1. ABSTRACTThe emission characteristics of compression ignition (CI) engines running on biodiesel during transient operating conditions, which is the most usual case in urban and extra-urban transportation, have rarely been investigated. In the present study an experimental investigation on emission characteristics of a CI engine has been carried out both under steady state and transient operating conditions. The experimental work has been carried out on CI engine, which is integrated with transient testing facility. This facility is capable of varying the engine speed and load over a given time period. To measure the engine emissions, an emission analyzer has been used to measure CO₂, CO, THC, and NOx emissions. The fuels used in the analyses are 25% (25B) and 100% (100B) of biodiesel blend and diesel. The series of the transient events studied are speed changes from 900 to 1200rpm, 1200 to 1500rpm and 1500 to 1800rpm over a time period of 4 seconds each. These tests were performed at a constant load of 105Nm, 210Nm, 315Nm and 420Nm. The transient test results have shown that the emissions of CI engine running on biodiesel were reduced by up to 17%, 52% and 38% for CO, CO₂ and THC emissions respectively as compared to diesel fuel. However, the NOx emission was seen to be 17% higher for engine running on biodiesel than that on diesel during transient conditions.