CVCC, orCompound Vortex Controlled Combustion (Japanese:複合渦流調整燃焼方式,Hepburn:Fukugō Uzuryū Chōsei Nenshō Hōshiki), is aninternal combustion engine technology developed andtrademarked by theHonda Motor Company.^[1]

The technology's name refers to its primary features:Compound refers to the use of two combustion chambers;Vortex refers to the vortex generated in the main combustion chamber, increasing combustion speed, andControlled Combustion refers to combustion occurring in a timely, controlled manner.^[1]

The engine innovatively used a secondary, smaller auxiliary inletvalve to feed a richer air-fuel mixture to thecombustion chamber around the spark plug, while the standard inlet valve fed a leanerair-fuel mixture to the remainder of the chamber, creating a more efficient and completecombustion.^[2]

Following the establishment of an "Air Pollution Research Group" by Honda in 1965, its collection of emissions data fromAmerican automakers, and subsequent research into emissions control andprechambers, the first mention of CVCC technology was bySoichiro Honda on February 12, 1971, at the Federation of Economic Organizations Hall in Otemachi, Chiyoda-ku, Tokyo.^[1]

On the advice ofUniversity of Tokyo professor Tsuyoshi Asanuma, then-HondaR&D Director Tasuku Date, Engine-performance Research Block head Shizuo Yagi, and then-Engineering Design Chief Engineer Kazuo Nakagawa began research intolean combustion. After Date suggested the use of a prechamber, which some diesel engines utilized, the first engine to be installed with the CVCC approach for testing was a single-cylinder, 300 cc version ofHonda's EA engine installed in a modifiedHonda N600 hatchback in January 1970.^[1] This technology allowed Honda's cars to meetJapanese andAmericanemissions standards in the 1970s without the need for acatalytic converter.

A type ofstratified charge technology, it was publicized on October 11, 1972 and licensed toToyota (asTTC-V),Ford,Chrysler, andIsuzu before making its production debut in the 1975ED1 engine. As emission laws advanced and required more stringent admissible levels, CVCC was abandoned in favour ofPGM-FI (Programmed Fuel Injection) on all Honda vehicles. Some Honda vehicles in Japan used electronically controlled "PGM-Carb" carburetors on transitional Honda D, E and ZC engines.

The 1981 amendments to the Clean Air Act made it increasingly difficult for CVCC to meet emissions and Honda joined the wider industry in using 3-way Catalysts.

In 2007, the Honda CVCC technology was added to Japan'sMechanical Engineering Heritage list.

Honda CVCCengines have normal inlet and exhaust valves, plus a small auxiliary inlet valve. On the intake stroke a large amount of a very lean mixture is drawn into the main combustion chamber; at the same time a very small amount of rich mixture is pulled into the pre-chamber near thespark plug. The pre-chamber near the spark plug is contained by a small perforated metal plate. At the end of the compression stroke, the pre-chamber is rich in fuel, there is a moderately rich mixture in the main chamber near the pre-chamber outlet and the rest of the main chamber is quite lean. On ignition, flame fronts emerge from the perforations and ignite the remainder of the air–fuel charge. When the sparkplug in the pre-chamber fires, the rich mixture ignites easily and the flame spreads from there into the main chamber, igniting a mixture so lean it wouldn't have fired satisfactorily with just a sparkplug. The remaining engine cycle is as per a standardfour-stroke engine.

Formation ofcarbon monoxide andhydrocarbons are minimized by the overall leanness of the mixture, and the stable and slow burning in the main combustion chamber keeps peak temperature low enough to suppress formation of oxides of nitrogen while keeping the mean temperature high enough long enough to give low hydrocarbon emissions. The design allowed the engine to burn less fuel more efficiently without the use of anexhaust gas recirculation valve or a catalytic converter, although those methods were installed subsequently to further improve emission reduction.

The most significant advantage with CVCC was that it allowed forcarbureted engines that did not rely on intake swirl. Previousstratified charge engines needed costlyfuel injection systems. Additionally, previous engines tried to increase the velocity and swirl of the intake charge to keep rich and lean mixtures separated; Honda was able to maintain separation via the shape of the combustion chamber.^{[citation needed]}

The design of CVCC also allowed it to be adapted to existing engines, since only the cylinder head needed to be modified.^[1]

Some early CVCC engines had problems with the auxiliary valves' retaining collars vibrating loose. Once unscrewed,oil would leak from thevalvetrain into the prechamber, causing a sudden loss of power and large amounts of smoke to flow from the exhaust pipe. These symptoms usually indicated the failure of critical oil seals in the motor that would result in costly repairs. However, the solution was quite simple; Honda corrected the problem with metal retaining rings that slipped over the valves' retaining collars and prevented them from backing out of their threads.^{[citation needed]}

The 1983Honda Prelude (the first year of the second generation of Preludes) used CVCC in combination with a catalytic converter to reduce emissions, along with two separate side draft carburetors (instead of a single, progressive twin-choke carburetor). This new system was called CVCC-II. The following year, a standard cylinder head design was used, and the center carburetor (providing the rich mixture) was removed. TheHonda City AA, introduced in November 1981, also used a CVCC-II engine called theER.^[3] Its use of CVCC was also known as COMBAX (COMpact Blazing-combustion AXiom).

• Setright, L. J. K. (1975). Some Unusual Engines. London: Mechanical Engineering Publications Limited.
• An Evaluation of a 350 CID Compound Vortex Controlled Combustion (CVCC) Powered Chevrolet Impala

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