Due to the high efficiency of the diesel engine is widely used on trucks. However, most cars have diesel engines in engine lineup. In Europe, diesel is gradually replacing gasoline engines, for example, over 50% of new cars have a diesel engine there.
In passenger cars high-speed diesel engines is used, which have a high elasticity, I.e., ability to develop nominal torque over a wide range of engine speed.
How diesel is working
The principle of operation of the diesel engine is based on the spontaneous (compressioned) combustion of diesel fuel injected into the combustion chamber and mix with the compressed air heated to a high temperature. Unlike a gasoline engine, the diesel is not depend on the excess air ratio but defined by heterogeneous (inhomogeneous) of the fuel-air mixture.
The diesel engine has a number of distinctive features:
- It has a large compression ratio and thus a higher efficiency, bigger weight and dimensions, low fuel consumption;
- It has a low speed of the crankshaft and thus lower power density, accompanied by incomplete combustion and therefore soot formation;
- It has no throttle, so the high torque at low engine speeds;
- It has a complex hardware structure of the fuel management system and thus a high sensitivity to the fuel quality.
New features of modern diesel engines
The main directions of improving the diesel engines are reduced fuel consumption, emissions, noise, increased engine power, cold start facilitating. There are a number of systems used to implement these requirements on modern diesel engines: Common Rail, the inlet and outlet systems, exhaust gas recirculation, turbocharger, preheating.
Common Rail injection system involves the accumulation of fuel in the high-pressure injection accumulator and electronically controlled injectors. Electronics provides a well-defined portions of the injection of fuel, thus achieving high savings, complete combustion and increase power. If necessary, the fuel may be injected multiple times during one cycle.
Modern diesel exhaust system aims to reduce soot forming in the exhaust gas, unburned hydrocarbons and nitrogen oxides. To do this the particulate filter is installed. Soot accumulates in the filter and removed by regeneration.
Exhaust gas recirculation is used to reduce the content in the exhaust gas of nitric oxide, for this part of the gas back into the intake manifold. To improve the efficiency of the system the exhaust gases are cooled in a special forced cooler included in the engine cooling system.
The intake system of the diesel engine can be equipped with inlet valves. Application of two flaps channel suction air stream provides turbulence and improved carburetion in all modes. When starting the engine and operating at low speed valve is closed, at high engine speed and high torque – are open. Closure flaps results in a reduction in the exhaust gas of carbon monoxide and unburned hydrocarbons.
The most effective system for increasing the power of the diesel engine is turbocharging. To create the optimum supercharging pressure for all engine operating modes, the system uses a variable geometry turbocharger turbine.
To facilitate the launch of the diesel engine in cold weather, a system plugs warming, which is electronically controlled glow plugs installed in the intake manifold. Additionally, the car may be mounted on the diesel fuel heater.