Fuel Formulation Effects on Gasoline Compression Ignition and Its Emissions

Abstract

This work presents an experimental investigation of fuel formulation effects on combustion processes, emissions, and engine performance when operating under gasoline compression ignition (GCI). The experiments presented here were primarily conducted in a single cylinder research engine that was modified from a production Cummins 6.7 QSB engine. Conditions were fixed for intake temperature, boost level, and back pressure providing an examination of performance at current production-like conditions. Additional work was done with a modified Cooperative Fuels Research engine to study the critical fuel equivalence ratio of the fuels to help understand differences in the results from the single cylinder engine testing. Within the Cummins single cylinder research engine, a total of five gasoline fuels were tested. For two of the fuels, seven test conditions were tested. For the other 3 gasoline fuels, as many test conditions as possible were tested with a limited quantity of fuel resulting in data at 4 or 5 test conditions. Gasoline with research octane numbers (RONs) of 54, 80, and 92 were tested to understand the effect of RON on GCI combustion, along with two additional fuels that had a RON of 80 but varied viscosity, temperature of which 90% of the fuel vaporizes (T90), and octane sensitivity. The results indicate that the gasoline with RON 54 exhibited too little resistance to autoignition to allow low temperature combustion (LTC) at the low load test condition, while LTC could be achieved with the higher RON fuels. On the other hand, the lower RON fuel performed better at the higher loads than the 92 RON gasoline. Overall, this study investigated the effects of fuel formulation on engine performance and emissions showing improvements in indicated specific nitric oxide emissions (ISNOx), and filter smoke number at all test conditions with every gasoline fuel compared to the diesel baseline. ISNOx was observed to decrease as much as 96% and smoke as much as 98%. Particle size measurements were also taken at several test conditions by a scanning mobility particle sizer (SMPS) allowing the number and distribution of particles to be analyzed. Results for particles indicated that the lowest RON fuel increased the number of particles at all test conditions while the higher RON fuels did not. The higher RON fuels in general had a lower number of particles than the diesel baseline though some test conditions had similar or increased numbers. In addition, all the fuels reduced the number of the smallest particles (<50nm) measured compared to the diesel baseline due to the fuels enabling a cleaner combustion process. Further work conducted looked at the three RON 80 fuels under identical conditions to better understand the effects their formulation had on the combustion process. During this testing it was found that the fuel formulations had important impacts on the emissions, and quantity of exhaust gas recirculation (EGR) needed to achieve the LTC mode, which in turn provided the most benefit in terms of reduction of ISNOx, smoke, and efficiency.