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Research on Combustion Improvement Techniques by Intake Valve Offset and Squish Effect

Article of Honda R&D Technical Review Vol.25 No.2


Reported in this paper are the technologies for improvement of combustion efficiency by applying two simple methods to a single cylinder, 110 cm3 displacement, four-stroke, two-valve gasoline engine.
In the first attempt, we tried to improve combustion efficiency by increasing tumble of the air-fuel mixture flow. To increase tumble, we devised an offset intake valve design in which a part of the intake valve was located outside of the cylinder bore. With this offset intake valve configuration, a part of the inlet port perimeter was blocked causing disturbance of air-fuel mixture flow along the cylinder wall that resulted in a strong turbulence. The increased turbulence permitted lean burn at an air-fuel ratio leaner by two points, reducing Indicated Specific Fuel Consumption by 4.8% from that of the base engine. With the intake valve shifted outwards against the cylinder bore, the spacing next to the exhaust valve increased, allowing the intake valve diameter to be enlarged to compensate for the deterioration of the maximum power.
In the second attempt, we tried to improve combustion efficiency by increasing the reversed squish flow of the air-fuel mixture. As the means to increase reversed squish flow, we employed a slant-parallel squish configuration. With the application of this squish arrangement, the margin against knocking generation was enhanced and the compression ratio was increased to 9.5 from the original 9.0 while reducing the Indicated Specific Fuel Consumption by 2.6%. The offset intake valve design coupled with the high compression ratio produced by the slant-parallel squish design lowered the Indicated Specific Fuel Consumption by 6.0% compared to the base engine.


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Author (organization or company)

Takamori SHIRASUNA(Motorcycle R&D Center)、Hideki SAITO(Motorcycle R&D Center)、Tomokazu NOMURA(Motorcycle R&D Center)

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