The diesel engine (also known as a compression-ignition engine) is an internal burning engine that uses the heat of compression to begin ignition and burn the fuel that happens to be injected into the combustion chamber. This contrasts with spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which use a spark plug to ignite an air-fuel mixture.

The diesel engine has the greatest thermal efficiency of any standard internal or external combustion engine as a result of its very high compression proportion. Low-speed diesel engines (as used in ships and other applications exactly where general engine weight is relatively unimportant) can have a thermal effectiveness that exceeds 50%.

Diesel machines are manufactured in two-stroke and four-stroke versions. They were originally made use of as an even more efficient replacement for fixed vapor machines. Since the 1910s they have been used in submarines and ships. Use in locomotives, trucks, heavy equipment and electric generating plants followed later. In the 1930s, they slowly began to be used in a few automobiles. Since the 1970s, making use of diesel engines in larger on-road and off-road automobiles in the USA enhanced. According to your British Society of Motor Manufacturing and Traders, the EU average for diesel cars take into account 50% for the complete sold, including 70% in France and 38% in the UK.

Diesel machines have the lowest specific gas consumption of any large internal combustion engine employing a single cycle, 0.26 lb/hp·h (0.16 kg/kWh) for very large marine engines (combined cycle power plants are more efficient, but employ two engines rather than one). Two-stroke diesels with high pressure required induction, particularly turbocharging, make up a large percentage of the very largest diesel engines.

In North America, diesel engines are mostly used in large trucks, where the low-stress, high-efficiency cycle leads to much longer engine life and lower operational costs. These advantages additionally make the diesel engine ideal for use in the heavy-haul railway environment.

Diesel's original motor injected gasoline with the help of compressed air, which atomized the fuel and pushed it into the engine through a nozzle (an identical principle to an aerosol spray). The nozzle opening was shut by a pin valve lifted by the camshaft to start the fuel shot before top dead centre (TDC). This is known as an air-blast injection. Driving the three stage compressor used some power but the efficiency and net power output was more than any other combustion motor at that time.

Diesel engines in service today raise the fuel to extreme pressures by mechanical pumps and deliver it to the combustion chamber by pressure-activated injectors without compressed air. With direct injected diesels, injectors spray fuel through 4 to 12 small orifices in its nozzle. The early air shot diesels constantly had a superior combustion without the sharp enhance in pressure during combustion. Research is today being done and patents are being taken out to again use some form of environment injection to reduce the nitrogen oxides and pollution, reverting to Diesel's original implementation with its superior burning and possibly quieter operation. In all major aspects, the modern diesel engine holds true to Rudolf Diesel's original design, that of igniting fuel by compression at an extremely high pressure within the cylinder. With a great deal higher pressures and high technology injectors, present-day diesel engines utilize the so-called solid injection system applied by Herbert Akroyd Stuart for his hot bulb engine. The indirect injection engine could be considered the latest development of these low rate hot bulb ignition engines.

A vital component of all diesel machines is electronic or mechanical governor which regulates the idling speed and maximum speed of the engine by controlling the rate of fuel delivery. Unlike Otto-cycle motors, incoming air is not throttled and a diesel engine without a governor cannot have a stable idling speed and can easily resulting, overspeed in its destruction. Mechanically governed fuel injection systems are driven by the engine's gear train. These systems use a combination of springs and weights to control fuel delivery relative to both load and speed. Modern electronically managed diesel motors control fuel delivery by use of an electronic control component (ECM) or electronic control unit (ECU). The ECM/ECU receives a motor speed signal, in addition to other operating parameters such as intake manifold pressure and gasoline temperature, from a sensor and controls the amount of fuel and start of injection timing through actuators to increase power and minimise and efficiency emissions. Controlling the timing regarding the begin of injection of fuel into the cylinder is a crucial to minimizing emissions, and maximizing fuel economy (performance), of the engine. The timing is measured in degrees of crank angle of the piston before top dead centre. For instance, if the ECM/ECU initiates gas shot when the piston is 10° before TDC, the start of injection, or time, is said to be 10° BTDC. Ideal timing will depend on the engine design in addition to its speed and load, and is usually 4° BTDC in 1,350-6,000 HP, net, "medium speed" locomotive, stationary and marine diesel engines.

Advancing the beginning of injection (injecting before the piston reaches to its SOI-TDC) results in higher in-cylinder pressure and temperature, and higher effectiveness, but also results in increased engine noise due to faster cylinder pressure rise and increased oxides of nitrogen (NOx) formation due to greater combustion temperatures. Delaying beginning of injection causes incomplete combustion, reduced gasoline efficiency and an increase in exhaust smoke, containing a considerable amount of particulate matter and unburned hydrocarbons.

The term Indirect injection, in an internal combustion engine, refers to fuel shot where fuel is not straight injected into the combustion chamber. Gasoline engines are usually equipped with indirect injection methods, wherein a gas injector delivers the fuel at some time prior to the intake valve.

