Diesel engine

Diesel engine
Name	Diesel engine
Caption	Cutaway view of a modern turbocharged diesel engine

Diesel engine. The diesel engine is a type of internal combustion engine invented by Rudolf Diesel in the late 19th century. It operates on the principle of compression ignition, where air is compressed to a high temperature and fuel is then injected, causing spontaneous combustion. This design is renowned for its high thermal efficiency and torque output, making it dominant in heavy-duty applications worldwide.

History

The concept was patented by Rudolf Diesel in 1892, with his first successful prototype demonstrated at the Augsburg works of MAN SE in 1897. Early development faced challenges, but adoption grew for stationary power and marine use, such as in submarines during World War I. The Caterpillar Inc. company helped popularize it in heavy machinery, while Robert Bosch's refinement of the fuel injection system was critical. Its use expanded dramatically in World War II in vehicles like the Soviet T-34 tank and post-war in commercial trucks and railway locomotives. The oil crisis of 1973 further cemented its role in transportation due to its fuel economy.

Operating principle

The engine operates on the Diesel cycle, distinct from the Otto cycle used in gasoline engines. Air alone is drawn into the cylinder (engine) and compressed by the piston at ratios typically between 14:1 and 25:1, dramatically increasing its temperature. Near top dead center, diesel fuel is injected at high pressure by an injector into the hot air, causing it to ignite without a spark plug. This combustion forces the piston down, converting chemical energy to mechanical work via the crankshaft. The process relies on precise control of injection timing and air-fuel ratio.

Design and components

Key components include a robust engine block often made of cast iron to withstand high compression pressures. The cylinder head houses the inlet valve and exhaust valve, controlled by a camshaft. Modern engines use a common rail direct injection system developed by companies like Fiat Group and DENSO. Turbocharging, pioneered by Swiss engineer Alfred Büchi, and intercoolers are standard to increase power density. The fuel pump, historically a unit injector or distributor pump, pressurizes fuel. Other critical parts are the piston ring, connecting rod, and crankshaft within a crankcase.

Types and applications

Engines are categorized by cycle: two-stroke designs, used in large marine propulsion like those from Wärtsilä, and four-stroke designs, common in automotive use. Cylinder arrangements include inline engine, V engine, and opposed-piston engine configurations. They power a vast range of equipment: heavy-duty trucks from Volvo Group and Daimler Truck, agricultural tractors from John Deere, construction equipment from Komatsu, and electric generators for power stations. They are also prevalent in rail transport, naval vessels like the Royal Navy's ships, and some passenger cars, notably models from Volkswagen Group.

Performance and efficiency

A major advantage is superior brake thermal efficiency, often exceeding 40% and reaching over 50% in large marine engines, compared to about 30-35% for typical gasoline engines. This results from high compression ratio and lean air-fuel mixture operation, reducing pumping losses. Diesel fuel has a higher energy density than gasoline, contributing to better fuel economy in applications like the Dakar Rally. Performance metrics like torque are high at low RPM, ideal for hauling. Innovations like variable geometry turbocharger and exhaust gas recirculation further optimize efficiency across the engine operating range.

Environmental impact

While efficient, diesel engines emit nitrogen oxide and particulate matter, which are regulated under standards like the Euro 6 in the European Union and Tier 4 in the United States. The Volkswagen emissions scandal highlighted challenges in meeting these regulations. Technologies such as diesel particulate filter and selective catalytic reduction using AdBlue are now mandatory. The International Agency for Research on Cancer classes diesel exhaust as a carcinogen. Future developments focus on compatibility with biodiesel and synthetic fuel, and hybridization in systems like Paris's bus fleet, amid a shift towards electric vehicles in markets such as California.

Category:Internal combustion engine