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The addition of hydrogen to the gasoline-air mixture may contribute significantly towards accelerating the combustion process, with the beneficial effects on engine performance and emissions. The present contribution describes the results of an experimental research where gasoline-air mixture was enriched with a Hydrogen Rich Gas (HRG) produced by the electrical dissociation of water. The HRG analysis shows the presence of hydrogen and oxygen together with some additional species. Experiments were carried out at engine light and partial load. Detailed results of the measurements are shown, namely engine torque and efficiency, exhaust emissions, cyclic variability, heat release rates and combustion duration. The possibilities of improving engine performance and emissions in correlation with the amount of HRG, the equivalence ratio and the engine operating condition are thus outlined.

The enhancement of the ignition discharge parameters has been proved as an efficient means to control homogeneous lean combustion, but its effects on the burning stages is still controversial. This work presents the results of a study about the effect of a moderate enhancement of the ignition systems on lean homogeneous mixtures combustion in a conventional engine. Three ignition systems were compared: a standard inductive system, (M1) a long duration glow discharge ignition system (M2) and a capacitor discharge system (M3). Effects on combustion, over a wide range of operating conditions were examined, based on the engine outputs and heat release analysis. Durations of the flame development stage and rapid burning stage were correlated to give a measure of the strength of the relationship between them. It was found that a positive influence on combustion efficiency and stability is exercised only at engine idle and light loads, M3 being the most efficient.

Cycle-to-cycle combustion variations in a spark ignition engine, lean operated, were approached with symbolic sequence statistics and return maps. The engine was operated with a gaseous fuel (LPG) and with a strong swirl induction generated, to give relatively advanced mixture homogeneity. A transition to nonlinear deterministic behavior was identified when the equivalence ratio was decreased to very lean conditions. It was thus found that the effect of residual gas fraction on communication between successive combustion events is weaker with an improved mixing. The deterministic effects, which are not controllable, can thus be removed to lower equivalence ratios and higher levels of residuals by an improved mixing within the cylinder.

The strategy of using hydrogen as an additive fuel for the diesel engine to improve exhaust emissions and combustion efficiency has been explored by many researchers in the last decade. The effects of pure hydrogen or the hydrogen-oxygen mixture generated by water electrolysis fueling car or heavy-duty diesel engines were studied, with notably different results. In the present work the supplementary fuel used was the gas produced by the water electrolysis process in a reactor with a special electrode design. Hydrogen-oxygen mixture or pure hydrogen was inducted with air in the engine intake manifold. Performance and emissions characteristics of a 3.6 liters tractor engine, naturally aspirated, were investigated for different operating conditions with gas substitution of diesel fuel up to 12% on energy basis.

An investigation of some engine knock characteristics of commercial LPG with 83…87% propane and 9…15% alkenes has been carried out on a spark ignition engine for heavy-duty vehicles. The best possibilities for defining the knock characteristics by the cylinder pressure record analysis were examined first. Some particularities of LPG autoignition in an engine were also put forth, considering the critical pressure and end-gas temperature, and the heat release rates due the critical reactions prior to autoignition; these particularities were compared with previous findings for pure propane. The problem of a possible correlation between knock intensity and the parameters used by an algorithm for combustion control was also approached.