diesel

Diesel is a fuel derived from petroleum and used in diesel engines. It has a relatively high energy density and a broad boiling range. The fuel's ignition quality is described by the cetane number, with higher values indicating shorter ignition delay in compression-ignition engines. Diesel commonly contains sulfur, though content is regulated and varies by market; ultra-low-sulfur diesel is standard in many regions.

Diesel engines are compression-ignition internal combustion engines in which air is compressed to a high pressure and the fuel is injected, igniting from the high temperature of the air. They are noted for higher thermal efficiency and fuel economy compared with many gasoline engines, which makes them common in heavy-duty transportation, maritime vessels, and power generation. They can operate on various diesel fuels including conventional petrodiesel, biodiesel, and synthetic diesel.

Diesel derives its name from Rudolf Diesel, who developed the engine and demonstrated the concept in the 1890s. He designed an engine that could ignite fuel by compression rather than by spark, enabling higher efficiency. The first successful demonstrations occurred in 1897, and the technology rapidly spread.

Biodiesel is a renewable option made from vegetable oils or animal fats and can be used in some diesel engines with minimal modifications. Synthetic diesel, produced from natural gas or coal via Fischer–Tropsch synthesis, is another alternative in some markets. Ongoing research seeks to reduce emissions and improve efficiency, including advanced fuel formulations and electrified powertrain complements.

Modern diesel engines are subject to emissions standards that limit NOx, particulates, and other pollutants. Technologies such as exhaust-gas recirculation, diesel particulate filters, and selective catalytic reduction with urea are commonly employed to meet standards. Public concerns about health and climate impacts have influenced shifts toward cleaner fuels and alternatives in many regions.