The power of a car comes from the explosive force generated by the combustion of gasoline or diesel. If gasoline and air are mixed in a sealed container and ignited, an explosion will occur. The car engine is designed based on this principle.
If gasoline and air are mixed in the optimal burning ratio of 1:14.7 and compressed with a strong force to increase temperature, a large explosion will be generated when igniting them. This force is transmitted to the wheels through a series of mechanisms, propelling the car forward.
We often call automobile engines internal combustion engines. Both gasoline engines and diesel engines used in automobiles are internal combustion engines.
How to calculate the displacement and compression ratio of an engine?
Cylinder displacement refers to the volume of gas swept by the piston from the bottom dead point to the top dead point, which depends on the diameter of the cylinder and the stroke of the piston. Engine displacement is the sum of the displacement of each cylinder, usually measured in cc (cubic centimeters), mL (milliliters), or L (liters). Since the cylinder block is a cylinder, its volume is unlikely to be exactly a whole liter, which is why numbers like 1998cc, 2397cc, etc., are used to approximate the displacement of 2.0L, 2.4L, etc.
The larger the displacement of the engine, the more combustible mixture can be inhaled each time, and the stronger the power generated during combustion.
The compression ratio of an engine refers to the ratio of the cylinder volume before compression to the cylinder volume after compression (i.e. the chamber volume).
The piston completes four strokes in the cylinder, including intake, compression, power and exhaust, to complete one working cycle. During this period, the piston moves up and down in the cylinder twice, while the crankshaft rotates twice. If you look at the tachometer on the car, you will know how fast this process is. The numbers on the tachometer reflect the engine speed, but in fact they are the manifestation of the number of explosions in the engine cylinder. The higher the speed, the more explosions occur in the engine, and the greater the output power. For example, if the tachometer pointer points to 6, it means that the engine speed is 6000 rpm per minute, which is 100 rpm per second. Then one piston completes 50 working cycles per second, and the crankshaft rotates 100 times.
The piston moves up and down in the cylinder. The lowest point that the piston reaches is called the lower stop point, and the position where it reaches the top is called the upper stop point. The distance between the upper stop point and the lower stop point is called the stroke. When the piston is at the upper stop point, the space at the top of the piston is called the combustion chamber.
The intake stroke
It refers to when the piston moves downward from the top dead center to the bottom dead center in the cylinder, during which the intake valve opens and the exhaust valve closes. This creates a partial vacuum in the cylinder, which sucks fresh air and gasoline mixture into the cylinder.
Compression stroke
Both the intake and exhaust valves are closed, and the piston moves upward from the bottom dead center to the top dead center, compressing the mixture in the cylinder. The more mixture that enters the cylinder, the closer the piston is to the top dead center position, resulting in higher compression force. During the compression stroke, the maximum pressure of the mixture in the cylinder is called compression force. The purpose of compressing the mixture is to make it mix more evenly, increase its temperature for easier combustion, and generate greater power.
Power stroke
After the intake and exhaust valves are closed, the spark plug jumps out with high voltage spark at the right moment to ignite the mixture, making it burn and produce high pressure to push the piston from the top dead center to the bottom dead center.
Exhaust stroke
When the piston moves from the lower dead point to the upper dead point, the intake valve is closed and the exhaust valve is open. The burned exhaust gas in the cylinder is expelled through the exhaust valve and exhaust pipe as the piston moves upward.
These four processes continue without interruption, and repeat continuously. Therefore, the engine can produce power continuously.
There are two types of automotive engines: reciprocating engines and rotary engines. Currently, most automobiles use reciprocating engines, where the pistons move in a linear reciprocating motion, whether it is gasoline or diesel engines. Rotary engines have pistons that rotate within the cylinder.
The main components of rotary engines have a simple structure, small size, high power, smooth operation at high speeds, and better performance, which has attracted the attention of the automotive industry to carry out research and development experiments. However, after decades of experiments, it has been proven that this engine cannot yet compete with traditional reciprocating piston engines. Its pistons have significant edge wear and high fuel consumption.
The pistons of rotary engines are flat triangular, and the cylinder is a flat box with a piston in the chamber. When the piston rotates in the cylinder as a planetary movement, the volume of the working chamber changes periodically with the rotation of the piston, completing four working strokes: intake, compression, power and exhaust. The piston completes one cycle of the four processes with each rotation. The four processes of the working cycle are the same as the working cycle of reciprocating engines in principle, except for the shape and trajectory of the pistons.
