Homogeneous charge compression ignition
Homogenous charge compression ignition ( Sheet Homogeneous Charge Compression Ignition, abbreviated as HCCI or Controlled Auto Ignition abbreviated CAI ) is the concept of an engine in which the combustion of a homogeneous mixture in the entire combustion chamber at the same time begins. The primary objective of this development is the reduction of polluting emissions.
The HCCI engine operates with a homogeneous ( uniformly ) distributed mixture of fuel and air. Thereby increasing the ignition temperature and optionally at raised by the compression in the combustion chamber of residual radicals. Unlike the conventional gasoline engine, this auto-ignition is quite desirable and basis of the principle, which is why a spark plug in the HCCI operation is not required. Since HCCI operation is performed only in the partial load range, yet a spark plug is available for engines for gasoline.
Driven with diesel engines operating with the HCCI process, running in the warm-up, idle and full load in conventional diesel mode and under partial load after the HCCI process. However, the HCCI region is diesel fuel more difficult to achieve than with gasoline.
In the HCCI engine, the charge composition will be uniform so that the combustion starts simultaneously in the entire combustion chamber. The regulation of this process can be done by several motor parameters. Is essential to avoid an uncontrolled combustion, because this leads to a knocking combustion with a high pressure gradient. This is acoustically disturbing and can damage the engine. For power control and to reduce the combustion speed, an inner or outer EGR are used. This can be to a certain extent, the combustion position control. Otto engines an inner exhaust-gas recirculation is used to accelerate the ignition of the high octane fuel with free radicals in general. The diesel engine is going the way of the cooled exhaust gas recirculation to slow the chemical reaction, since the temperature lowering of the high ignition quality of diesel fuel counteracts. Due to the almost simultaneous implementation of all of the fuel -air mixture, very high pressure rise rates and peak pressures. For this reason it is not possible for reasons of component strength to drive higher part load points and full load points.
Pollutants such as NOx and soot particles can be inside the engine almost entirely preventable through the homogeneous charge compression ignition. Therefore, one may optionally give up exhaust aftertreatment systems. At the same time, the efficiency is increased. However, the emissions of carbon monoxide and unburned hydrocarbons can not be avoided and are increased.
The compression ratio is always a compromise and the fuel and the selected operating point dependent. The ideal fuel for the HCCI mode is different from the traditional trade fuels. However, it is possible either to use the existing fuel to mix ( fuel diesel ) or additives.
Worldwide research companies and universities the possibility of a homogeneous charge compression ignition engine. The aim is, inter alia, to increase the operating range of the homogeneous charge compression ignition, to improve the power control and the driving comfort and decrease emissions.
Honda used for two-stroke engines Activated Radical Combustion -called homogeneous charge compression ignition process that ignites the mixture without spark ignition in the partial load range. This is achieved by a bleed control, having as an essential element a sensor knock sensor.
As the first HCCI engine applies, apart from the diesel model engines, of Lohmann auxiliary engine of 1949. Here HCCI operation was achieved through a variable compression.