Influence of direct injection timing and mass of port injected gasoline on unregulated and nano-particle emissions from RCCI engine

The study aims to experimentally characterize the nano-particle emissions and un-regulated (i.e., saturated and unsaturated hydrocarbons and formaldehyde emissions) emissions. Present study experimentally investigates the effect of high reactivity fuel injection timings and port-injected-fuel mass on nano-particle and unregulated emissions in the gasoline-diesel RCCI engine. Additionally, empirical correlations are developed using experimental data for the estimation of particle emission characteristics. An automotive single cylinder diesel engine is modified for an in-cylinder blending of port-injection of gasoline during suction stroke and direct-injection of diesel fuel during the compression stroke. The experiments are performed on a modified engine for various diesel injection timings and port-injected gasoline mass using development electronic control unit (ECU). Nano-particle and unregulated emissions are measured using electrical mobility based particle-sizer and Fourier-transform infrared spectroscopy analyser respectively. Combustion analysis is performed by in-cylinder pressure measurement. The experimental data of nano-particle and combustion characteristics are used for the development of empirical correlation using a multivariable regression technique for determining the particle number characteristics. The parameters - premixing ratio, start of injection of diesel, and a novel parameter defined as premixed fraction of total heat release are used for the development of empirical correlations and found a good correlation for estimating the nano-particle emission characteristics. Results also indicate that advanced direct injection timing and increase in the port-injected gasoline mass leads to higher particle emissions as well as saturated, unsaturated hydrocarbon and formaldehyde emissions.