Crude oil is a mixture of various oil products and residues (asphalt). After rectification and purification in the refinery, it is separated from the tower top gas (similar to natural gas), gasoline, kerosene, diesel, and residue (asphalt) in descending order according to the temperature required for distillation equipment production. The product density also increases in sequence. In actual production, most refineries mix half of their kerosene products with gasoline and half with diesel, without producing kerosene products.
Gasoline has a low ignition point and can be ignited by an electric piston. Gasoline engines are small and lightweight, so low-power cars such as small cars, motorcycles, and light tricycles all use gasoline engines. Common gasoline grades include 90 #, 94 #, 98 #, etc., which refer to relative combustion stability. The higher the grade, the better the quality.
Diesel has a high ignition point and needs to be ignited by compressed high-temperature air. The high temperature and pressure determine that diesel engines are relatively bulky, but diesel engines can provide a large amount of power. Therefore, high-power machinery such as ships, cranes, tractors, trucks, and tanks mostly use diesel engines. The common diesel grades are 0 # and -10 #, which refer to the freezing point temperature at which diesel freezes.
The ignition point of kerosene is between the first two, and it can be ignited by an electric piston with stable combustion. In the early days of liberation, most of the lights in rural areas of China were lit with kerosene. And aviation kerosene needs to be specially purified and then modulated, with very high combustion stability. After burning in the aircraft engine, it is quickly sprayed out, providing sufficient power for the aircraft.
1. Gasoline has strong volatility, while diesel is difficult to evaporate, so the pollutants in gasoline vehicles include fuel evaporation emissions, which are composed of hydrocarbons (HC).
2. Gasoline has the characteristic of easy mixing with air and difficult separation after mixing. Gasoline and air can be mixed very evenly, and there is basically no situation of local over concentration or over dilution and liquid oil droplets. The molecules of gasoline are relatively small. The mixture of diesel and air is uneven, inevitably leading to local oxygen deficiency or local oxygen enrichment. Oil is prone to carbonization and the formation of charcoal smoke when exposed to high temperatures and oxygen deficiency. After diesel combustion, some odorous organic gases are generated, so there is still a foul odor in diesel engine emissions.
3. The difference between the two in terms of chemistry: gasoline has fewer carbon atoms, 8-10, while diesel has 12-15, so diesel contains higher energy. Diesel fuel does not need to be ignited and self ignites at high pressures, so its efficiency is relatively high (in fact, the utilization rate is only 30%), but it is very bulky and noisy. Gasoline requires ignition, so gasoline engines are smaller in size and quieter (with a utilization rate of only 15%).
4. The taste is different, gasoline is pungent and diesel has a light taste. The colors are different, gasoline is light in color, diesel is dark in color. Different capacities result in thinner gasoline Diesel fuel is relatively rich. The ignition method is different on transportation vehicles, gasoline is spark plug ignition, and diesel is compression ignition. Diesel has poor anti knock properties. Diesel has lower horsepower, heavier pollution, and emits black smoke compared to gasoline, but its price is lower
Gasoline engines and diesel engines are currently widely used as heat engines in industrial and agricultural production, as well as transportation sectors. Their differences mainly lie in compression ratio, ignition method, fuel used, and purpose.
Compression ratio refers to the ratio of the volume of gas present in the cylinder to the small volume when the piston moves in the cylinder. When the piston is at a certain point, the volume of gas in the cylinder is small. The former is called the total volume of the cylinder, while the latter is called the combustion chamber volume of the cylinder. The compression ratio is defined as compression ratio=total cylinder volume/combustion chamber volume. Compression ratio is an important indicator of internal combustion engines, and the larger the compression ratio, the higher the pressure and temperature. The compression ratio of gasoline engines is 4-6. The compression ratio of a diesel engine is 15-18. In theory, the higher the compression ratio, the higher the efficiency. But because the cylinder is limited by the strength of the material and the temperature of the working fluid inside the cylinder cannot exceed the ignition point of the fuel, the compression ratio cannot be too high.
