Combustion characteristics of various fuels during research octane number testing on an instrumented CFR F1/F2 engine

Abstract

The Cooperative Fuels Research (CFR) engine is the long-established standard for characterization of fuel knock resistance in spark-ignition internal combustion engines. Despite its measurements of RON and MON being widely used, there is little understanding of what governs the CFR octane rating for fuels of various chemical compositions compared to primary reference fuels (iso-octane and n-heptane). Detailed combustion characteristics were measured on a highly instrumented CFR F1/F2 engine during RON testing of fuels with significantly different chemical composition. The results revealed differences in the cylinder pressure and temperature conditions, as well as knocking characteristics.

Effects of fuel composition at varying air-fuel ratio on knock resistance during spark-ignition combustion

“…which they have a critical λ at less rich mixtures of 0.93 and 0.94, respectively. These findings agree with the values available in the literature, suggesting that blends including ethanol have a critical λ around 0.93, while iso-paraffinic fuels, PRFs, tend to have a higher knock intensity in the range from 0.90 to 0.88 (Kolodziej, 2017;Foong et al, 2017). It is interesting to see that when considering the PRFs, there is a trend of decreasing critical lambda with decreasing RON.…”

“…Table 1 shows the operating conditions of RON and MON tests. Overall, fuels are rated for MON at a higher intake mixture temperature and a higher engine operating speed than RON tests, representing more severe engine operating conditions (Kolodziej and Wallner, 2017). Therefore, during MON rating, the temperature of unburned gas is considerably higher at a given pressure than that under RON conditions.…”

“…However, the effect was not explicitly investigated, and insufficient understanding about the behaviour of these fuels on a commercial gasoline engine operating at a fixed air-fuel ratio was obtained. (Kolodziej and Wallner, 2017) investigated the effects of varying λ on the knocking characteristics and RON rating of a range of fuels all with a RON of 98 but with varying composition (achieved through different proportions of iso-paraffinic and aromatic species and also ethanol). It was found that the knock tendency of PRFs reduced significantly as the mixture moved towards stoichiometric, displaying greater knock resistance in comparison to aromatic and ethanol blends of the same RON values.…”

Determination of a most representative cycle from cylinder pressure ensembles via statistical method using distribution skewness

“…A summary of the instrumentation and engine geometry can be found in Table A3 in the Appendix and in previous publications. 17–19…”

“…A summary of the instrumentation and engine geometry can be found in Table A3 in the Appendix and in previous publications. [17][18][19] Finally, the last set of experiments was performed on a modern Gasoline Direct Injection (GDI) singlecylinder spark-ignition research engine. The engine head has a 40°pent roof design, with centrally located spark plug and DI injector.…”