Simulation and performance analysis of a spark ignition engine using gasoline and LPG as fuel

In this study, using the finite-time thermodynamics method, a simulation model has been created for Otto-cycle engines. In the model, it has been assumed that there are irreversibilities, heat, combustion, and friction losses, and also that the specific heat changes depending on the temperature, the cycle initial temperature changes depending on the residual gas temperature, and the working fluid is composed of the fuel-air-residual gas mixture. The effects of compression ratio, equivalence ratio, and stroke/bore ratio on engine performance were examined. Thermal efficiency, specific fuel consumption, specific fuel cost, and power density are used for performance analysis. Performance loss factors were used for engine heat balance. The characteristics of a single-cylinder spark-ignition engine have been used as a reference in the model. As a result of the numerical study, it was observed that when the volumetric efficiency decreased by 10% in LPG use, the power density decreased by 12%. Although the specific fuel consumption of LPG is higher than gasoline, the specific fuel cost of LPG is considerably lower than gasoline due to the LPG/gasoline price ratio. The loss of performance decrease as the compression ratio increases and the stroke/bore ratio decreases. Also, performance losses increase when the equivalence ratio is greater than 1. It is seen that LPG performance can be eliminated by increasing the volumetric efficiency or increasing the compression ratio. When the LPG/gasoline price ratio is 0.54, it is determined that the engine running on LPG is 24% more economical compared to working with gasoline. When the LPG/gasoline price ratio is 0.67, it has been observed that LPG has no economic advantage. Significant results have been obtained especially for engine designers.