Assignment Help on Effect of Moist Air on Naturally Aspirated Single Cylinder Diesel Engine Performance

INTRODUCTION

The internal combustion engine is a heat engine that converts chemical energy in a fuel into mechanical energy. The power is usually made available on a rotating output shaft. The chemical energy of the fuel is first converted to thermal energy by means of combustion or oxidation with air inside the engine. This thermal energy raises the temperature and pressure of the gases within the engine and the high-pressure gas then expands against the mechanical mechanisms of the engine.

This expansion is converted by the mechanical linkages of the engine to a rotating crankshaft, which is the output of the engine. The crankshaft, in turn, is connected to a transmission or power train to transmit the rotating mechanical energy to the desired final use.

The internal combustion engines which were invented in the last decades of the 19th century began to influence on human activities and environment in the beginning of the 20th century. At the end of the century the air pollution with combustion products and immoderate consumption of energy resources became unbearable 

The diesel engine (also known as a compression-ignition engine) is an internal combustion engine in which ignition of the fuel that has been injected into the combustion chamber is initiated by the high temperature which a gas achieves when greatly compressed (adiabatic compression). This contrasts with spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which use a spark plug to ignite an air-fuel mixture.

The diesel engine has the highest thermal efficiency of any standard internal or external combustion engine due to its very high compression ratio and inherent lean burn which enables heat dissipation by the excess air. A small efficiency loss is also avoided compared to two-stroke non-direct-injection gasoline engines since unburnt fuel is not present at valve overlap and therefore no fuel goes directly from the intake to the exhaust. Low-speed diesel engines (as used in ships and other applications where overall engine weight is relatively unimportant) can have a thermal efficiency that exceeds 50%.

Diesel engines are manufactured in two-stroke and four-stroke versions. They were originally used as a more efficient replacement for stationary steam engines. Since the 1910s they have been used in submarines and ships use in locomotives, trucks, heavy equipment and electricity generation plants followed later. In the 1930s, they slowly began to be used in a few automobiles. Since the 1970s, the use of diesel engines in larger on road and off-road vehicles in the USA increased. According to the British Society of Motor Manufacturing and Traders, the EU average for diesel cars account for 50% of the total sold, including 70% in France and 38% in the UK.The world's largest diesel engine which produces a peak power output of 84.42 MW (113,210 hp) at 102 rpm.

A petrol engine (known as a gasoline engine in North America) is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels. It was invented in 1876 in Germany by German inventor Nikolaus August Otto. The first petrol combustion engine (one cylinder, 121.6 cm3 displacement) was prototyped in 1882 in Italy by Enrico Bernardi. In most petrol engines, the fuel and air are usually pre-mixed before compression (although some modern petrol engines now use cylinder-direct petrol injection).

The pre-mixing was formerly done in a carburetor, but now it is done by electronically controlled fuel injection, except in small engines where the cost/complication of electronics does not justify the added engine efficiency. The process differs from a diesel engine in the method of mixing the fuel and air, and in using spark plugs to initiate the combustion process. In a diesel engine, only air is compressed (and therefore heated), and the fuel is injected into very hot air at the end of the compression stroke, and self-ignites. Because of the difference in burn rates between the two different fuels, petrol engines are mechanically designed with different timing than diesels, so to auto-ignite a petrol engine causes the expansion of gas inside the cylinder to reach its greatest point before the cylinder has reached the "top dead center" (TDC) position.

Spark plugs are typically set statically or at idle at a minimum of 10 degrees or so of crankshaft rotation before the piston reaches TDC, but at much higher values at higher engine speeds to allow time for the fuel-air charge to substantially complete combustion before too much expansion has occurred - gas expansion occurring with the piston moving down in the power stroke.

Higher octane petrol burns slower, therefore it has a lower propensity to auto-ignite and its rate of expansion is lower. Thus, engines designed to run Petrol engines run at higher speeds than diesels, partially due to their lighter pistons, connecting rods and crankshaft (a design efficiency made possible by lower compression ratios) and due to petrol burning more quickly than diesel. Because pistons in petrol engines tend to have much shorter strokes than pistons in diesel engines, typically it takes less time for a piston in a petrol engine to complete its stroke than a piston in a diesel engine. However the lower compression ratios of petrol engines give petrol engines lower efficiency than diesel engines. High-octane fuel exclusively can achieve higher compression ratios.

Lin C. Y. investigated systematically the effects of humidity and temperature of intake air on the performance and emission characteristics of diesel engines in order to improve their design and operations. This study shows that the air consumption rate, brake torque, and nitrogen oxides decrease, while the brake specific fuel consumption, carbon monoxide, and sulfur dioxide increase with both the temperature and humidity of the charge air. 

Talal F. canned out experimentally a performance and emission testing for a single cylinder four-stroke diesel engine to determine the optimum operation conditions for this engine. The studied operation parameters included brake specific fuel consumption (BSFC), the results indicated that the lowest( BSFC) of the engine was found when the engine ran around 1 kW charging load at a speed ranging between 1900 rpm and 2700 rpm.  

Brian D.Feldman Modeling an engine through software methods to obtained reasonably accurate data based on reasonably accurate assumptions. Modeling the 2.5LDetroit Diesel engine will help the Future Truck team to make quick and informed decisions .Assumptions were made in the construction of the model because all operating parameters were not obtainable. However, it can be seen that the model is sufficiently similar to the actual engine because major characteristics such as (BSFC) and exhaust gas temperatures are similar. The most effective strategy for balancing emissions, fuel economy, performance, and cost in a diesel engine requires a combination of techniques.