Numerical Simulation Of The Low-temperature Combustion Characteristics Of A N-butanol-gasoline Engine

The combustion characteristics of a homogeneous charge compression ignition(HCCI) engine were influenced by n-butanol volume fraction in n-butanol-gasolineblend. The increase in the maximum heat release rate is a major issue to extend theupper load limit of the HCCI engine. Therefore, smoothing the heat-release rates athigh loads is the key to apply HCCI combustion to production engines. In this thesis,a3-dimensional computational fluid dynamics model coupled with a reducedn-butanol-gasoline chemical kinetics mechanism was constructed and the effect ofmixture preparation through different fuel injection approaches on the distribution ofmixture components and temperature in the cylinder was simulated for alow-temperature combustion n-butanol-gasoline engine fuelled with0%,30%and48%n-butanol by volume, respectively. The following conclusions can be drawn:With the increase of n-butanol volume fraction in n-butanol-gasoline blend forthe cases of homogeneous n-butanol-gasoline mixture formed in the intake ports,autoignition timing advances, combustion duration decreases and the maximum rateof pressure rise increases.In the case of gasoline port injection with n-butanol direct injection to preparemixture, autoignition first occurs in the zone where the state of the mixture is betweenhigh temperature and high fuel concentration caused by fuel stratification. At fixedn-butanol volume fraction in the blend and the mass of fuel injected in a cycle, withthe delay of n-butanol injection timing, the stratification of fuel and temperature in thecylinder increases, autoignition timing retards, resulting in long combustion duration.For the blend with48%n-butanol by volume, autoignition timing, combustionduration and the maximum rate of pressure rise are more sensitive to the directinjection timing of n-butanol.For the injection with n-butanol-gasoline blend at opened intake valve, thestratification of fuel and temperature in the cylinder is higher for the case withasymmetric port fuel injection as compared to the case with symmetric port fuelinjection. The former can retard autoignition timing and prolong combustion duration,resulting in a significant reduction in the maximum rate of pressure rise and themaximum cylinder pressure. With the increase of n-butanol volume fraction in the blend, asymmetric port fuel injection has slightly effect on retarding autoignitiontiming while it prolongs combustion duration. Furthermore, asymmetric port fuelinjection can reduce the maximum rate of pressure rise and the increasing tendency ofin-cylinder peak pressure for the blend with48%n-butanol by volume.For n-butanol-gasoline blend, the maximum rate of pressure rise and themaximum pressure increase with the increasing of n-butanol volume in the case ofsingle direct injection. Dual pulse direct fuel injection can change the stratification oftemperature and fuel components in the cylinder. The ratio of the mass injected in thesecondary injection to the total mass injected in a cycle has much effect on heatrelease rate than the secondary injection timing. With the increase of n-butanolvolume in the blend, dual pulse direct injection has an important role on thestratification of temperature in the cylinder and autoignition timing, but has slightlyeffect oncombustion duration.