Effect of Injection Parameters and EGR on the Particle Size Distributions and Exhaust Emissions for Diesel and Biodiesel Fuels in CRDI Engine

Biodiesel is considered one of the most promising alternative fuels to petrol fuels. In this study, an attempt has been made to investigate and compare the effect of fuel injection pressure, injection timing, and exhaust gas recirculation (EGR) ratio on the particle size distributions and exhaust emissions of the diesel and biodiesel produced from waste cooking oil (WCO) used in a common rail direct injection (CRDI) diesel engine. The engine tests were conducted at two injection pressures (800 and 1600 bar), two injection timings (25 and 5 deg before top dead center (bTDC) and three EGR ratios (10%, 20% 30%) at a constant fuel injection energy per stroke and engine speed (1200 r/min). The results indicated that carbon monoxide (CO) and hydrocarbon (HC) emissions of biodiesel were slightly lower, but nitrogen oxide (NOx) emissions were slightly higher, than those of diesel fuel under most operating conditions. Biodiesel engine emitted lower soot particle concentration than diesel engine. With the increase of injection pressure, CO and HC emissions were slightly decreased, NOx emissions were increased and soot particle concentration were reduced. Injection timing had no evident influences on CO and HC emissions, but NOx emissions were dramatically decreased with the retard of injection timing. The effect of fuel injection timing on soot particle concentration was not clear and consistent between diesel and biodiesel fuel. With the increase of EGR ratio, CO and HC emissions were evidently increased, NOx emission were decreased, and soot particle concentration were evidently increased due to the addition of EGR caused the particles to agglomerate and form larger size particles.