To meet the requirements of strict CO2 emission regulations in the future, internal combustion engines must have excellent efficiencies for a wide operating range. In order to achieve this goal, various technologies must be applied. Additionally, fuels other than gasoline should also be considered.
In order to investigate the potential of the efficiency improvement, a SI engine was designed and optimized using 0D/1D methods. Some of the advanced features of this engine model include: High stroke-to-bore-ratio, variable valve timings with Miller cycle, EGR, cylinder deactivation, high turbulence concept, variable compression ratio and extreme downsizing. The fuel of choice was gasoline. With the proper application of technologies, the fuel consumption at the most relevant operating window could be decreased by approximately 10% in comparison to a state-of-the-art spark-ignited direct-injection four-cylinder passenger car engine.
Furthermore, the potential of methanol as fuel was investigated in the same manner. Thanks to its almost knock-free properties, the center of combustion could be kept at its optimum value of 8°CA aTDC for the whole engine map, even though compression ratio was increased by 4 units. Also, wall heat losses and losses through exhaust gas are kept low due to methanol’s lower combustion temperatures. As a result, an approximately 10% further increase in efficiency at low and medium loads was observed. At higher loads the efficiency improvement was even higher, reaching around 25% at full load.