CVCC
CVCC ( C ompound V ortex C ontrolled C ombustion) is the name of a technology from Honda to reduce emissions of pollutants in car exhaust. CVCC is also a registered trademark of Honda and is a form of stratified charge engine .
trigger
Since 1969, Honda experimented with a stratified charge engine, which should meet the expected strict emissions regulations. In 1972 a corresponding experimental engine was presented to the public. In 1974 such an engine went into series production. CVCC technology enabled Honda to meet stringent US emissions laws for car exhaust without the use of a catalytic converter . CVCC technology was first used in 1975 in the 1.5-liter / 53-hp engine (ED1) of the Civic in the US market.
Namesake
The acronym CVCC gave the Civic series its name.
Layout and function
The main characteristics of the Honda CVCC engine compared to a conventional engine are:
- Modified cylinder head with main combustion chamber and prechamber with an additional small inlet valve that is actuated approximately synchronously with the main inlet valve
- 3-flow carburetor with additional complex load and speed-dependent control
- Exhaust manifold designed as a thermal reactor
- Exhaust preheating of the main combustion chamber mixture
The size of the antechamber is about 10% of the total compression space; it is equipped with a thimble-shaped insert made of high-alloy steel to increase the wall temperature and thus for better mixture preparation.
During the intake stroke, the prechamber is supplied with a rich mixture via the first stage of the carburetor, while the main combustion chamber is supplied with a lean mixture through the second stage, and at higher loads also through the third stage. Since a multiple of the pre-chamber volume is sucked in during the suction process, the fuel-rich mixture flows over into the main combustion chamber. During the compression stroke, this is partially pushed back into the antechamber. Thus, at the time of ignition, three zones of different mixture composition are formed: rich mixture in the antechamber, lean mixture in the main combustion chamber and a mixture cloud of medium composition in the area of the overflow channels. The mixture ignited in the antechamber flows through these overflow channels into the main combustion chamber and ignites the lean mixture there (flare ignition); controlled combustion takes place with an over-stoichiometric air ratio while largely avoiding the peak temperatures of over 1100 ° C, which are decisive for nitrogen oxide formation. The exhaust gases flowing out can react in the downstream exhaust manifold designed as a thermal reactor (lean reactor) and thus mainly further reduce the hydrocarbon emissions (degree of conversion over 90%) but also the carbon monoxide emissions. The reactor itself consists of a voluminous cast iron housing with an internal reactor chamber made of heat-resistant chrome-nickel sheet metal.
At the same time, the intake pipe underneath the carburetor, which is firmly connected to the exhaust manifold, is heated up (hot spot), thus achieving optimal mixture preparation and distribution.
The Honda CVCC engine was the only stratified charge engine of the time that was mass-produced and sold in the USA and Japan. With the tightening of the emission limit values , the limits of such a concept became apparent. In the case of heavier vehicles, it was particularly difficult to reduce nitrogen oxide emissions.
The CVCC engine was later equipped with a catalytic converter, but it disappeared from the market after a relatively short time. In the meantime the regulated three-way catalytic converter had established itself .
Only recently coming stratified used again, but this time as air-compressing direct injection. Examples are the Mitsubishi GDI and VW FSI engines.
literature
Shizuo Yagi, Tasuku Date, Kazuo Inoue; NOx Emission and Fuel Economy of the Honda CVCC Engine ; SAE paper 741158; SAE Stratified Charge Conference 1974, Troy / Michigan (USA)