An indirect injection diesel engine delivers gas into a chamber off the combustion chamber, called a prechamber, where combustion begins and then spreads to the main combustion chamber. The prechamber is carefully designed to guarantee adequate mixing of the atomized fuel with the compression-heated air.

The function of the divided combustion chamber is to speed up the combustion process, in order to increase the power result by increasing engine speed. The addition of a prechamber, however, increases heat loss to the cooling system and thereby lowers engine efficiency. The engine requires glow plugs for starting. In an indirect injection system the air moves quickly, mixing the air and fuel. This simplifies injector design and enables the employment of smaller sized engines much less tightly toleranced designs which are simpler to make and much more reliable. Direct injection, by contrast, makes use of slow-moving environment and fast-moving fuel; both the design and manufacture of the injectors is more difficult. The optimisation of the in-cylinder air flow is much more difficult than developing a prechamber. There is much more integration between the design of the injector and the engine. It is with this reason that car diesel engines had been almost all indirect injection until the prepared availability of powerful CFD simulation systems made the adoption of direct injection practical.

Information technology is made up of a spherical chamber located in the cylinder head and separated from the engine cylinder by a tangential throat. About 50% of the air enters the swirl chamber during the compression stroke of the engine, producing a swirl. After combustion, the products return through the exact same throat towards the primary cylinder at much higher velocity. So more heat loss to walls of the passage takes place. This kind of chamber discovers application in motors in which fuel control and engine stability are more vital than fuel economy. They are Ricardo chambers.

The environment cell is a small cylindrical chamber with a gap in one single conclusion. It's mounted much more or less coaxially with the injector, said axis being parallel to the piston crown, with the injector shooting across a small cavity which is open to the cylinder into the hole in the end of the environment cell. The air cellular is mounted so as to minimise thermal contact with all the mass associated with mind. A pintle injector with a narrow spray pattern is used. At TDC the majority for the charge mass is contained into the cavity and air mobile.

Whenever the injector fires, the jet of fuel enters the air cell and ignites. This results in a jet of flame shooting back out associated with the atmosphere cell directly into the jet of gasoline still issuing from the injector. The turbulence as well as heat give excellent fuel vaporisation and combining properties. Also because the vast majority of the burning takes place outside the air cell in the cavity, which communicates directly using the cylinder, there is less heat loss included in transferring the burning charge to the cylinder.

Air cell injection can be considered as a compromise between indirect and direct injection, gaining some of the efficiency benefits of direct injection while retaining the ease and convenience of development of indirect shot.

Air cell chambers are commonly known as Lanova air chambers.

Smaller diesels can be produced.

The injection pressure required is low, so the injector is cheaper to produce.

The injection direction is of less importance.

Indirect injection is much simpler to design and manufacture; less injector development is needed plus the injection pressures are low (1500 psi/100 bar versus 5000 psi/345 bar and higher for direct injection)

The lower stresses that indirect injection imposes on internal components mean that it is feasible to produce petrol and indirect injection diesel versions regarding the same basic engine. At best such types differ only in the cylinder head and also the demand to fit a supplier and spark plugs in the petrol version whilst fitting an injection pump and injectors to the diesel. Examples range from the BMC A-Series and B-Series engines plus the Land Rover 2.25/2.5-litre 4-cylinder types. Such designs allow petrol and diesel versions of the same vehicle to be built with minimal design changes between them.

Higher engine speeds can be reached, since burning remains in the prechamber.

In cold weather, high speed diesel engines can be difficult to start because the mass of the cylinder block and cylinder head absorb the heat of compression, preventing ignition due to the greater surface-to-volume ratio. Pre-chambered machines make use of small electric heaters inside the pre-chambers called glowplugs, while the direct-injected motors have these glowplugs in the combustion chamber.

Many engines use resistive heaters in the intake manifold to warm the inlet air for starting, or until the engine reaches operating temperature. Engine block heaters (electric resistive heaters in the engine block) connected to the utility grid are used in cold climates when an engine is turned off for extended periods (much more than an hour), to lessen startup engine and time wear. Block heaters are also utilized for emergency energy standby Diesel-powered generators which must rapidly pick up load on a power failure. In the past, a wider variety of cold-start methods were used. Some engines, such as Detroit Diesel engines used a system to introduce small amounts of ether into the inlet manifold to start combustion. Others used a mixed system, with a resistive heater burning methanol. An impromptu method, particularly on out-of-tune engines, is to manually spray an aerosol can of ether-based engine starter liquid to the intake air stream (usually through the intake air filter assembly).

Many diesels are now turbocharged and some are both turbo charged and supercharged. Because diesels don't have fuel in the cylinder before combustion is initiated, more than one bar (100 kPa) of environment can be loaded in the cylinder without preignition. A turbocharged engine can produce significantly more power than a naturally aspirated engine of the same configuration, as having more air in the cylinders allows more fuel to be burned and thus more power to be created. A supercharger is powered mechanically by the engine's crankshaft, while a turbocharger is driven by the engine exhaust, not requiring any mechanical power. Turbocharging can boost the fuel economy of diesel engines by recovering waste heat from the fatigue, increasing the excess air factor, and increasing the ratio of engine output to rubbing losses.

