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The operation of S.I. engines on lean or diluents containing gaseous fuel-air mixtures is attractive in principle since it can provide improved fuel economy, reduced tendency to knock and low NOx emissions combined with a possible improvement to the operational life of the engine. However, the overall flame propagation rates then tend to drop sharply as the operational mixture is excessively leaned or diluted with CO2 or N2. The paper presents experimental data obtained in a single cylinder, variable compression ratio, S.I., CFR engine when operated on a number of gaseous fuels and some of their mixtures. A gradual leaning of the operating mixture can affect adversely in turn, emissions of CO and unburned fuel and cyclic variation. The extent of deterioration in these operating parameters is shown to correlate well with the corresponding values of the combustion period, a key combustion indicator. Similar effects were observed when adding diluents to stoichiometric CH4-air mixtures.

Carbon monoxide (CO), carbon dioxide (CO2) and unburned hydrocarbon (UHC) are present in the exhaust gases of S.I. engines operated on pure hydrogen. These carbon-bearing species result from the oxidation of the lubricating oil and can be considered conveniently as natural tracers for indicating the lubricating oil consumption by combustion. Accordingly, such a novel approach can be employed to examine factors that affect engine oil consumption without the need to resort to more complex approaches. This contribution presents experimental results of oil combustion in a variable compression ratio single cylinder CFR engine when fueled with pure hydrogen established by determining the concentrations of CO and CO2 in the exhaust gas. The effects of changes in key operating variables that include equivalence and compression ratios, spark timing and the onset of knock on oil combustion are examined.

Hydrogen is normally produced through the steam reforming of fossil fuels, notably natural gas or their partial oxidation in oxygenated air. The products of these processes would normally produce the H2 in the presence of a variety of concentrations of CO, CO2, H2O and N2. There is increasing interest in employing such mixtures whether on their own or in mixtures with traditional liquid or gaseous fuels in S.I. engine applications so as to improve the combustion process and engine performance. The combustion characteristics in S.I. engines of gas mixtures that contain H2 and CO need to be established to provide key operational information, such as the variations in the combustion duration and the knock limits. This paper presents experimental data obtained in a single cylinder, variable compression ratio, S.I., CFR engine when operated in turn on CH4, H2, CO and their binary mixtures.

An engine is described that operates exclusively on stoichiometric H2-O2 mixtures with significant amounts of excess hydrogen circulated to effect controlled combustion of excessively rich mixtures within the engine cylinder combined with exhaust water condensation and removal. A two-zone quasi-dimensional model for predicting the performance and the likelihood of the onset of knock developed earlier for CH4-H2-air operation has been extended suitably to predict the approximate performance of this H2-O2 engine arrangement. A detailed chemical kinetic scheme for the oxidation reactions of H2-O2 mixtures is adopted in the knock prediction of this model. A prior knowledge of the variation of the combustion period needed for this predictive model was estimated through processing corresponding data for H2-air mixtures. The limited experimental results reported by Furuhama, et al., were used to validate the corresponding predicted values.