25-08-2017, 09:32 PM
CATALYTIC LEAN BURN TECHNOLOGY
CATALYTIC LEAN BURN .doc (Size: 599 KB / Downloads: 40)
ABSTRACT:
Emissions due to burning of fossil fuels have a great impact on the environment and global warming. Inevitable increase of the number of automobiles has become more and more a serious problem. Therefore emission and fuel economy regulations are becoming stricter around the world. To cope with these severe regulations on emissions and fuel consumption, great attention is gradually paid to lean combustion engines. Lean Burn Engines (LBE) achieves better fuel economy by improving thermal efficiency and reducing emissions. Since lean burn engines can reduce CO2 by
Combustion, they are evaluated as a useful preventive measure of warming the globe.
In this paper, a 350cc single cylinder 4 strokes Bullet engine is taken as a test engine. The cylinder head is modified to have an additional spark plug and the piston with combustion chamber is coated with catalyst. A modified carburetor was used to supply lean mixture. The results obtained indicate a promising feature of improved performance, more mileage and low emission norms.
INTRODUCTION:
In recent years, development of low emission and low fuel consumption engine becomes more important because of running out of fossil fuels, air pollution and global warming up problems. Various efforts such as methanol, CNG, hydrogen intensified emission and fuel consumption are different facets of same kind of pursuit to conserve energy and reduce pollution. One of the Today’s ultimate requirements is developing engines with lower emission and good fuel economy. This paper throws light over Lean Burn Engines which have lower CO2 emission, good fuel economy, easiness of hydrocarbon after treatment if lean. NOx can be treated by catalyst. SI engines have advantages like high specific output, ease of maintenance etc. They also have certain drawbacks listing are high HC/CO emission, low Brake thermal efficiency. Lean Burn Engines brings us these advantages, with its drawbacks eliminated. Lean Burn Engines have their own problems which could be solved by various effects. An effort to introduce 2 spark plugs along with a catalyst coating in the combustion chamber is made whose results are discussed in this paper.
PRINCIPLE:
A lean burn mode is a way to reduce throttling losses. An engine in a typical vehicle is sized for providing the power desired for acceleration, but must operate well below that point in normal steady-speed operation. Ordinarily, the power is cut by partially closing a throttle. However, the extra work done in pumping air through the throttle reduces efficiency. If the fuel/air ratio is reduced, then lower power can be achieved with the throttle closer to fully open, and the efficiency during normal driving (below the maximum torque capability of the engine) can be higher.
The engines designed for lean burning can employ higher compression ratios and thus provide better performance, efficient fuel use and low exhaust hydrocarbon emissions than those found in conventional petrol engines. Ultra lean mixtures with very high air-fuel ratios can only be achieved by direct injection engines.
The main drawback of lean burning is that a complex catalytic converter system is required to reduce NOx emissions. Lean burn engines do not work well with modern 3-way catalytic converter—which require a pollutant balance at the exhaust port so they can carry out oxidation and reduction reactions—so most modern engines run at or near the stoichiometric point. Alternatively, ultra-lean ratios can reduce NOx emissions.
CONCEPTS OF MULTI POINT SPARK IGNITION:
In a conventional engine supplied with stoichiometric air-fuel ratio the spark ignited by a single spark plug is sufficient to ignite the air-fuel mixture effectively, so that the flame propagates through the mixture burning it completely to reach the cylinder walls.
On the other hand, if the same engine is supplied with an air-fuel mixture leaner than the stoichiometric ratio, the spark produced by a single spark plug fails to ignite the air-fuel mixture effectively, because the flame produced vanishes in the midway of propagation leading to incomplete combustion.
In order to overcome this difficulty, the concept of multipoint spark ignition is introduced where two spark plugs in place of one positioned at an inclination with respect to each other were employed to produce sparks at two different points in the combustion space to facilitate complete combustion of lean mixture.