A two-stroke motor does not have a discrete exhaust and intake stroke and hence is incapable of self-aspiration. Therefore all two-stroke engines must be fitted with a blower to charge the cylinders with air and assist in dispersing exhaust gases, a procedure referred to as scavenging. In some cases, the engine may also be fitted with a turbocharger, whose output is directed into the blower inlet.

A few designs employ a crossbreed turbocharger (a turbo-compressor system) for scavenging and charging the cylinders, which device is mechanically driven at cranking and low speeds to act as a blower, but which acts as a real turbocharger at higher loads and speeds. A hybrid turbocharger can revert to compressor mode during instructions for huge increases in motor output power.

As supercharged or turbocharged engines produce even more power for a given engine size as compared to naturally aspirated engines, attention must be paid to the mechanical design of components, lubrication, and cooling to handle the power. Pistons are usually cooled with lubrication oil sprayed on the bottom of the piston. Big motors may make use of water, sea water, or oil supplied through telescoping pipes attached towards the crosshead.

As with petrol engines, you will find two classes of diesel engines in current use: four-stroke and two-stroke. The four-stroke type is the "classic" version, tracing its lineage back to Rudolf Diesel's prototype. It is also the many commonly utilized form, being the preferred power resource for many motor cars, especially trucks and buses. Much larger engines, these types of as used for railroad locomotion and marine propulsion, are often two-stroke units, offering a more favourable power-to-weight ratio, as well as better gas economy. The most effective engines on earth are two-stroke diesels of mammoth dimensions.

Two-stroke diesel engine operation is similar to that of petrol counterparts, except that fuel is not mixed with air before induction, and the crankcase does not take an active role in the period. The traditional two-stroke design relies upon a mechanically driven positive displacement blower to charge the cylinders with air before compression and ignition. The charging process also assists in expelling (scavenging) combustion gases continuing to be from the previous power stroke.

The archetype of the modern form of the two-stroke diesel is the (high-speed) Detroit Diesel Series 71 engine, designed by Charles F. "Boss" Kettering and his co-workers at General Motors Corporation in 1938, in which the blower pressurizes a chamber in the engine block that is often referred to as the "air box". The (very a lot larger medium-speed) Electro-Motive Diesel engine is used as the prime mover in EMD diesel-electric locomotive, marine and stationary applications, and had been created by the same team, and is built to the same principle. However, a considerable improvement built into most later EMD engines is the mechanically-assisted turbo-compressor, which provides charge air using technical assistance during starting (thereby obviating the necessity for Roots-blown scavenging), and provides charge air utilizing an exhaust gas-driven turbine during normal operations—thereby providing true turbocharging and additionally increasing the engine's power output by at least fifty percent.

In a two-stroke diesel engine, as the cylinder's piston approaches the bottom dead centre fatigue ports or valves are opened relieving the majority of the excess pressure and after that a passage between the environment box and the cylinder is opened, permitting air movement into the cylinder. The air flow blows the remaining combustion gases from the cylinder—this is the scavenging process. As the piston passes through bottom centre and starts upward, the passageway is closed and compression commences, culminating in gas injection and ignition. Refer to two-stroke diesel engines for more detailed protection of aspiration types and supercharging of two-stroke diesel engines.

Normally, the number of cylinders are utilized in multiples of two, although any number of cylinders can be used as long as the load on the crankshaft is counterbalanced to prevent excessive vibration. The inline-six-cylinder design is the most prolific in light- to medium-duty motors, though small V8 and larger inline-four displacement engines are additionally common. Small-capacity engines (generally considered to be those below five litres in capacity) are generally four- or six-cylinder kinds, with the four-cylinder being the absolute most common kind found in automotive utilizes. Five-cylinder diesel engines have actually also been produced, being a compromise between the smooth running of the six-cylinder while the space-efficient dimensions of the four-cylinder. Diesel machines for smaller plant machinery, boats, tractors, generators and pumps may be four, three or two-cylinder types, with the single-cylinder diesel engine continuing to be for light stationary work. Direct reversible two-stroke marine diesels need at least three cylinders for reliable restarting forwards and reverse, while four-stroke diesels need at least six cylinders.

The need to enhance the diesel engine's power-to-weight proportion produced several novel cylinder arrangements to extract more power from a provided capacity. The uniflow opposed-piston engine uses two pistons in one cylinder with the combustion cavity in the center and gasoline in- and outlets at the ends. This tends to make a comparatively lightweight, powerful, swiftly running and economic engine suitable for use in aviation. An example is the Junkers Jumo 204/205. The Napier Deltic engine, with three cylinders arranged in a triangular formation, each containing two opposed pistons, your whole engine having three crankshafts, is one of the better known.