Effect of dwell period between main and pre injection on NOx and smoke emission from CRDI diesel engine fueled with Biodiesel blend

Abstract

Diesel engines are very much widely used as a power source in industrial, transportation and power generation sectors due to their higher efficiency and better fuel economy. But the major drawback of diesel engines is its higher emissions of NOx and smoke due to heterogeneous combustion that exists in diesel engines. In general the emissions like HC and CO from diesel engines are less compared to gasoline engines because they run mostly with lean mixtures. Due to contradicting requirements for the reduction of NOx and smoke, the tradeoff between NOx and smoke emission without compromising fuel economy is a big challenge being faced by automotive industries and researchers in the field. Also to have sustainable civilization, there is a need to find eco friendly and renewable alternative fuel to petro diesel to conserve fast depleting petroleum resources and to minimize environmental pollution. Biodiesel produced from non-edible feed stock is found to be a good alternative to petro diesel. It is observed that the formation of NOx is very much dependent on the peak temperature in the combustion chamber. Various types of techniques are being tried by the researchers to reduce high NOx emission from usage of biodiesel blended fuel in diesel engines. The techniques used are like dilution using EGR, injection of water, retardation of injection timing etc. With the development of CRDI systems split and multiple injection strategy attracting the attention of researchers as a promising technique in reducing the NOx emissions. In this work an attempt is made to study the effect of dwell between pilot and main injection in a multiple injection strategy of Pilot-Main-Post injection while retarding main injection. In this multiple injection strategy of three injection pulses the pilot fuel quantity is fixed as 10% of total fuel injected, post injection fuel quantity is fixed as 0.5 mg. The dwell between pilot and main was varied at different main injection timing. The post injection is closely coupled with main injection with a dwell of 3 CAD. The main injection timing along with pilot and post was retarded from the recommended 23^o bTDC in steps of 3 degrees.  At all main injection timing the dwell of 10 CAD observed to be the best for smoke reduction, where as 20 CAD is better for NOx reduction. In overall Dwell 10 CAD is better for trade off between NOx and Smoke.