time-step is acceptable. Table 2. Time domain simulation. Simulation time Simulation time-step Number of iterations ms 0.25 ms Postprocessing is the process whereby the results from the calculations of the engine process are shown. Postprocessing simulates the results in term of graphical view to give more understanding for the user to interpret the results in the next section. 3. Results and Discussion The mass fraction of hydrogen and air represent the mixing area in the combustion chamber. Figure 2(a) shows a large mixing area of hydrogen and air. It shows that hydrogen and air were well mixed in the combustion chamber compared to Fig. 2(b) and Fig. 2(c). Figures 3(a) and 3(b) show the mass fraction of air and also shows the decent mixing areas for 0 and 53 positions compared to the 90 position. Fig. 2. Mass fraction of hydrogen for 3 positions of injector. Fig. 3. Mass fraction of air for the three positions of injector.

5 58 M.H. Zulkefli and M.R.A. Mansor Figure 4 shows the effective mass diffusivity of air which represents the portion of combustion chamber that allows hydrogen to diffuse in air. The large area of effective diffusivity of air shows the area that hydrogen may diffuse in. If we compared, hydrogen injector positioned at an angle of 0 and 90, Fig. 4(a) and Fig. 4(c) give the air mass diffusivity greater than at the 53 position. Wider diffusivity indicate more air to enter and mixed with hydrogen. Air mixed in hydrogen will establish a homogeneous mixture. But the speed of the piston movement and a short mixing time does not allow hydrogen mixed with air in homogeneous condition. Therefore, effective mass diffusivity is important especially when the engine principle allows the ignition delay. Fig. 4. Effective mass diffusivity of air for the three positions of injector. The temperature of the combustion chamber is shown in Fig. 5. The temperature is strictly limited to not more than 800 K. This is because the autoignition temperature of hydrogen in air is around 800 K. If the temperature exceed the autoignition temperature, the mixture will combusts before spark ignition timing. This phenomenon is called engine knock. Moreover, if the mixture ignite before the intake valve of the engine closes, it will result in backfire and decreased the efficiency of an engine. For hydrogen injector positioned at an angle of 0 and 53, Fig. 5(a) and Fig. 5(c), the flame propagate towards the combustion wall is uniform. Since the combustion occurs away from the wall, heat loss to the wall can be minimized. Fig. 5. Temperature in combustion chamber for the three positions of injector. Another aspect to be analysed is the pressure induced by the injection of hydrogen into combustion chamber. Tables 3, 4 and 5 show the values of pressure exerted in a three dimensional axis for each injector position of 0, 53 and 90 respectively. The best injection is supposed to induce uniform pressure in all directions.

6 The Effect of Injector Position on Direct Injection Hydrogen Engine Conditions 59 To propose the best location of the hydrogen injector for the application in the direct-injection hydrogen internal combustion engine (DI H 2 ICE), the criteria of analysis need to be clarified. The mixture should cover a large portion of the mixing area. Larger area of mixing shows that the hydrogen and air are well mixed in the combustion chamber. A small area shows that the mixing was not too well mixed in the combustion chamber. A mixing area that is too small may also lead to unburned mixtures because the mixture may not reach the flammability limit. Table 3. Pressure induced by the hydrogen injector at 0 from the central axis of combustion chamber. Pressure Direction Value (N) x-axis y-axis z-axis Table 4. Pressure induced by the hydrogen injector at 53 from the central axis of combustion chamber. Pressure Direction Value (N) x-axis y-axis z-axis Table 5. Pressure induced by the hydrogen injector at 90 from the central axis of combustion chamber. Pressure Direction Value (N) x-axis y-axis z-axis The pressure is supposed to be uniform in the combustion chamber. This is because a uniform pressure can ensure that the flame from combustion will propagate uniformly throughout the combustion chamber. This in turn can produce a uniform pressure on the piston surface and optimise the output power to the crankshaft. Effective diffusivity represents the area that hydrogen may diffuse in the air. In this particular research, effective diffusivity may bring minimum effect to the mixing process, since hydrogen diffuse quickly into air. However, effective diffusivity is important for the improvement of the engine, especially when there are ignition delays. The temperature of the combustion chamber must not exceed the autoignition temperature of hydrogen. Exceeding the temperature would result in engine knocks. Engine knock should be eliminated from the operation of engine because it can damage the engine s components and lower the output power of the engine. According to the definition of each criterion, the best position of the injector that can lead to the optimum mixture is at 0 from the axis of combustion chamber. At this position, the mixing area is the largest. Additionally, the temperature should not exceed the autoignition temperature. The effective diffusivity area is also large

7 60 M.H. Zulkefli and M.R.A. Mansor and can lead to improvements of the engine. Even though the pressure is not uniform, the direction of the pressure shows that the injection can penetrate deeper in the combustion chamber. 4. Conclusions All three positions do not exceed the autoignition temperature under the operational condition of 25 ms of simulation time. The position of 0 gives the largest mixing area. This can lead to more combustion processes and increases the output energy. The position of 90 shows the smallest mixing area because the position is far away from the combustion chamber. Effective diffusivity is large for the positions of 0 and 90. This shows the capability of hydrogen to diffuse in higher mass of air. Even though there is minimum effect on the mixing process for this particular case, this study may lead to more improvements for the engine. Both positions of 0 and 53 show the uniform direction of pressure. This can ensure that the flame from the combustion process propagate uniformly throughout the combustion chamber. The best position for the application of direct-injection hydrogen internal combustion engine is the position of 0 from the axis of combustion chamber. This position gives the largest mixing area and effective mass diffusivity of air and the flame can propagate uniformly for the entire combustion process. Acknowledgment The authors are thankful to the Ministry of Education Malaysia for supporting this study under the grants FRGS/2/2013/TK01/UKM/02/1 and GGPM References 1. Goldemberg, J. (2006). The promise of clean energy. Energy Policy, 34, Shafiee, S.; and Topal, E. (2009). When will fossil fuel reserves be diminished? Energy Policy, 37(1), Huang, Z.; Wang, J.; Liu, B.; Zeng, K.; Yu, J.; and Deming Jiang, D. (2007). Combustion characteristics of a direct-injection engine fueled with natural gashydrogen blends under different ignition timings. Fuel, 86(3), Mohammadi, A.; Shioji, M.; Nakai, Y.; Ishikura, W.; and Tabo, E. (2006). Performance and combustion characteristics of a direct SI hydrogen engine. International Journal of Hydrogen Energy, 32(2), Karim, G.A. (2003). Hydrogen as a spark ignition engine fuel. International Journal of Hydrogen Energy, 28(5), Mansor, M.R.A.; and Shioji, M. (2013). Characterization of hydrogen jet development in an argon atmosphere, Zero-Carbon Energy Kyoto 2012, Mansor, M.R.A.; Samiran, N.A.; Mahmood, W.M.F.W.; and Raja, N.A. (2014). Effect of Injector Nozzle Design on Spray Characteristics for Hydrogen Direct Injection Engine Conditions. Applied Mechanics and Materials 660,

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