The difference between pistons

The main structure of the pistons of gasoline engines and diesel engines is very different. Generally speaking, the pistons of gasoline engines are smaller in diameter, smaller in wall thickness and lighter in weight. On the other hand, the piston of diesel engine is larger in diameter, thicker in wall thickness and heavier in weight. The piston shapes are quite different.

The biggest difference between a gasoline engine and a diesel engine is the ignition method and air intake: the gasoline engine enters the cylinder with a combustible gas mixed with oil and gas, and the diesel engine is pure air; the gasoline engine is ignited by a spark plug, and the diesel engine is after the compressed air reaches the diesel self-ignition temperature. The hole injects diesel fuel. Due to the high temperature in the cylinder at this time, the diesel fuel spontaneously ignites.

To tell the difference, the most likely is the skirt of the piston, because the piston stroke of most diesel engines is longer than that of gasoline engines, and there may be special shapes on the skirt to match the movement of the flywheel, but not all diesel engines are like this.

First compare the pistons of a 2-valve gasoline engine and a diesel engine: the difference is on the top of the piston. The gasoline engine piston is flat, and the diesel engine piston has a combustion chamber on the top. This is the biggest difference. Then compare the multi-valve gasoline engine piston and the diesel engine piston: both on the top Combustion chamber. But the gasoline engine is relatively simple. The distance between the piston ring grooves of the diesel engine is larger than that of the gasoline engine. The oil ring groove of the diesel engine has holes. The gasoline engine does not. Generally speaking, there is a big difference.

The piston of an automobile engine is one of the main parts in the engine. It forms a piston group with piston rings, piston pins and other parts, and forms a combustion chamber together with the cylinder head, which bears the force of gas and transmits power to the engine through piston pins and connecting rods. Crankshaft to complete the working process of the internal combustion engine. Since the piston is in a harsh working environment of high speed, high pressure and high temperature, and considering the smooth and durable operation of the engine, the piston must also have sufficient strength and rigidity, good thermal conductivity, high heat resistance, and small expansion coefficient. (small changes in size and shape), low relative density (light weight), wear and corrosion resistance, and low cost. Due to the many and high requirements, some of which are contradictory, it is difficult to find a piston material that can fully meet the requirements. The pistons of modern engines are generally made of aluminum alloys, because aluminum alloys have the outstanding advantages of low density and good thermal conductivity, but at the same time they have the disadvantages of relatively large expansion coefficient and relatively poor high temperature strength. These shortcomings can only be achieved through reasonable structural design. to meet usage requirements. Therefore, the quality of the car engine depends not only on the materials used, but also on the rationality of the design.

There are tens of thousands of parts in a car, ranging from crankshafts and gearbox bodies to spring washers, bolts and nuts. Every part has its function, such as the "little bit" like the piston ring, it looks simple in shape, light in weight and cheap in price, but its function is not trivial. Without it, the car will not move, even if it has a little fault, the car will be abnormal, or it will consume a lot of fuel or lack power. In the cooperation of the entire piston group and the cylinder, the piston ring in the piston group is really in contact with the cylinder wall, which fills the gap between the piston and the cylinder wall to close the combustion chamber, so it is also the most easily worn part in the engine. . Piston rings are generally made of cast iron, have a certain elasticity, have various shapes of cross-section, and have a coating on the surface to increase the running-in performance. When the engine is running, the piston will be heated and expand, so the piston ring has an opening gap. In order to maintain the sealing performance during installation, the opening gap of each piston ring should be staggered. A piston often has three to four piston rings, which are divided into two categories: gas rings and oil rings according to their functions. The air ring is installed in the ring groove at the upper end of the piston head to prevent air leakage, transfer the heat of the piston head to the cylinder wall, and evacuate the heat of the piston. The function of the oil ring is to prevent the lubricating oil from entering the combustion chamber and scrape the excess lubricating oil on the cylinder wall back to the oil pan. It is installed in the lower ring groove of the gas ring. As long as the requirements of the sealing function are ensured, the number of piston rings is better than the number. The small number of piston rings not only maintains the minimum friction area, reduces power loss, but also shortens the height of the piston, and accordingly reduces the height of the engine.

If the piston ring is not properly installed or the sealing performance is not good, the oil on the cylinder wall will go up to the combustion chamber and burn with the mixture, causing the phenomenon of oil burning. If the matching gap between the piston ring and the cylinder wall is too small or the piston ring is stuck in the ring groove due to carbon deposits, when the piston reciprocates up and down, it is likely to scratch the cylinder wall, which will cause damage to the cylinder after a long time. Deep grooves are formed on the wall, which is often referred to as the phenomenon of "pulling the cylinder". The cylinder wall has grooves and poor sealing, which will also cause oil burning. Therefore, the working state of the piston should be checked regularly to avoid the occurrence of the above two situations and ensure that the engine is in good operating condition.