Published on Jan 10, 2016
In developed and developing countries considerable emphasis is being laid on the minimization of pollutants from internal combustion engines. A two-stroke cycle engine produces a considerable amount of pollutants when gasoline is used as a fuel due to short-circuiting.
These pollutants, which include unburnt hydrocarbons and carbon monoxide, which are harmful to beings. There is a strong need to develop a kind of new technology which could minimize pollution from these engines.
Direct fuel injection has been demonstrated to significantly reduce unburned hydrocarbon emissions by timing the injection of fuel in such way as to prevent the escape of unburned fuel from the exhaust port during the scavenging process.
The increased use of petroleum fuels by automobiles has not only caused fuel scarcities, price hikes, higher import bills, and economic imbalance but also causes health hazards due to its toxic emissions. Conventional fuels used in automobiles emit toxic pollutants, which cause asthma, chronic cough, skin degradation, breathlessness, eye and throat problems, and even cancer.
To compare the performance of a carbureted and injected engine at constant speed. Direct injection system was developed which eliminates short circuiting losses completely and injection timing was optimized for the best engine performance and lower emissions.
In a lean burn engine, air fuel ratio is extremely critical. Operation near the lean mixture limit is necessary to obtain the lowest possible emission and the best fuel economy. However, near the lean limit, a slight error in air-fuel ratio can drive the engine to misfire.
A reliable electronic gaseous fuel injection system was designed and built in order to control the engine and also for the evaluation of control strategies. The electronic control unit is used to estimate the pulse width of the signal that would actuate the fuel injector and the start of fuel injection.
The short-circuiting losses of the two-stroke engine can be eliminated by directly injecting the fuel into the cylinder after the closure of the exhaust port. This requires the development of an electronically controlled direct fuel injection system fitted with suitable modification to the engine.
The Figure shows the cylinder wall injection, with an injection nozzle installed in the cylinder wall. The injection nozzle was tilted by 400 from the horizontal and injects the fuel upward, different from the method of injecting the fuel at a right angle to the cylinder axis as employed by Vieillendent, Blair, etc. The spray would be concentrated on the upper position of the combustion chamber near the spark plug.
The location of the nozzle on the cylinder was determined from the pressure crank angle diagram corresponding to an in-cylinder pressure of 2 bar attained after the closure of the exhaust port. Corresponding to this crank angle a hole is drilled in the cylinder bore at an inclination of 400 from horizontal. A water-cooled adaptor was designed for cooling the injector to prevent excess heating of the injector.
Fuel injection timing has a strong influence on the mixing process. In homogeneity in the cylinder charge creates limitations in the optimization of natural gas engines. It has been demonstrated, that poor mixture distribution increases the level of cycle-to-cycle combustion variability.
Mixture formation in a direct injected gasoline fueled engine is largely dependent on the atomization and evaporation of the fuel. While this complexity is not present in gaseous-fueled engines since the mixing process is far from trivial. Due to the lower momentum of injected fuel, the degree of mixing in the region of the jet is lower in the gaseous case than in the liquid case. For this reason, it is important to utilize the timing of the fuel injection event to optimize the mixing process.
Any further increase in the injection advance angle of 2330 results in reduction in maximum brake thermal efficiency is 22.1% at BMEP of 3.45 bar. This is due to the fact that the exhaust gases may carry a small fraction of injected fuel while scavenging.
The maximum brake thermal efficiency of the direct injection engine is 9.1% more than the carbureted engine at 3500 rpm.
There is 79.3% reduction in the unburnt hydrocarbon with electronic fuel injection at 3500 rpm.
The CO emission is 94.5% less in the injected engine compared to the carbureted engine at 3500 rpm.