Continuing advances in thermal and mechanical efficiency of engines is essential to improving fuel economy, with its beneficial effect on CO2 and pollutant emissions. Improvements to engine efficiency of about 10% should be possible within 20 years through developing combustion technologies. Diesel engines have a greater efficiency potential then gasoline, and increasing use is predicted in Europe to achieve low fleet average CO2 for light vehicles, although the future is likely to require multi-fuel capability. Gasoline direct injection is already available, although improvements are still needed to achieve good emissions performance. Technologies enabling downsizing of engines giving performance levels equivalent to today’s larger engine sizes are particularly important. Advances in variable transmissions and control will allow better matching to engine performance characteristics, allowing more energy efficient operation.

Vehicle and engine manufacturers must meet consumer demand for improved vehicle performance and drivability whilst achieving the challenge of reducing fuel consumption and emissions. Downsizing engines to obtain thermal and mechanical efficiency will only become attractive when driving performance is maintained relative to the larger power units they replace, and without additional cost. Transmission improvements, e.g. automated manual gearboxes, continuously variable transmissions etc, will also enhance performance characteristics, particularly when coupled to advanced control strategies.