Knock and Combustion Characteristics of CH4, CO, H2 and Their Binary Mixtures

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. The dependence of the knock limited equivalence and compression ratios of CO on the extent of presence of H-bearing additives such as CH₄, H₂ or H₂O is presented and discussed. It is shown that the knock limits of dry CO deteriorate very significantly with the presence of relatively small amounts of CH₄, or H₂. The effects of the presence of some small amounts of H₂O with pure CO were also shown to vary significantly, yet to a lesser extent than that encountered with CH₄ or H₂ addition. The variation in the combustion duration with the increasing presence of CH₄ with CO shows a similar trend to that of the knock limited equivalence ratio. Such data can serve as the experimental basis for the validation of the corresponding values of predictions of the engine performance including knock limits.