08-16-2017, 11:58 PM
advanced ic engine book vijayaraghavan pdf
OBJECTIVES:
To update the knowledge in engine exhaust emission control and alternate fuels
To enable the students to understand the recent developments in IC Engines
The air-fuel ratio is the proportions by weight of air and gasoline mixed by the carburetor as required for combustion by the engine. This ratio is extremely important for an engine because there are limits to howrich (with more fuel) or how lean (with less fuel) it can be, and still remain fully combustible for efficientfiring. The mixtures with which the engine can operate range from 8:1 to 18.5:1 i.e. from 8 kg of air/kg of fuel to 18.5 kg of air/kg of fuel. Richer or leaner air-fuel ratio limit causes the engine to misfire, or simplyrefuse to run at all.
Stoichiometric Air-Fuel Ratio
The ideal mixture or ratio at which all the fuels blend with all of the oxygen in the air and be completely burned is called the stoichiometric ratio, a chemically perfect combination. In theory, an air fuel ratio of about 14.7:1 i.e. 14.7 kg of air/kg of gasoline produce this ratio, but the exact ratio at which perfectmixture and complete combustion take place depends on the molecular structure of gasoline, which canvary somewhat.
Engine Air-fuel Ratios
An automobile SI engine, as indicated above, works with the air-fuel mixture ranging from 8:1 to 18.5:1.But the ideal ratio would be one that provides both the maximum power and the best economy, while producing the least emissions. But such a ratio does not exist because the fuel requirements of an enginevary widely depending upon temperature, load, and speed conditions. The best fuel economy is obtainedwith a 15:1 to 16:1 ratio, while maximum power output is achieved with a 12.5:1 to 13.5:1 ratio. A richmixture in the order of 11:1 is required for idle heavy load, and high-speed conditions. A lean mixture isrequired for normal cruising and light load conditions. Figure 9.36 represents the characteristic curvesshowing the effect of mixture ratio on efficiency and fuel consumption