Diesel Engine Notes From SAE (Belated)
The projected solution to improve diesel engine efficiency is to use hybrid power to bring about a 15% to 20% improvement, engine stop/start to eliminate idling will save about 6 to 7%, and 10 to 15% optimization and electrification of auxiliaries, as well as another 7% to 10% improvement from downsizing the engine and downspeeding RPM.
Thirty years ago maximum injection pressure was 500 bar. Now it's close to 2,000 bar and direct injection allows for higher compression ratios, more torque and higher knock thresholds.
In addition to consuming less fuel, downspeeding results in lower friction and wear, and also keeps the weight down. Engines need forced induction for torque, and sequential turbos are even better to eliminate the turbo lag of one big turbo.