If you want to choose the saddest model in the Chinese auto market in 2021, I personally think it is not Nissan's new Qijun. For the replacement of this car, Nissan has spent a lot of money and effort on research and development, equipped with a lot of advanced technology, Nissan has great expectations for this car. But unexpectedly, as soon as the new car was listed, it was smashed by the Chinese media, and sales fell sharply, and finally had to leave the dilapidated Qijun to save the market. The fundamental reason for the defeat of Xinqijun to Maicheng is that it is equipped with a three-cylinder engine. In the minds of Chinese consumers, the three-cylinder engine is "lame", unbalanced and trembling, so it is resolutely not purchased. In particular, this kind of mid-to-high-end car with more than 200,000 cannot accept three-cylinder engines. So, why should New Qijun use this three-cylinder machine that everyone can't see? On this topic, Lao Hou is here to tell you about the knowledge of the number of cylinders in the engine.
The number of cylinders refers to the number of cylinders owned by a single engine. Common automobile engines are single cylinder, double cylinder, three cylinder, four cylinder, five cylinder, six cylinder, eight cylinder, ten cylinder, twelve cylinder, etc., the most is sixteen cylinders. Single-cylinder and two-cylinder engines are generally used in motorcycles, and five-cylinder and ten-cylinder engines are rare in automobiles. Volvo has long used 5-cylinder engines, and Audi now uses 5-cylinder and 10-cylinder engines on some models. There have also been 7-, 9-, and 11-cylinder engines in history, but they are configured as star-shaped, generally used in early aircraft, and rarely used in automobiles.
Throughout the development history of automobiles, the number of cylinders of the engine has experienced the development history of "less- more - less". In the early years, when Carl Benz invented the first car, he used a single-cylinder gasoline engine. Later, with the rapid development of automobile technology, the demand for engine power in automobiles is getting higher and higher, and the number of cylinders of the engine is also increasing, from single cylinder to double cylinder, four cylinder, six cylinder, but with the development of engine technology, the output power gradually rises, and the small displacement engine also has a lot of power. In addition, the oil crisis of the 1970s made people have a rigid demand for reducing the fuel consumption of automobiles, so the number of cylinders and exhaust of the engine have also declined, and there has been a situation in which 4 cylinders are the mainstay, 3 cylinders, and 6 cylinders are supplemented.
Here, first of all, I would like to popularize the knowledge of the cylinder diameter and stroke of the engine. Because the exhaust volume of the engine is the diameter of the cylinder and the product of the stroke, the larger the diameter and stroke of the cylinder, the greater the exhaust volume of the engine. For diesel engines, because the diesel engine is multi-point simultaneous combustion when the cylinder is burning, and it is an isobaric combustion process that burns while injecting, the cylinder diameter of the diesel engine can be very large, and the cylinder diameter of some marine diesel engines is more than 1 meter, but in the case of gasoline engines, the cylinder diameter and stroke cannot be increased indefinitely. Gasoline is ignited by a spark plug in the engine combustion chamber, and the flames spread from the middle to the surroundings. If the cylinder diameter is too large, the combustible mixture at the end automatically catches fire before the flame striker arrives, and the explosion burns, which is harmful to the engine.
Therefore, the cylinder diameter of the gasoline engine cannot be very large. In the early days when the engine compression ratio was not very high, the cylinder diameter could reach up to 110 mm. For example, release the 6102 engine with a cylinder diameter of 102 mm. Dongfeng EQ6100 engine, cylinder diameter 100 mm. In today's gasoline engines, the cylinder diameter rarely exceeds 100mm. For example, the Prado 27 cylinder has a diameter of 95 mm, which is quite large in today's gasoline engines. In this way, the exhaust volume of one cylinder of the gasoline engine is limited to not so large. Now, the displacement per cylinder of many gasoline engines is stable at about 0.5L. It's a balanced choice that balances efficiency and power.
The ratio of cylinder bore to piston stroke is called "bore stroke ratio" and is one of the parameters that measure the direction of engine power. When the bore is greater than the stroke, the engine efficiency decreases, but the speed limit is high, which can produce powerful power at high speeds. Generally used in racing. The cylinder bore of ordinary household engines is smaller than the stroke, so this kind of engine has a tendency to have high thermal efficiency, low speed limit, and higher efficiency; it is said that there are few engines with equal bore, and power and efficiency coexist, but in fact, like the Toyota 86, they are moving towards power. So, let's explain once again why different cylinder counts are chosen with the same exhaust volume. For example, if there is a 3-cylinder and 4-cylinder displacement of the same 1.5L, what is the difference between them?
What we must make clear here is that the smaller the number of engines, the fewer parts, the smaller the friction loss, and the higher the mechanical efficiency of the engine. In addition, the smaller the number of engine cylinders and the larger the cylinder diameter, the smaller the facial ratio of the combustion chamber, the easier the thermal efficiency is improved; in addition, the larger the cylinder bore, the greater the torque of the engine at low speed. Therefore, in an engine with this exhaust volume, the smaller the number of cylinders, the better. For example, the same 2.0L engine, 4 cylinders have better power than 6 cylinders, and fuel consumption is also lower. The 2.0L, 2.5L engines are now barely visible, but they have been replaced by 4-cylinder engines.
On the other hand, the 3-cylinder engine is 1 cylinder less than the 4-cylinder engine, and the camshaft, valve, piston rod, etc. are 1 set less, so the 3-cylinder engine is better than the 4-cylinder engine in terms of thermal efficiency, mechanical efficiency, and dynamics. This is also one of the important reasons for the increasing application of three-cylinder engines in recent years. Objectively speaking, under the same displacement, the three-cylinder engine is indeed superior to the four-cylinder engine, which is in line with the general trend of energy saving and emission reduction and fuel consumption reduction. Everyone's biggest concern about the three-cylinder engine is jitter. In fact, everyone is too worried about this. The current engine technology can well balance the vibration of the engine itself, and can also isolate the vibration of the engine from the body, and the impact of vibration on driving is indeed very small. There are many models equipped with 3-cylinder engines such as BMWx1, Honda Lingpai, Neck, and Volvo XC40, and Toyota Corolla has also replaced the 1.2T cylinder with a 1.5L cylinder this year. In the ordinary family car of the future, the three-cylinder engine is indeed the trend. The tragedy of Xinjun is not in the technology itself, but in the media publicity activities, so it is not much to say in this regard.
Can a small displacement engine have a little more cylinder count? For example, if the 1.5L engine is 6 cylinders, there is no need to worry about the unbalanced fluctuations of the engine. This is certainly possible. For example, the 1.6-liter engine used in the F1 car became a V-6 cylinder. However, this engine is basically a "large diameter, short stroke" design, the engine speed is extremely high, inefficient, huge fuel consumption, and wear is large, the engine life is low, and it is not practical in household cars.