Classifications by Number and Arrangement of Cylinders-
|Classification of engines
The automobile engines may have one, two, three, four, six, eight, twelve, and sixteen cylinders. One-cylinder engine is used in scooters and motorcycles. Two cylinder engine is used in tractors. Four, and six-cylinder engines are used in cars, jeeps, buses, and trucks.
American passenger cars have eight-cylinder engines. Twelve- and sixteen-cylinder engines are also used in some passenger cars, buses, trucks, and industrial installations. The three-cylinder engine is used in foreign front-drive automobiles.
The cylinders can be arranged in several ways—vertical, horizontal, in a row (in-line), in two rows or banks set at an angle (V-type), in two rows opposing each other (flat or pancake), or like spokes on a wheel (radial).
Single Cylinder Engine-
Single-cylinder engines are used generally for light vehicles like scooters and motorcycles. The maximum size of the single-cylinder engine is restricted to about 250 — 300 c.c. Jawa has 250 c.c. engine, Rajdoot Motorcycle 175 c.c., Lambretta 150 c.c., Vespa 150 c.c., Vijay Deluxe 150 c.c., Luna, Suvega, and Vicky moped have 50 c.c. engines. Higher engine size
will require heavy engines due to the higher unbalance forces in a single-cylinder engine.
Two Cylinder Engine-
Two-cylinder engines are used mostly in tractors. They are also used in a small German automobile and DAF of Holland cars. The arrangement of the cylinders in the two-cylinder engines may be of three types :
In-line vertical type-
In this type of cylinder arrangement, the two cylinders are placed side by side vertically, so that their cranks are 180° apart. When one cylinder is at T.D.C., the other will be at B.D.C. This type of arrangement provides good balancing and more uniform torque.
In this type of cylinder arrangement, two cylinders are placed with their center lines at some angle to each other. This angle is usually 60 degrees. The engine having this arrangement is more compact and economical. The same crankcase as used in a single-cylinder engine may be used in it.
Opposed type engine-
In this type of cylinder arrangement, the two cylinders are arranged horizontally to each other. The piston and connecting rod movements are identical, which causes the engine to be perfectly balanced, as regards the reciprocating forces. But, because the two cylinders are not in line, the forces in the connecting rods produce a rocking couple. The crankshaft and camshaft are positioned between the two cylinders. The engine having this type of cylinder arrangement can run smoothly at much higher speeds. It also gives much higher outputs. But the length of the engine increases too much and the engine has to be placed in the transverse direction in the car.
The three-cylinder engine is used on a front-drive car, in which the differential is located between the engine and the transmission. The three cylinders are placed in a line. This is a two-stroke cycle engine. The crankcase in this engine serves as an intake and pre-compression chamber. Each cylinder has its own sealed-off section of the crankcase. Thus, the main bearings that support the crankshaft are of the sealed type, so the crankcase is divided into three separate compartments, one for each cylinder.
Four-cylinder engines are mostly used for ordinary cars. The torque obtained is much more uniform as compared to the two-cylinder engine because two working strokes per revolution are obtained. The cylinders of a four-cylinder engine are arranged in the following three types :
In-line verticle type-
In this type of cylinder arrangement, the four cylinders are arranged in one row or line. The first and fourth cylinders are in phase, while the second and third cylinders are also in phase, but in opposite directions. The firing order in the four cylinders is arranged in such a way that at every 180 degrees revolution of the crankshaft, there is one power impulse on it.
In a V4 engine, the four cylinders are in two rows of two cylinders each; and the two rows are set at an angle to each other. The angle of V is kept small, usually, 15° to 20°, because with a larger angle the balancing of the engine becomes more difficult. This type of engine is rather difficult to balance with the counterweights on the crankshaft. It is balanced by using a balance shaft that runs in a direction opposite to the crankshaft. The crankshaft has only two cranks, with connecting rods from opposing cylinders in the two rows being attached to the same crankpin. Each crankpin has two connecting rods attached to it.
Six and Eight Cylinder Engines-
six- and eight-cylinder engines give much smoother torque and higher power. The cylinders of these engines are also arranged in three ways: in-line, V, and opposed type, in the same way as in the four-cylinder engines. In-line 6-cylinder engines and V-8 engines are almost universally in use. The angle between the cylinder rows in V-8 engines is kept usually at 90°. V-8 engines with smaller V-angles have also been made, but the valve operating mechanism is complicated in them.
V-6 engines have two three-cylinder rows that are set at an angle to each other. The crankshaft has only three cranks, with connecting rods from opposing cylinders in the two rows being attached to the same crankpin. Each crankpin has two connecting rods attached to it.
The v-8 engine has two four-cylinder rows that are set at an angle to each other. The crankshaft has four cranks with connecting rods from opposing cylinders in the two rows being attached to a single crankpin. Thus, two rods are attached to each crankpin; and two pistons work to each crankpin. The crankshaft is usually supported on five bearings.
Twelve- and Sixteen Cylinder Engines-
The arrangement of cylinders in twelve- and sixteen-cylinder engines may be of the following types :
1. V-type or pancake-type has two rows of cylinders
2. W-type has three rows of cylinders
3. X-type has four rows of cylinders.
The twelve- and sixteen-cylinder engines have been used in cars, buses, trucks, and industrial installations. The only passenger car now being made with a twelve-cylinder engine is the Ferrari.
Advantages of V-Engines Over In-line Engines-
Although in-line 8-cylinder engines were once widely used in automobiles, they have been superseded by V-8 engines due to having some advantages as follows :
1 V-8 engine permits a shorter, lighter, and more rigid engine. A more rigid engine permits higher running speeds and higher combustion pressure with less difficulty from flexing or bending of the cylinder block and crankshaft. Flexing throws the engine out of line, increases frictional losses and wear; and may also set up internal vibrations.
The shorter engine permits more space for passengers on the small wheelbase. The lighter engine permits the vehicle to be light.
2. It permits the use of an intake manifold that assures relatively even distribution of the air-fuel mixture to all cylinders since all cylinders are relatively close together.
3 It permits the lowering of the hood line and thus a lower car profile. This is because the carburetor and other parts are rested between the two rows of cylinders so they do not take up headroom above the cylinders.