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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.

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.

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.

Knock characteristics of commercial LPG, with 83…87% propane and 9…15% alkenes have been investigated in a spark ignition engine for heavy duty vehicles. While knock characteristics of propane have been already studied, it was considered that there is at present a lack of information concerning a possible synergistic interaction in the end gas of propane with the alkenes, the second important component of LPG. Different conclusions existing on some issues, like the correlation between knock intensity and knock onset time on an individual cycle basis, emphasizing our insufficiencies in information, were also suggestive for our study. At last, special problems resulting from the need to make best use of the recorded pressure data, like the best way to isolating the high frequency component, were also addressed.

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.

An investigation has been done on the influence of small amounts of hydrogen added to hydrocarbons-air mixtures on combustion characteristics. The effect of hydrogen addition to a hydrocarbon-air mixture was firstly approached in an experimental bomb, to measure the laminar burning velocity and the shift of lean flammability limit. Experiments carried out with a single-cylinder four stroke SI engine confirmed the possibility of expanding the combustion stability limit, which correlates well with the general trend of enhancing the rate of combustion. An increase of brake thermal efficiency has been obtained with a reduction of HC emissions; the NOx emissions were higher, except for very lean mixtures.