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Working principle of the gasoline engine and diesel engine    2015-12-27   

Energy: a measure of material movement. Corresponding to the material form of various kinds of sports, the energy also has various forms, each other can convert each other, but the total amount. In the thermodynamic energy mainly refers to heat and composed of thermal conversion of mechanical energy. Our car engine, it is the kinds of chemical energy into mechanical energy, fossil fuel, so as to move the car.

Knowledge popularization of gasoline engine and diesel engine working principle of the interpretation

Mentioned above a lot of four-stroke engine, we will be grouped into two categories: the otto cycle characteristics of gas and gasoline engine, diesel cycle characteristic of diesel engine. Modern basic equivalent of gasoline engine, gas engine in cylinder direct injection gasoline engine structure has changed, but is still in the work mechanism of the otto cycle range. In order to facilitate interpretation, hereinafter called gasoline engine and diesel engine.

When it comes to the principle of the engine, many readers will blurt out: four-stroke engine is divided into suction, compression, power, and exhaust four stages. Gasoline engine intake mixture, then compressed first check point, spark plug flame lit mixture, combustion work push the piston to the next check point, then up to discharge waste gas; Diesel engine inhaled pure air, the difference is that in the dead point position will be compressed diesel injection burned in hot air.

But if we ever doubt, why gasoline engine spark plug? Why can't diesel injection gasoline? Why said diesel engine more powerful, more fuel-efficient but comfort is not ideal? Ok, small make up in this article by way of contrast, steam engine and the working principle of diesel engine.

On the surface, two kinds of heat engine in air intake and fuel ignition means you have the difference, while it is burning oil, power, but is at the top of the piston in the combustion appears, happens within a few milliseconds to two machines have different characteristics. This is the small make up often mention the otto cycle and diesel cycle of difference.

Knowledge popularization of gasoline engine and diesel engine works reading literacy gasoline engine and diesel engine working principle of the interpretation

Two kinds of cycle working status and the corresponding p - v figure Otto cycle is seen on the left, the right for the diesel cycle

Two kinds of processes of the cycle

We say first on the left side of the otto cycle. As shown in the above, the p in cylinder pressure, v content product on behalf of the cylinder, A - B suction stroke, the piston downward to breathe in, when gas pressure is almost unchanged; B - C adiabatic compression stroke, the piston upward compression, the increase of gas pressure, the piston on gas power, the mechanical energy consumption, increase the internal energy of the gas (temperature); C-d constant volume combustion process of gas combustion suddenly, the pressure surge, in this moment also can not afford time to change volume, so it can be regarded as constant volume change, D - E adiabatic power stroke, the gas pressure increase the adiabatic expansion drive piston downward after work, consumption of internal energy into mechanical work itself at the same time, the pressure decreases; E - B isochoric exhaust process, work is done by the end of the stroke, the exhaust valve open, suddenly reduce the gas pressure and the volume is too late to change; B - A exhaust stroke, the piston due to inertia effect to continue upward movement, eliminate waste at the same time, when the pressure stays the same.

As a constant pressure burning diesel cycle, C - D - E for the power stroke. Phase 1 C - D for pressure combustion process, such as burning diesel, the piston moving in a certain pressure constant pressure and volume increase, forces the pistons to work while burning fuel, D, E for adiabatic power stroke. The same goes for other phases. P - v curves in the figure, of course, is an ideal situation, and have certain differences in actual working condition, as a high speed passenger car between two cycle of diesel engine, the combustion process in two stages, the first half as the constant volume combustion, second half as the isobaric combustion, satisfy the high speed also follow the classic characteristics of diesel engine.

Do you know? Diesel is easier than gasoline ignition

Gasoline engine and diesel engine long-term coexistence of reason, is because of the presence of gasoline and diesel fuel, thus there are two kinds of various fuels can give full play to the characteristics of internal combustion engine. This seemingly useless talk, but also verified that sentence 'existence is reasonable.

Gasoline and diesel, are made by composition of carbon and hydrogen of two elements of hydrocarbon compounds. Gasoline is made up of 5 to 9 carbon molecule hydrocarbon, and hydrocarbon composition of diesel on the number of carbon atoms has 10-20, due to the gas molecules are smaller than diesel, so better gasoline volatile, burning speed is faster, but long chain structure of diesel more easily by oxidation, so diesel combustion is lower than gasoline.

Diesel more easily than gasoline ignition? Seems very hard to understand, but it's the truth. We compared the hydrocarbon to common wood, gasoline is just like a pile of wood shavings, can be blow fell slowly in the air, while diesel is like toothpicks, how to throw up will do free fall; Wood with a match it is difficult to ignite, but toothpicks can easily be lit; But throw the wood in the fire, into a fire in an instant, and toothpick at least can burn a few seconds.

