Effect of Gasoline-Ethanol Blends on GDI Engine to Reduce Cost of Vehicle Ownership

A major challenge for combustion engine development is to optimize the engine for improved fuel economy, reduce greenhouse gases. Stringent CAFÉ and emission norms require the customer to pay higher capital on vehicles. To offset the cost of ownership- cheaper and alternative energy sources are being explored. Ethanol blend with regular Gasoline, and CNG are such alternative fuels. Reducing the consumption of Gasoline also helps India’s dependence on import of crude oil.

The study was carried on turbo-charged gasoline direct injection engine. The effect of ethanol on engine and vehicle performance is estimated and simulated numerically. The work is split into three stages: first the base 1D engine performance model was calibrated to match the experimental data. In parallel, vehicle level Simulink model was built and calibrated to match the NEDC cycle performance. Second, the thermal efficiency of the ethanol blend is calculated as a linear function of theoretical Otto cycle efficiency. The engine performance for varying compression ratio & ethanol gasoline blend is studied for vehicle level using a MATLAB code. Third, 1D code was run to simulate the high-speed exhaust temperature & low speed knock intensity, this is used a tool to select the compression ratio and ethanol blend. NEDC results of benchmark GDI engine has been used as baseline for vehicle model to determine cost of ownership of various blends with various Compression Ratios. Engine level performance simulation was done in commercial 1D code to study the effect of ethanol blend and compression ratio on knock, exhaust temperature and specific fuel consumption.

Combustion characteristics, friction losses have been taken to be same as the baseline engine. Cold start ability of various ethanol blends is not studied. Mechanical modifications required at engine and vehicle level to accommodate ethanol injectors are not considered. The effect of ethanol on aldehyde emission, cold start enrichment HC emissions, corrosion of engine components has not been considered.

The optimal combination of CR and blend is restricted due to re-fuelling frequency constraint, knock limit of engine and max exhaust temperature. Fuel blend of 30% and a CR of 12 gives 10% ownership benefit, while a fuel blend of 20% with a CR of 11 gives a 7% ownership benefit. This paper provides a novel system level approach using a 1D commercial code & 0D model to select engine and vehicle characteristics according to the user requirement