Effect of Diesel-Ethanol-PPME (Pongamia pinata Methyl Ester) Blends as Pilot Fuel on CNG Dual-Fuel Operation of a CI Engine: A Performance-Emission Trade-Off Study

The major portion of todays natural gas dual-fuel engines use pilot amounts of diesel as the igniter fuel. However, it is found that dual-fuel operation of natural gas with pilot diesel poses problems, such as reduced brake thermal efficiency and increased hydrocarbon emission. The present experimental work explores the potential of compressed natural gas (CNG) under dual-fuel operation by utilizing two blends of diesel-ethanol-Pongamia pinata methyl ester (PPME) as pilot fuel. The blends, namely, D45E15B40 (45% diesel, 15% ethanol, 40% PPME) and D30E20B50 (30% diesel, 20% ethanol, 50% PPME) are selected on the basis of biodiesel-assisted miscibility of ethanol in diesel. It is found from the study that the pilot operation of D45E15B40 blend increases the brake thermal efficiency by 43.5% and 26.4% at 80% and 100% load conditions with CNG injection for 23?000 mu s, whereas D30E20B50 produces an increase of 51.7% and 46.5% under the same conditions in comparison with pilot diesel operation. The NOx emission from the engine is also decreased by 37.3% and 21.6% at 80% and 100% load conditions by D45E15B40 and 33.9% and 15.9% by D30E20B50 blend, as compared to pilot diesel operation. The trade-off study in the present work reveals encouraging aspects of D45E15B40 and D30E20B50 blends as it is found that pilot operation with these blends can stretch the usability range of CNG injection duration to 9000 mu s.