Harmful Gases Produced by Automobiles


1. What is emission control system?

The emission control system reduces the emissions, which are harmful to the environment and human beings produced by automobiles.

2. What are emissions?

The term emission gas means the evaporated fuel from the fuel tank and the blow-by gas, which passes between the piston and the cylinder wall, including the exhaust gas. The emission gas is harmful to the environment and human beings because it includes such harmful substances as CO (carbon monoxide), HC (hydrocarbon) and NOx (nitrous oxides). Vehicles equipped with diesel engines emit not only gases such as CO, HC, NOx but also carbon particles, which also affect the environment and human beings.

(1) CO (crbon monoxide)

CO is generated when an insufficient amount of oxygen is taken the combustion chamber (incomplete combustion).

2C (carbon) + O2 (oxygen) 2CO (carbon monoxide)

When CO is inhaled into the human body, it disolves in the blood and the blood’s ability to deliver oxygen is hindered. Breathing in large amounts of CO will result in death.

(2) HC (hydrocarbon)

HC is generated during incomplete combustion in the same way as CO. Also, HC is generated in the following cases

<1>When the temperature of the quenching zone is low, it does not reach the combustion temperature.

<2>The intake gas blows through when the valve timing overlaps. The richer the air-fuel mixture is, the more HC is generated. The leaner it is, the less HC is generated. The generated amounts of HC become greater because it cannot burn when the air-fuel mixture is too lean.

When HC is inhaled into the human body, it becomes cancer-causing agent. It also causes the photochemical smog. Blow-by gas HC :25% Exhaust gas CO :100% HC 55% NOx :100%

(3) NOx (nitrous oxides)

NOx is generated by the nitrogen and oxygen in the air of the air-fuel mixture when the temperature of the combustion chamber rises above about 1,80C (3,272 F). The higher the combustion temperature rises, the more NOx is generated. When the air-fuel mixture is lean, more NOx is generated because the ratio of oxygen in the air-fuel mixture is too high. Therefore, NOx is generated according to the two factors of the combustion temperature and oxygen concentration.

N2 (nitrogen) + O2 (oxygen) 2NO (NO, NO2 or

N2… NOx)

When NOx is inhaled into the human body, it irritates the nose and throat. Also it causes the photochemical smog.

1. Exhaust gas

Exhaust gas is emitted from the exhaust pipe. In theory, only CO2 (carbon dioxide) and H2O (vapor) are generated when burning gasoline. However, all of the gasoline does not react according to the chemical theory due to such factors as air-fuel ratio, N2 (nitrogen) in the atmosphere, combustion temperature, combustion duration, etc. That is how harmful substances such as CO, HC or NOx are generated.

2. Evaporated fuel

Evaporated fuel is emitted into the atmosphere afterthe fuel evaporates from the fuel tank, carburetor, etc. Its main component is HC.

3. Blow-by gas

Blow-by gas blows from the gap between the piston and cylinder wall into the crankcase. It consists of mostly fuel of unburned gas (HC).

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