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A LPG fuelled, spark ignition engine for heavy duty vehicles has been developed from a Diesel DI engine which is currently in production. The development concept was based on the targets of obtaining output performances by LPG fuelling comparable with those of the original Diesel engine under full load conditions to be achieved with relatively simple technologies. A conventional mixer system with closed-loop control was consequently used for the LPG fuel supply system, operating at λ = 1.0. A systematic optimization was applied in the areas of the compression ratio, combustion chamber configuration, intake swirl ratio and plenum configuration, spark timing, in view of reaching high output performances and knock phenomena control. The results of optimization were higher torque and equal fuel conversion efficiency (at full load) in comparison with the original Diesel version of the engine.

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.

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.