Are diesel engines set to run rich?

Diesel engines are generally designed to run with a lean air-fuel mixture, meaning they use more air and less fuel compared to gasoline engines. However, under certain conditions, such as during heavy acceleration or cold starts, they may temporarily run richer to provide more power and reduce emissions. Overall, the efficiency of diesel engines comes from their ability to operate with excess air, leading to better fuel economy and lower emissions in typical driving scenariOS.