The paper presents some results regarding fueling an automotive diesel engine with compressed natural gas (CNG) in dual fuel mode; the purpose of the paper is to analyze the stability of combustion with help of the 5% and 90% of mass fraction burned (5% / 90%MFB) and of the coefficients of variability (COV) for in-cylinder maximum pressure; the use of CNG reduces the angle for 5% MFB with more than 10°CA (crankshaft angle) and extends with 2°CA combustion end of the entire quantity of fuel per cycle; the exhaust gases temperature grows with 7°C more than when engine runs with diesel only. © 2020, Politechnica University of Bucharest. All rights reserved.