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.

Item Diesel Gasoline
Exhaust emissions NOx - Better
PM - Better
CO2 (fuel consumption related) Better -
Others Noise level - Better
Engine torque Better -
Durability Better -


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 CO2.

What 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.