Combustion in diesel engines

Although the diesel engine is one hundred years old, it is constantly evolving, both as a result of a better understanding of the phenomena involved, and as a result of increasingly stringent demands for performance, low fuel consumption and reduced pollutant emissions. The performance and pollution levels achieved by engines recently launched on the market or under development would certainly have been considered unfeasible by the best diesel engineers 20 or 30 years ago.

Two main engine families are emerging:

• direct injection engines, which deliver lower fuel consumption and higher nitrogen oxide emissions. They are by far the most widely used in stationary applications, marine propulsion and engines for trucks and commercial vehicles. Their use in passenger vehicles is recent and still rare, due to the difficulty of operating them over a very wide rpm range;

• indirect-injection engines, which are currently in the majority for passenger car applications, thanks to their higher power-to-weight ratio, less costly injection system and good performance over a wide rpm range. Their higher fuel consumption has gradually led to their disappearance from industrial and truck applications.