Introduction of engine working sequence in automobile engine working process

Engine Working Process Four-stroke Gasoline Engine The most common automobile engine is a four-stroke gasoline engine. Four-stroke gasoline engine works circularly through four processes: intake, compression, work and exhaust. The working principle of a four-stroke gasoline engine is shown in the following figure. (1) Intake stroke The intake stroke sucks combustible gas mixed with gasoline and air into the cylinder. After the intake stroke begins, the intake valve opens, the exhaust valve closes, the crankshaft rotates, the piston moves from top dead center to bottom dead center, the volume above the piston increases and the pressure drops. Due to the pressure difference, the combustible mixture of gasoline and air enters the cylinder. (2) Compression stroke Compression stroke increases the pressure and temperature of combustible mixture and creates conditions for rapid combustion. After the compression stroke begins, the intake valve and exhaust valve are closed, the crankshaft continues to rotate, the piston moves from bottom dead center to top dead center, the volume above the piston decreases, the combustible mixture is compressed, and the temperature and pressure rise. At the end of the compression stroke, the pressure is 800~ 1400kPa, and the mixed gas temperature is 350~450. (3) Working stroke The working stroke is to make the compressed combustible mixture burn and expand. During operation, the intake valve and exhaust valve remain closed. When the compression comes to an end, the spark plug produces sparks, and the combustible mixture burns sharply, which makes the pressure and temperature of the combustion gas rise sharply. The piston moves from the top dead center to the bottom dead center and drives the crankshaft to rotate through the connecting rod. (4) Exhaust Stroke The exhaust stroke is to exhaust the exhaust gas after expansion and work in the cylinder. Even if the exhaust stroke starts, the intake valve remains closed, the exhaust valve remains open, and the crankshaft continues to rotate, so that the piston moves from the bottom dead center to the top dead center, and the expanded exhaust gas is pushed out of the cylinder. To sum up, every time the engine completes a cycle, the crankshaft rotates twice (720), the intake valve and exhaust valve open once, and the piston completes four cycles. Among them, the strokes of inhalation, compression and exhaust consume power, and only the strokes of doing work generate power. Working sequence of multi-cylinder engine When a four-stroke engine works, it only works for one cycle, and the other three cycles will consume work. Therefore, because the single-cylinder engine can't work smoothly and can't generate enough power, modern cars adopt multi-cylinder engines, among which four-cylinder and six-cylinder engines are the most common. (1) Working sequence of four-stroke four-cylinder engine The cylinders of four-stroke four-cylinder engine are generally arranged in a line, and the four connecting rod journals on the crankshaft are arranged in a plane, with one and four connecting rod journals on one side and two and three connecting rod journals on the other. When the crankshaft rotates, the pistons of the first and fourth cylinders move up and down simultaneously, and the pistons of the second and third cylinders move up and down simultaneously. So the working sequence of a four-cylinder engine is 1, 2, 4, 3 or 1, 3, 4, 2. (2) Working sequence of four-stroke inline six-cylinder engine The journal of crank connecting rod is mostly arranged as follows. Toward the front of the crankshaft, the first and sixth connecting rod journals are on it, the second and fifth connecting rod journals are inclined to the left, and the third and fourth connecting rod journals are inclined to the right, and the three directions form 120 with each other. Top dead center: the farthest position of the piston crown from the rotation center of the crankshaft, that is, the highest position reached by the piston crown in the figure. Bottom dead center: the position of the piston crown closest to the rotation center of the crankshaft, that is, the lowest position reached by the piston crown in the figure. Piston stroke: the distance the piston moves at top dead center and bottom dead center. Combustion chamber volume: when the piston is at the top dead center, the space volume at the top of the piston. Total cylinder volume: the total space volume at the top of the piston when the piston is at the bottom dead center. Working volume of cylinder: the spatial volume of piston moving from top dead center to bottom dead center. Engine displacement: the sum of the working volumes of each cylinder of a multi-cylinder engine is equal to the product of the working volumes of each cylinder and the number of cylinders. Compression ratio: the ratio of total cylinder volume to combustion chamber volume. Reflects how much gas is compressed in the cylinder.