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Friday, 16 August 2013

Diesel Engines and Gasoline Engines

Diesel engines possess a diversity of features that other internal combustion engines can't match. The advantages of diesel include good thermal efficiency that translates into relatively low CO2 emissions, as well as powerful torque even at low speeds and high durability.
In his 1892 thesis concerning the "Theory and structure of a rational thermal engine that should replace the steam engines and internal combustion engines known today", Rudolf Diesel, the diesel engine's inventor in Germany, described the new engine's basic principles. These are: (1) at first only air is fed into the combustion chamber, then the fuel is sprayed in after the air is compressed; and (2) the air compression ratio is set high so that the air temperature becomes much higher than the combustion point of the fuel.
Diesel engines operate on a self combustion or compression combustion system that does not require ignition plugs and a non-uniform mixing method in which the air and fuel are sent separately into the combustion chamber where they mix together and spontaneous combustion takes place.


Exhaust emission levels are very different between diesel engines and gasoline engines. Diesel engines emit higher levels of nitrogen oxides (NOx) and particulate matter (PM) than gasoline engines.

ItemDieselGasoline
Exhaust emissionsNOx-Better
PM-Better
CO2 (fuel consumption related)Better-
OthersNoise level-Better
Engine torqueBetter-
DurabilityBetter-

Characteristics of Diesel Emissions
Among the substances contained in exhaust emissions, those that have particularly impacts on the environment are carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) and particulate matter (PM). Especially CO2, PM and NOx are attracting serious attention, and a variety of technologies have been developed in order to reduce their generation.

CO2 (Carbon Dioxide)

What is CO2?
CO2 or carbonic acid gas is colorless odorless gas present naturally in the air. The concentration of CO2 is increasing due to the combustion of fossil fuels and the cutting of tropical rainforests. It is important to conserve fossil fuels as much as possible in order to reduce the amount of CO2 generated. Vehicles with good fuel consumption emit lower CO2What happens when the atmospheric CO2 level rises?
Its connection with global warming is most worried. As the average temperature rises, sea levels rise and abnormal climates occur more frequently. The effects of these changes on people around the world are very serious.

PM (Particulate Matter)

What is PM?
PM is a general term for the various kinds of particulate matter emitted by diesel and other engines. This matter consists mainly of soot, half-combusted fuel particles, a lubricated oil component called SOF (Soluble Organic Fraction), and sulfates generated from the sulfur contained in the light oil fuel. PM also includes SPM*, which consist of particularly small particles.
What happens when PM emissions increase?
PM is one of the airborne pollutants that has a direct effect on human health. Breathing in large amounts of PM can result in respiratory problems or chronic lung disease.
* SPM (Suspended Particulate Matter): Among the PM present in engine exhaust gas, those with diameters of less than 10 microns are categorized as SPM. Environmental standards stipulate maximum SPM emission levels.


NOx (Nitrogen Oxides)

What is NOx?
NOx is a general term for a variety of chemical compounds formed in reactions between nitrogen and oxygen at high temperatures. The amount of NOx generated increases as combustion becomes more complete, so to reduce NOx generation the temperature of the reaction must be lowered. This fact makes it difficult to reduce NOx and PM generation simultaneously.
What happens when NOx emissions increase?
NOx is a major cause of photochemical smog and acid rain. It has a huge influence on natural eco-systems by damaging forests and acidifying lakes and marshes. In large cities, high local NOx concentrations may have negative effects on the human respiratory system.
Features of Diesel Engines
Fuel: Diesel light oil
Fuel supply system: High-pressure direct injection into cylinder via fuel pump
Air-fuel mixing: Non-uniform mixing
Ignition system: Compression-induced spontaneous combustion
Compression ratio: 15.5-23
Output control system: Controlled exclusively by fuel injection amount (fixed intake air amount, mixing ratio control)

Combustion
Diesel Engines

In diesel engines, air is drawn into the cylinder and highly compressed, after which fuel is sprayed into the cylinder under high pressure. Ignition occurs spontaneously as a result of the high temperature generated through compression.
Thermal Efficiency
Ratio of heat converted into power against total heat generated during combustion
Diesel Engines Feature High Thermal Efficiency
Thermal Efficiency Ratio=Ratio of heat converted into motive power: 35-42%

CO2Diesel engines' high thermal efficiency translates into low fuel consumption.
20-40% lower than gasoline engines
Durability
Working life of 300,000 - 1,000,000 km or more
(from car-mounted engine data)
PerformanceDiesel engines generate flat torque from the low speed range, so diesel vehicles are easy to drive.
Based on in-house data


Features of Gasoline Engines
Fuel: Gasoline
Fuel supply system: Carburetor or low-pressure intake-pipe fuel injection system
Air-fuel mixing: Pre-injection uniform mixing
Ignition system: Spark ignition
Compression ratio: 8-10.5
Output control system: Suction mixture air amount control via throttle valve (fixed mixing ratio)

Combustion

In gasoline engines, air and fuel are mixed in advance and then drawn into the cylinder and compressed. The compressed mixture is ignited by an ignition plug.
Thermal Efficiency
Ratio of heat converted into power against total heat generated during combustion
Thermal Efficiency Ratio=Ratio of heat converted into motive power: 25-30%

CO2Since gasoline engines have a lower thermal efficiency than diesel engines, their CO2 exhaust amount is correspondingly greater.
DurabilityWorking life of 100,000 - 300,000 km or more
(from car-mounted engine data)
PerformanceGasoline engines generate torque during high-speed rotation.
Source: ISUZU

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