Performance Evaluation of External Mixture Formation Strategy in Hydrogen Fueled Engine

Hydrogen induction strategy in ICE plays a vital role in increasing the power density and prohibiting combustion anomalies. This paper inspects the performance characteristics of cylinder hydrogen fueled engine with port injection feeding strategy (PIH2ICE). To that end, a one dimensional gas dynamic model has been built to represent the flow and heat transfer in the components of the engine. The governing equations are introduced first, followed by the performance parameters and model description. Air fuel ratio (AFR) was varied from stoichiometric limit to a lean limit. The rotational speed of the engine was also changed from 1000 to 4500 RPM; while the injector location was fixed in the midway of the intake port. The general behavior of hydrogen engine was similar to high extent to that of the gasoline engine with a reduction in the power density due to decrease in the volumetric efficiency. This emphasizes the ability of retrofitting the traditional engines with hydrogen fuel with minor modifications. The decrease in the volumetric efficiency needs to be fixed. INTRODUCTION In the recent days, there are two main issues regarding the fuels: availability and global climate change. The status of the availability of the fossil fuels is critical and the prices have been jumped to levels that never been reached before. Furthermore, the environmental problems are serious and the politics all over the world applied severe conditions for the automotive industry. Researchers, technologists and the automobile manufacturers have been increasing their efforts in the implementation of technologies that may well replace fossil fuels as a means of fueling existing vehicles. Hydrogen, as alternative fuel, has unique properties give it significant advantage over other types of fuel. However, the widespread implementation of hydrogen for vehicular application is still waiting several obstacles to be solved. These obstacles are standing in the production, transpiration, storage and utilization of hydrogen. The most important one is the utilization problems. Hydrogen induction techniques play a very dominant and sensitive role in determining the performance characteristics of the hydrogen fueled internal combustion engine (H2ICE) (Suwan, 2003). Hydrogen fuel delivery system can be broken down – in general into three main types: central injection (or "carbureted"), port injection and direct injection (COD, 2001). A comparison between these systems is beyond the present study. The port injection fuel delivery system (PI) injects hydrogen directly into the intake port, rather than drawing fuel in at a central point. Typically, hydrogen is injected into the port after the beginning of the intake stroke (COD, 2001). Hydrogen can be introduced in External Mixture Formation Strategy in Hydrogen Fueled Engine: Performance Evaluation 88 the intake port either by continuous or timed injection. The former method produces undesirable combustion problems, less flexible and uncontrollable (Das, 1990). But the latter method, timed PI is a strong candidate; and extensive studies indicated the ability of its adoption (Das et al., 2000; Das, 2000; Tang, 2002). The calling sounds for adopting this technique are supported by a considerable set of advantages. It can be easily installed only with simple modification (Lee et al., 1995); and its cost is low (Li and Karim, 2006). The flow rate of hydrogen supplied can also be controlled conveniently (Sierens and Verhelst, 2001). External mixture formation by means of port fuel injection also has been demonstrated to result in higher engine efficiencies, extended lean operation, lower cyclic variation and lower NOx production (Yi et al., 2000; Rottengruber et al., 2004; Kim et al., 2006). This is the consequence of the higher mixture homogeneity due to longer mixing times for PI. Furthermore, External mixture formation provides a greater degree of freedom concerning storage methods (Verhelst et al., 2006). The most serious problem with PI is the high possibility of pre-ignition and backfire, especially with rich mixtures (Kabat and Heffel, 2002; Ganesh et al., 2008). However, conditions with PI are much less severe and the probability for abnormal combustion is reduced because it imparts a better resistance to backfire (COD, 2001). Combustion anomalies can be suppressed by accurate control of injection timing and elimination of hot spots on the surface of the combustion as suggested by Lee et al. (1995). Verhelst (2005) recommended very late injection. With PI and stoichiometric mixture, operation engine loads up to indicated mean effective pressure (IMEP) of 9 bar can be achieved with optimized injection and valve timing (Meier, 1994). Knorr et al. (1997) have reported acceptable stoichiometric operation with a bus powered by liquid hydrogen. Their success was achieved by the following measures (1) formation of a stratified charge by timed injection of the hydrogen into the pipes of the intake manifold with a defined prestorage angle. At the beginning of the intake stroke a rich, non-ignitable mixture passes into the combustion chamber, then (2) injection of hydrogen with a relatively low temperature of 0-10 °C so that the combustion chamber is cooled by the hydrogen, and finally (3) lowering of the compression ratio to 8:1. One of the main conclusions drawn from the experimental study of Ganesh et al. (2008) was the possibility of overcoming the problem of backfire by reducing the injection duration. Sierens and Verhelst (2003) examined four different junctions of the port injection position (fuel line) against the air flow. Based on the results of their CFD model, the junction that gives the highest power output (Y-junction) was different from the junction that gives the highest efficiency (45deg junction). Finally a compromise was suggested. HYDROGEN ENGINE MODEL One-Dimensional Basic Equations Engine performance can be studied by analyzing the mass and energy flows between individual engine components and the heat and work transfers within each component. Simulation of one-dimensional flow involves the solution of the conservation equations; mass, energy, and momentum in the direction of the mean flow. Mass conservation is defined as the rate of change in mass within a subsystem which is equal to the sum of i and e from the system : sub= (1) Mohammed Kamil / Journal of Mechanical Engineering and Sciences 1(2011) 87-98 89 where subscript i represent inlet and subscript e exit. In One-dimensional flow the mass flow rate, , is defined by: