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Occurrence of knock in spark ignition (SI) engines is usually suppressed by inhibiting auto-ignition of the fuel-air mixture. A steep increase in pressure by auto-ignition of the local mixture is thought to initiate the pressure oscillation, which results in knock. Therefore, in order to prevent knock, the strength of the pressure oscillation would be decreased by reducing the local heat release of the end gas. In this study, the oxidation reaction rate of the auto-ignition was attempted to be reduced by dilution of the mixture. The effect of mixture dilution on the strength of pressure oscillation, that is knock intensity, was examined using a rapid compression machine (RCM) and a single cylinder SI engine. The test result of compression ignition of homogeneous mixture using RCM showed that increase in dilution ratio could decrease the knock intensity even if the input heat increased and the auto-ignition timing advanced.

This paper presents the effects of a lubricant oil droplet on the start of combustion of a fuel-air mixture. Lubricant oil is thought to be a major source of low-speed pre-ignition in highly boosted spark ignition engines. However, the phenomenon has not yet been fully understood because its unpredictability and the complexity of the mixture in the engine cylinder make analysis difficult. In this study, a single oil droplet in a combustion cylinder was considered as a means of simplifying the phenomenon. The conditions under which a single oil droplet ignites earlier than the fuel-air mixture were investigated. Tests were conducted by using a rapid compression expansion machine. A single oil droplet was introduced into the cylinder through an injector developed for this study. The ignition and the flame propagation were observed through an optical window, using a high-speed video camera.

Furans such as 2-Methylfuran (2-MF) and 2,5-Dimethylfuran (DMF) can be produced from biomass sugars and offer superior properties for use in SI engines. This paper describes the study of the auto-ignition characteristics of furans and other biofuels using a rapid compression machine. Blending with PRF90 and RG, the auto-ignition suppression of 2-MF was almost equal to that of ethanol and larger than toluene, although the auto-ignition delay of pure 2-MF was shorter than that of ethanol and toluene. This was because 2-MF suppresses the cool flame reaction. Knock evaluation using a single-cylinder research engine also indicated that the addition of 2-MF improved the anti-knock properties as well as ethanol.

The chemical mechanism responsible for controlling ignition timing by using additives in HCCI has been investigated. Dimethyl ether (DME) and methanol were used as the main fuel and the additive, respectively. Fuel consumption and intermediate formation in the first stage (cool ignition) were measured with crank angle resolved pulse-valve sampling and exhaust gas analysis, where HCHO, HCOOH, CO, H2O2 and other species were detected as the intermediate. The effect of methanol addition retarding ignition is represented by an analytical model in which the growth rate of the chain reaction is reduced by the methanol addition.

Two different species measurements have been conducted for compression ignition of dimethyl ether in a motored engine. Crank angle resolved pulse-valve sampling with a resolution improvement scheme enabled to detect partial fuel consumption and formation of intermediate like H2O2 and HCHO at a cool ignition, as well as their total consumption at a hot ignition. FTIR analysis of exhaust gas in single cool ignition conditions confirmed formation of HCOOH and HCOOCH3 in cool ignitions. Results obtained in a range of equivalence ratio support the advantage of 2000 version of Curran et al. DME oxidation model.