Hydrogen enrichment may offer enhanced performance of internal combustion engines. Hydrogen's high specific energy, wide flammability limits, and high flame speed are all desirable traits that can potentially enhance combustion. However, hydrogen's low energy density and its need to be produced from another energy source pose significant challenges for implementation. Hydrogen enrichment involves co-firing of hydrogen and another primary fuel. The hydrogen can be aspirated through the intake manifold via fumigation or injected at the port or cylinder with the primary fuel. The effect of hydrogen fumigation in diesel engines has been studied to some degree but is not fully understood. In this research, a single-cylinder four-stroke direct-injection diesel engine was modified for hydrogen fumigation and was instrumented to monitor combustion related performance parameters. This engine is representative of low-cost systems that are widely used in developing nations for agricultural and other low power applications. A factorial design of experiments was implemented to study the effects and interactions of hydrogen fumigation flow rate, injection timing, and diesel fuel flow rate on part-load engine performance. At relatively low energy fractions, hydrogen was found to have statistically insignificant effects on brake torque and indicated mean effective pressure, leading to modest decreases in brake thermal efficiency. Exhaust gas temperature increased with hydrogen enrichment. The coefficient of variance of indicated mean effective pressure decreased with hydrogen enrichment, and visible changes to the in-cylinder pressure trace were observed, particularly when injection timing was retarded. The results of this investigation show that for this specific configuration, hydrogen enrichment is not beneficial to the combustion process. The marginal improvements in coefficient of variance and changes of in-cylinder pressure cannot justify the decrease in thermal efficiency of the engine.
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