What is a cylinder?  Meaning of symbols i4, V6, V12, W12 in car engines

What is a cylinder? Meaning of symbols i4, V6, V12, W12 in car engines


In car specifications, you will often see the symbols I4, V6… or the terms 4-cylinder, 6-cylinder… So what is it?

What is an automobile cylinder?

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Cylinders are an important part of an automobile engine. This is where the combustion of the gas and fuel mixture takes place so that the piston moves, causing the crankshaft to rotate, thereby helping the engine generate work.

The cylinder is where the combustion of the gas and fuel mixture takes place to move the piston
The cylinder is where the combustion of the gas and fuel mixture takes place to move the piston

Some concepts and knowledge related to automobile cylinders:

Cylinder working space (combustion chamber): Limited by piston top, cylinder cover and cylinder wall. Accordingly, the cylinder working space volume will change with the movement of the piston up or down, at top or bottom dead center.

Cylinder capacity: Is the volume of the cylinder working space limited by 2 perpendicular planes from the center of the cylinder, passing through the top and bottom dead centers.

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Number and arrangement of cylinders in the engine


The engine may consist of one or more cylinders. The number of cylinders in a car engine is usually 3, 4, 5, 6, 8, 12… In which the most common are 4-cylinder and 6-cylinder engines. There are many types of cylinder arrangements inside automobile engines. The most common type is I-cylinder in line, V-type – cylinder in opposite position, W-type, etc. The larger the number of cylinders, the more complicated arrangement will be to ensure the size and consistency. Engine performance is optimized.

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Automotive engine I4 - 4 cylinders in line
Car engine I4 – 4 cylinders in line

In the model’s specifications, the manufacturers clearly mention the number of cylinders and the arrangement in the form of symbols including the type of cylinder arrangement along with the number of cylinders.

For example:

  • I4 engine: The engine has 4 cylinders arranged in a straight line like the letter I (1 row of 4 cylinders)
  • V6 engine: The engine has 6 cylinders arranged in a V-like pattern (2 rows, 3 cylinders in each row)
  • V8 engine: The engine has 8 cylinders arranged in a V-like pattern (2 rows, 4 cylinders in each row)
  • W12 engine: Engine with 12 cylinders arranged in the letter W (4 rows – 3 cylinders each row)
  • W16 engine: Engine with 16 cylinders arranged in the letter W (4 rows – 4 cylinders each row)

Current popular cars such as Toyota Vios, Hyundai Accent, Mazda 3, Toyota Camry, Toyota Fortuner, Ford Ranger… most of them use I4 – 4 cylinder engines.

Mid-size luxury cars and above such as Audi A6, Lexus LS, Mercedes S-Class, Lexus RX … use V6 engine – 6 cylinders. Large luxury cars such as BMW 750Li, Mercedes Maybach, Mercedes G63, Lexus GX … using V8 cylinders – 8 cylinders.

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V6 engine – 6 cylinders (3 cylinders on each side)
V6 engine – 6 cylinders (3 cylinders on each side)

Super luxury cars or star performance sports cars, super sports cars like the company’s models Aston Martin, Rolls-Royce, Bentley, Lamborghini, Ferrari… usually use V12 or W12 – 12 cylinders.

Why do car engines need so many cylinders?


Crankshaft rotation speed is more even

Car engines need many cylinders to optimize force distribution. For example, a 4-stroke (intake – compression – explosion – exhaust) engine with 1 cylinder needs a crankshaft rotation angle of 720 degrees (equivalent to 2 revolutions) to complete one cycle. That is, 1 combustion cycle will take place after 2 revolutions of the crankshaft. In which, only the explosion period is the work of the loading period, the compression period and the exhaust period causing labor, especially the compression period. So if the engine has 1 cylinder, it will generate work in the form of a circulating pulse.

If traction is to be distributed evenly, the engine needs to take advantage of inertia to keep the rotational speed constant through a heavy flywheel. The heavier the flywheel, the more evenly the force is distributed. However, the heavier the flywheel, the less responsive the engine is.

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The more cylinders a car engine has, the more evenly distributed the crankshaft rotation speed is
The more cylinders a car engine has, the more evenly distributed the crankshaft rotation speed is

Therefore, the engine needs many cylinders. If a 1-cylinder engine, the explosion stroke corresponds to 2 revolutions of the crankshaft, the 2 cylinder engine has only 1 revolution. Similarly, a 3-cylinder engine with a stroke of 720 degrees / 3 is 240 degrees of rotation. 4-cylinder engine is 720 degrees / 4 is 180 degrees of rotation. With a 12-cylinder engine, the explosion only needs 720 degrees / 12 is 60 degrees of rotation. It is possible that the more cylinders the engine has, the more uniform the power output will be.

Better balance

Using multiple cylinders instead of just one will help reduce the weight of each piston significantly. This makes the inertia smaller, the engine has better balance. Since then the speed of the engine is also faster due to the lighter weight of each piston.

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Reduce intake/exhaust pipe resistance

The more cylinders an engine has, the more intake/exhaust pipes it will have. This helps reduce drag on the pipeline, supports the intake / exhaust process better, the engine achieves higher power.

Depending on the engine capacity, the manufacturer will design the appropriate number of cylinders. For example, a car with 30 – 100 hp usually has 3 cylinders, 100 – 300 hp usually has 4 cylinders, 300 – 400 hp usually has 6 cylinders, 400 – 700 hp usually has 8 cylinders, more 700 hp usually has 12 cylinders.

Van Toan

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