Their ignition methods are different. Gasoline engines mix gasoline vapor drawn into the cylinder with air, pressurize it, and then ignite it with a spark plug. A diesel engine is a mixture of atomized diesel fuel sprayed from fuel injectors and air, pressurized, and automatically ignited by increasing the temperature of the mixed gas through compression. Gasoline engines use gasoline as fuel, while diesel engines use diesel as fuel. Their names are derived from this.
Gasoline engines are made of materials such as aluminum alloy and plastic. Small size, light weight, easy to start, smooth operation, fast speed, suitable for transportation vehicles such as cars and airplanes that require small size and fast speed. The compression ratio of diesel engines is high, and the cylinders are made sturdy and bulky due to the high pressure they have to withstand. They are generally made of materials such as steel plates and iron plates. It has high power and is suitable for large trucks, tractors, locomotives, and ships with heavy loads.
Gasoline cars and diesel cars have different emission patterns due to the use of different fuels, engine structures, mixture formation methods, and combustion methods. The main differences in emissions between the two are manifested in the following aspects:
1. Gasoline has strong volatility, while diesel is difficult to evaporate, so the pollutants in gasoline vehicles include fuel evaporation emissions, which are composed of hydrocarbons (HC).
2. Gasoline has the characteristic of easy mixing with air and difficult separation after mixing. The formation of fuel mixture in gasoline vehicles is carried out outside the engine combustion chamber (in the carburetor and/or intake pipe), and before ignition, it undergoes intake and compression processes, with a relatively long mixing time. Therefore, gasoline and air can be mixed very evenly, and there is basically no situation of local over concentration or over dilution and liquid oil droplets. The small size of gasoline molecules determines that there are fewer particulate matter in the emissions of gasoline vehicles. The ratio of air to gasoline entering the engine combustion chamber is basically controlled around the theoretical air-fuel ratio (the theoretical air-fuel ratio refers to the amount of air required to burn 1 kilogram of fuel in theory, which is usually around 14.7 for gasoline). Spark plug discharge ignition is used for combustion, and the combustion speed is very fast; Gasoline engines have low compression ratios, low combustion pressures, and high temperatures. The tendency for high-temperature dissociation of combustion products is quite severe, and some "dead zone" points may not ignite or shut off under certain operating conditions, resulting in a higher amount of carbon monoxide (CO) and hydrocarbons (HC) in gasoline engine emissions. At the same time, the high temperature inside the engine combustion chamber leads to the production and emission of nitrogen oxides (NOx). Therefore, the characteristics of gasoline vehicles are high emissions of carbon monoxide (CO) and hydrocarbons (HC), low emissions of particulate matter, and nitrogen oxide (NOx) emissions that are basically the same as diesel vehicles.
3. The formation of fuel mixture in diesel vehicles is carried out in the combustion chamber of the engine. Diesel is high-pressure injected into the combustion chamber, compressed and ignited, and then undergoes diffusion combustion while spraying. This working method determines that the mixture of diesel and air is uneven, inevitably resulting in local oxygen deficiency or local oxygen enrichment. Oil is prone to carbonization and the formation of charcoal smoke when exposed to high temperatures and oxygen deficiency. The adjustment of diesel vehicle load is controlled by changing the fuel injection quantity. The mixture of diesel vehicles is always in a relatively lean state, which means that there is always excess air in the combustion chamber of the diesel engine. These surplus air are prone to produce nitrogen oxides (NOx) under high temperature, while carbon monoxide (CO) and hydrocarbons (HC) are not easily formed. Therefore, the emission characteristics of diesel vehicles are high levels of particulate matter and nitrogen oxides (NOx) emissions, while low levels of carbon monoxide (CO) and hydrocarbons (HC) emissions.
In addition, diesel combustion produces some odorous organic gases, so there is also a foul odor in diesel engine emissions. So gasoline cars can only use gasoline, and diesel cars can only use diesel