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Diesel exhaust is the gaseous exhaust produced by a diesel type of internal combustion engine, regardless of the fuel type or rate of consumption, or speed of engine operation (e.g., idling or at speed), and regardless of whether the engine is in an on-road vehicle, farm vehicle, locomotive, marine vessel, or stationary generator or other application. The physical and chemical conditions that exist inside any such diesel engines under any conditions differ considerably from spark-ignition engines, because, by design, diesel engine power is not controlled by the air/fuel mixture (as in most gasoline engines), but rather it is directly controlled by the fuel supply. For instance, diesel engines generally produce 28 times less carbon monoxide than gasoline engines, as diesels burn their fuel in excess air even at full load. However, the lean-burning nature of diesel engines and the high temperatures and pressures of the combustion process result in significant production of gaseous nitrogen oxides (NOx), an air pollutant that constitutes a unique challenge with regard to their reduction. Total nitrogen oxides from petrol cars have decreased by around 96% through adoption of exhaust catalytic converters as of 2012, while diesel cars still produce nitrogen oxides at a similar level to those bought a decade and a half ago under real world tests; hence, diesel cars emit around 20 times more nitrogen oxides than petrol cars. Modern on-road diesel engines typically use selective non-catalytic reduction (SNCR) systems to meet emissions laws, as other methods such as exhaust gas recirculation (EGR) cannot adequately reduce NOx to meet the newer standards applicable in many jurisdictions. Moreover, the fine particles (fine particulate matter) in diesel exhaust (e.g., soot, sometimes visible as opaque dark-colored smoke) has traditionally been of greater concern, as it presents different health concerns and is rarely produced in significant quantities by spark-ignition engines. Diesel engines produce significant amounts of especially harmful particulate contaminants when running without enough oxygen to fully combust the fuel; when a diesel engine runs at idle, enough oxygen is usually present to burn the fuel completely. As a result of the particulate emissions, exhaust from diesel vehicles has been reported to be significantly more harmful than those from petrol vehicles. Diesel exhausts have been known for their characteristic odors, which changed when the sulfur content of diesel fuel was reduced, and again when catalytic converters were introduced in exhaust systems. Even so, diesel exhausts have always contained an array of inorganic and organic contaminants, varying in degree and concentration depending on fuel composition and engine running conditions. Moreover, diesel exhaust contaminants include substances listed as human carcinogens by the International Agency for Research on Cancer of the U.N.'s World Health Organization. Diesel exhaust pollution is thought to account for around one quarter of the pollution in the air in previous decades, and a high share of sickness caused by automotive pollution. ==Definition and composition== Diesel exhaust is the exhaust produced by a diesel type of internal combustion engine, regardless of the fuel or fuel use, or speed of engine operation (e.g., idling or at speed), and regardless of whether the engine is in an on-road vehicle, farm vehicle, locomotive, marine vessel, or stationary generator or other application. The physical and chemical conditions that exist inside any such diesel engines under any conditions differ considerably from spark-ignition engines; diesel engine power is directly controlled by the fuel supply, not by control of the air/fuel mixture as in conventional gasoline engines. As a result of these differences, diesel engines generally produce a different array of pollutants than spark-driven engines, differences that are sometimes qualitative (what pollutants are there, and what are not), but more often quantitative (how much of particular pollutants or pollutant classes are present in each). For instance, very little carbon monoxide is produced, in general, in diesel engines, as they burn their fuel in excess air even at full load. The lean-burning nature of diesel engines and the high temperatures and pressures of the combustion process result in significant production of gaseous nitrogen oxide air pollutants. While total nitrogen oxides from petrol cars have decreased by around 96% through adoption of exhaust catalytic converters (as of 2012), while diesel cars still produce nitrogen oxides at a similar level to those bought a decade and a half ago under real world tests; hence, resulting in diesel cars emit around 20 times more nitrogen oxides than petrol cars. Auxiliary diesel systems designed to remediate the nitrogen oxide pollutants are described in a separate section below. More critically, diesel exhaust contains fine particles (fine particulate matter, e.g., soot, sometimes visible as opaque dark-colored smoke), and this is of greater concern as it is rarely produced in significant quantities by spark-ignition engines, and the particulates present significant, distinct health concerns (see below). These especially harmful particulate contaminants are at their peak when such engines are run without sufficient oxygen to fully combust the fuel; when a diesel engine runs at idle, enough oxygen is usually present to burn the fuel completely. (The oxygen requirement in non-idling engines is usually mitigated using turbocharging.) Diesel exhausts, long known for their characteristic odors, changed significantly with the reduction of sulfur content of diesel fuel, and again when catalytic converters were introduces in exhaust systems. Even so, diesel exhausts continue to contain an array of inorganic and organic pollutants, in various classes, and in varying concentrations (see below). Some components of diesel exhaust are listed as carcinogenic for humans by the IARC (part of the World Health Organization of the United Nations), as present in their List of IARC Group 1 carcinogens. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Diesel exhaust」の詳細全文を読む スポンサード リンク
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