Brief idea on diesel engine

DIESEL ENGINE

                The diesel engine (also known as a compression-ignition or 'CI' 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 (engine efficiency) of any practical 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/injection 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%.

WORKING

Diesel engines work by internal combustion. First, air is allowed into the cylinder and the piston compresses it—but much more than in a petrol engine. In a petrol engine, the fuel-air mixture is compressed to about a tenth of its original volume. But in a diesel engine, the air is compressed by anything from 14 to 25 times. If you've ever pumped up a bicycle tire, you'll have felt the pump getting hotter in your hands the longer you used it. That's because compressing a gas generates heat. Imagine, then, how much heat is generated by forcing air into 14-25 times less space than it normally takes up. So much heat, as it happens, that the air gets really hot—usually at least 500°C (1000°F) and sometimes very much hotter. Once the air is compressed, a mist of fuel is sprayed into the cylinder typically (in a modern engine) by an electronic fuel-injection system, which works a bit like a sophisticated aerosol can. The air is so hot that the fuel instantly ignites and explodes without any need for a spark plug. This controlled explosion makes the piston push back out of the cylinder, producing the power that drives the vehicle or machine in which the engine is mounted. When the piston goes back into the cylinder, the exhaust gases are pushed out through an exhaust valve and, the process repeats itself.

REASONS FOR MANUFACTURING

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 is currently a Wärtsilä-Sulzer RTA96-C Common Rail marine diesel, which produces a peak power output of 84.42 MW (113,210 hp) at 102 rpm.

 APPLICATION

i. Diesel engines are commonly used as mechanical engines, power generators and in mobile drives.

ii. They find wide spread use in locomotives, construction equipment, automobiles, and countless industrial applications.

iii. Industrial diesel engines and diesel powered generators have construction, marine, mining, hospital, forestry, telecommunications, underground, and agricultural applications, just to name a few.

iv. Power generation for prime or standby backup power is the major application of today's diesel generators.

ADVANTAGES

i. Diesel engines have several advantages over other internal combustion engines:

ii. They burn less fuel than a petrol engine performing the same work, due to the engine's higher temperature of combustion and greater expansion ratio.

iii. The longevity of a diesel engine is generally about twice that of a petrol engine due to the increased strength of parts used.

iv. Diesel fuel has better lubrication properties than petrol as well.

v. Diesel fuel is considered safer than petrol in many applications.

vi. The low vapour pressure of diesel is especially advantageous in marine applications, where the accumulation of explosive fuel-air mixtures is a particular hazard.

vii. For any given partial load the fuel efficiency (mass burned per energy produced) of a diesel engine remains nearly constant.

viii. They generate less waste heat in cooling and exhaust.

ix. Diesel engines can accept super- or turbo-charging pressure without any natural limit, constrained only by the strength of engine components.

x. Biodiesel is an easily synthesized, non-petroleum-based fuel.

DISADVANTAGES

i. Diesel engines are expensive than petrol engines.

ii. Higher maintenance cost.

iii. Higher engines noise.

iv. Higher engine vibration.

v. Diesel engine emits more harmful gases to the environment.

vi. Sluggish acceleration.