Effect of Fuel Injection Strategy on Nano-Particle Emissions from RCCI Engine

Increase in the air pollution has driven the research towards the cleaner combustion technology for reciprocating engines. To tackle the challenge of the trade-off between the NO_x and soot emissions from a conventional diesel engine, premixed low-temperature combustion (LTC) strategies are potential technologies. Among the LTC strategies, reactivity controlled compression ignition (RCCI) strategy has a better combustion phasing control along with higher fuel conversion efficiency and lower NO_x and soot emissions. The present study investigated the nano-particle emissions from RCCI engine fueled with a port injection of gasoline/methanol (low reactivity fuel) and direct injection of diesel (high reactivity fuel). The RCCI combustion experiments were performed on a modified single cylinder compression ignition engine with development ECU. The mass of injected fuel per stroke for the port as well as the direct injection is controlled through ECU. A differential mobility spectrometer (DMS) is used for the measurement of particle concentration along with their size-number distribution (particle mobility diameter range: 5 nm to 1000 nm). The effect of single and double injection strategy of high reactivity fuel on particle emission has been investigated at constant engine load for gasoline/diesel and methanol/diesel RCCI combustion. The results indicate that, in RCCI combustion strategy, the nucleation mode particles are in relatively higher concentration as compared to accumulation mode particles. Most of the particles emitted from the RCCI combustion are in size range of 5 nm to 300 nm, and large size particles (500 nm to 1000 nm) are also emitted in significant concentration. In double diesel injection strategy, the nucleation size particles are significantly higher as compared to the single diesel injection strategy the while accumulation mode particles are relatively lower. Results also depict that the diesel injection timings has no significant effect on the particle mass having a diameter less than 20 nm for gasoline/diesel RCCI operation. However, the mass of the particles above the 20 nm diameter range increased with advanced diesel injection timing.