Knowledge popularization of gasoline engine and diesel engine works reading literacy gasoline engine and diesel engine working principle of the interpretation

Two kinds of the difference between the engine is not a simple compression and light, this is just the beginning

It is because of these differences, also has the difference between two kinds of engine and features

Faster than diesel volatilization, gasoline, so the gas can state in the suction stroke mixture into the cylinder, and diesel less volatile, not easy to form mixture, so only before the start of the power stroke directly sprayed into the cylinder.

Spontaneous combustion point lower than gasoline, diesel, diesel can be so spontaneous combustion in high temperature and high pressure cylinder; And if the pressure of engine combustion mode, there must be a higher pressure, resulting in a higher temperature to ignite, but because of the gasoline volatile, volatile and will absorb a lot of heat, this is again increased the difficulty of the compression, so a spark plug ignites is the most suitable way.

Faster than diesel, gasoline, so the gas under high temperature and high pressure environment is too strong, the body can't bear the gunpowder temper, so to reduce the pressure of the cylinder, and a spark ignited, the flame in the cylinder is spread in the form of 'waves' burning, this would be to avoid the impact of the detonation formation; And diesel fuel in high temperature and high pressure air, several flame formed at the same time, also is in the form of deflagration (' knock 'similar and gasoline engine) to do work, work status is rough, but because diesel combustion slower, so although the beginning of a very severe burning, burning time is longer than the gasoline engine.

Digression: this is not the gas accelerator

Gasoline engine by the accelerator pedal changing throttle opening, control the number of the mixture into the cylinder, in order to achieve different power output; And diesel engine power output control depend entirely on the amount of fuel injection, is the true sense of the accelerator, cancelled the throttle, the engine intake is more plentiful, burning more fully, this is also one of the reasons for the diesel engine thermal efficiency is higher.

Knowledge popularization of gasoline engine and diesel engine works reading literacy gasoline engine and diesel engine working principle of the interpretation

With 2011 touareg, on the left side of the engine up to 6000 RPM, basic cannot be reached

And the right side of the gasoline engine, 6000 RPM is only red line start

Gasoline engine and diesel engine analysis

After mixture gas ignited in gasoline engine, the instant combustion, and a burst of energy, so you can in a unit time can repeat the cycle, with high speed and output power, small volume, light weight, can have a high performance and faster response speed, wide speed range can also lead to better control. But gasoline engine compression ratio, often only half of the diesel engine, the power stroke than temperature and pressure in cylinder diesel engine is much lower, so the thermal efficiency is lower, which is commonly known as the "oil".

Diesel engine fuel injection, combustion will take time, so is suitable for low speed fuel burn adequately to bring large torque, and in order to fight against high pressure and large torque in the cylinder, the cylinder and the piston connecting rod of diesel engine and other parts should be stronger than gasoline engines, so more bulky than gasoline engines. But it is also because of high compression ratio characteristics of low speed diesel engine, can bring a better heat into kinetic energy, so have better thermal efficiency of diesel engine, which is better fuel consumption performance. This is usually use gasoline engine cars and car racing, and large vehicles such as buses, trucks use diesel engine.

Knowledge popularization of gasoline engine and diesel engine working principle of the interpretation

In order to adapt to the working condition of diesel engine, the current domestic passenger car diesel engine cylinder block is also the heavy cast iron manufacturing

Diesel engine status quo

With the development of technology, the diesel engine on the ride comfort and volume have very big improvement, manufacturing process of high strength aluminum alloy cylinder block, reduce the weight of the engine. Particle recycling exhaust aftertreatment and effectively reduce the exhaust pollution; High pressure common rail fuel injection and low compression ratio (compared with the traditional diesel engine) suppress noise effectively; The application of balance shaft enhanced comfort; Variable cross-section VGT turbine and inter-cooled device improves the engine power, many excellent design gradually equipment on passenger cars (click to enter: strong efficient environmental protection Passenger car diesel engine technology) is analysed, let a capital can compete with gasoline engine, diesel engine and its lower carbon emissions and excellent torque at low speed, accepted by many SUV and even cars.

In Europe, the proportion of diesel vehicles in passenger car has reached 40%, and domestic diesel engine main collocation of the SUV models, most recently, the domestic independent brand diesel cars have also been listed. But at present domestic diesel quality is not good enough, causing diesel engine in China is not seriously. Main problem is the low cetane number (bad combustibility), high sulfur content (damage) engine components increase exhaust pollution, too much polycyclic aromatic hydrocarbons (namely impurities, too much bad combustion will be coked carbon), etc., if China's diesel quality can improve, believe in front of soaring oil prices and the deteriorating environment, people will gradually accept the diesel.