The peak efficiency of modern spark ignited engines varies from 36% to 40% depending on the exact technology utilized. Most engines can achieve this peak efficiency for a limited operating region. Multi-speed transmissions allow the engine to operate closer to its most efficient operating regions for more significant portions of operation. In the case of hybrid powertrains, electric machines help in improving engine efficiency by adjusting operating speed and load. Engine shutdown during idle events and low loads is another avenue for improving the overall efficiency.
The choice of the ideal powertrain and component sizes depends on the engine characteristics, drive cycles and vehicle technical requirements. This study examines what type of powertrains will be suitable for more efficient engines that are likely to be available in the near future. Some of the new technologies achieve higher efficiency with a trade off on power or by accepting a more restrictive operating region. An appropriate powertrain choice can still enable such an engines to be a viable option for an automobile.
Using simulation tools, 11 different engine technologies are evaluated in this paper for their fuel saving potential. Vehicle models are created using advanced engine models with 5 powertrain choices for multiple vehicle classes. Sensitivity of fuel consumption to drive cycles is also evaluated. This analysis quantifies the fuel saving potential of each engine and powertrain combination to identify attractive solutions that could lead to affordable and efficient vehicles.