The most important process to ensure proper combustion is the perfect mixture of fuel and air in addition to many other variables.

Diesel fuel is a menagerie of hydrocarbon molecules that differ in size and shapes. Short molecules generally burn very quickly, causing temperature and pressure inside an engine to rise in a dramatic spike. That creates engine knock and emissions of nitrous oxide pollution. Meanwhile, longer hydrocarbons burn more slowly and incompletely, which raises exhaust temperature and leaves remnants of hydrocarbons to contribute to soot and other forms of pollution.