The experimental work presents a comparative study of performance and emission using Pongamia pinnata methyl ester (PPME) and Diesel as pilot fuel in a Cl (compression ignition) engine with compressed natural gas (CNG) as the primary fuel. The results show that PPME CNG dual fuel operation is more effective than Diesel CNG dual fuel operation in improving the performance and emission characteristics of the engine. CNG is found to share higher quantity of input energy with PPME pilot operation than pilot Diesel operation. Low amount of CNG injection also increases the brake thermal efficiency of the engine. PPME CNG operations with low amount of CNG injections are also more instrumental in reducing CO (carbon monoxide) emission and smoke opacity than Diesel CNG operations. NO emission from the engine is found to increase a bit for PPME CNG operations in comparison to Diesel CNG operation. PPME CNG operation is also more effective in reducing hydrocarbon emission than Diesel CNG operations. The study also shows that CNG injected at 100 ATDC (after top dead center) for a duration of about 4500 mu s with PPME as pilot fuel can produce better performance and emission signatures than Diesel CNG operation. The tradeoff study also consolidates the fact that PPME CNG dual fuel operation is instrumental in resolving the high performance low emission paradox. (c) 2014 Elsevier Ltd. All rights reserved.