Use of CNG and Hi-octane gasoline in SI engine: a comparative study of performance, emission, and lubrication oil deterioration

The search for alternative fuels (i.e. other than gasoline) is a continuous area of research. In the present work, a comparative study has been conducted by employing a liquid ((G)(97)) and a gaseous (CNG) fuel in a spark ignition engine. Engine performance, emission. and lubrication oil condition tests have been performed for two fuels by varying operating conditions according to comprehensive sampling plans in each area. Speed was incrementally increased in two phases over the investigated range of rpm for brake power and peak torque. For specific fuel consumption and emission tests, speed was increased through a uniform increment rises over the investigated range of rpm. Lubrication oil samples have been collected over 120 h of engine running with topping for drain out quantity and tests were performed as per ASTM standards. (G)(97) showed an improved performance, i.e. 28.8% increase in case of brake power as compared to CNG; however, CNG outperformed (G)(97) in case of emission contents and brake-specific fuel consumption (17.2% decrease). Moreover, emission data were fitted to Weibull distribution to ascertain the adequacy for a 95% confidence interval. Furthermore, wear debris (Iron (Fe), aluminum (Al), copper (Cu), chromium (Cr)), lubrication oil condition (kinematic viscosity, flash point and total base number (TBN), and additives depletion (zinc (Zn), calcium (Ca)) showed a visible improvement in case of CNG as compared to (G)(97). Lubrication oil analyses depicted 4.9%, 9.5%, and 3.2% reduction in viscosity, flash point, and TBN for (G)(97), respectively. However, Fe, Al, and Cu decreased by 12.9%, 29.1%, and 37.7% for CNG, respectively. Mechanisms involved in combustion and lubrication oil deterioration have also been discussed for two fuels.