Automobiles/Automotive Engine

I  The vehicle uses for transportation from one place to another place upon the ground or road like cars, trucks & buses and on the air like a plane and in water on the ship, all these things powered by Engine fuel which made by petroleum. (Petrol & Diesel fuel). In the context of Automobiles/Automotive engines, We find Internal Combustion engines (ICE), Four-stroke cycle Engine in your vehicle.

Automobile Engine 

An engine is a machine that converts heat energy into mechanical energy. The heat from combustion (burning ) a fuel produces power which moves the vehicle on the road. Some time engine is also called a power plant.  Automobile engines are Internal Combustion Engine (ICE) because the fuel run them is burned internally or inside the engine. It is powered by either a Petrol engine or Diesel engine. Both engines run with a four-stroke cycle operation. May rotary engine means a rotor that spin or rotates, an engine called a Wankel design in which a three-lobe rotor turns eccentrically in an oval chamber to produce the power it has no engine piston. An example of the rotary engine is the Wankel engine and reciprocating engine mean moving up and down engine piston in the cylinder, they have piston up and down (reciprocates) in the engine cylinder which is most wildly used in heavy-duty vehicle engine and light-duty vehicle engine.

Laterally, two basic piston engines were used on automobile/automotive one is the Spark-Ignition SI Engine. it also called gasoline ( petrol) engine and another is Compression Ignition CI Engine, sometimes it is called a diesel engine, both have four-stroke cycle operational engines. The basic four-stroke events in the engine that take place are Intake Stroke, Compression stroke, Power Stroke and Exhaust stroke.

Working of Conventional automobile engine:

• Intake of the air-fuel mixture 

Air-fuel mixture (air) is sucked into the cylinder, through the air cleaner it reaches the cylinder via intake manifold, intake port and intake valves.

• Compression of the air-fuel mixture (air)

The drawn air-fuel mixture (air) is compressed into the combustion chamber or upper part of the cylinder.

The compressed air-fuel mixture, spark provided by the spark plug with the helps ignition system, thus resulting in the combustion of mixture in the engine cylinder. In gasoline/petrol engine. Similarly, in diesel engines, fuel is injected on the compressed hot air into the combustion chamber using the fuel injection system in a Diesel engine. 

• Power development or conversion of heat energy into mechanical energy

The ignition process starts delivering out heat energy into mechanical energy. The power is transmitted to the crankpin through the connecting rod due to which the crankshaft is rotated. From the crankshaft, the power is transmitted further to drive the vehicle.

• The burnt exhaust gases are expelled out of the engine cylinder.

How does the car engine work?

The spark-ignition (Gasoline / Petrol engine) usually runs on a liquid fuel such as gasoline or petrol. The fuel must be highly volatile so that it vaporiser quickly. the fuel vapour mixes with air before entering the engine cylinder in the Port fuel injection system, Nowaday, Gasoline/Petrol  Direct Injection system fuel mixes with air in the engine cylinder with the swirling process in the cylinder. Then this forms a highly combustible air-fuel mixture that burns easily. The mixture in the cylinder is compressed heat from an electric spark produced by the ignition system set fire to ignite the air-fuel mixture.

As the mixture burns (combustion) high temperature and pressure are produced in the cylinder. This high pressure applied to the top of the piston forces it to move down the cylinder. The motion is carried by gears and shaft to the wheels that drive the car. The wheels turn and the vehicle move. An engine operating on the otto cycle. 

In the diesel or compressed ignition engine, the fuel mixes with air after it enters the engine cylinders. The piston compresses the air to as little as ¹/²² of its original volume. Compressing the air this much raise its temperature to 1000°F (538°C) or higher. A light oil called diesel fuel is then sprayed it injected into the hot air. The hot air heat of compression ignites the fuel. The method of ignition - by the heat of compression gives the diesel engine the compression ignition engine. An engine operating on the diesel cycle, in which the fuel is injected into the cylinder where the heat of compression ignites it that why diesel engine called compression ignition engine. 

Engine Construction

Both diesel and petrol engines are similar in construction, both have a piston that reciprocates (move up and down) in the cylinder. The same action takes place in each cylinder, usually at equally spaced intervals of the crankshaft rotation. Both engines have a cylinder, cylinder head, crankshaft, camshaft and also have piston connecting rod, bearings and valvetrain. Working on the same principle of the four-stroke cycle in both engines. These are intake, Compression, Power and Exhaust. The crankshaft makes two complete revolutions to complete the four-piston stroke. This makes the engine a four-stroke cycle engine. It is also called a four-stroke. The word cycle means a series of events that repeat themselves.

The major difference between petrol and diesel engine are: 

• The type of fuel used. 

• The way the fuel gets into the cylinder.

• The way the fuel ignites the method.

And one of the main differences between petrol and diesel engine, that is a diesel engine usually heavier and stronger. This is because the interval pressure is higher in diesel engines.

Requirements for the operation of an engine:

Fuel: It is the main requirement of the engine. This is needed to provide heat energy to the engine. Petrol and diesel are the main fuel used. Fuel is contained in the fuel tank and is supplied to the engine by a full-fledged fuel injection system.

Air: Air is needed to form a combustible mixture of fuel and air for the engine.In the case of the petrol engine, air and fuel mixture in the cylinder. Air is well cleaned by the air cleaner before it enters the engine cylinder. Air is also required for cooling the engine.

Oil: oil is needed for the engine to act as a lubricating agent to decrease wear and tear engine moving parts. It also helps to decrease noise and cooling agents to eliminate heat generated by the working parts and other several works on it by the lubricant. Oil is supplied to the engine working parts from the oil pan or oil sump with a lubricating system.

Water: In the case of water-cooled engines, water is required for the cooling system. it is filled into the system through the radiator water acts as a cooling agent in the engine.

Spark: In the petrol engine, the spark is required to the provided to the compressed air-fuel mixture for ignition. Spark is provided in the spark plug on the engine by the engine ignition system.

On what bases the automobile/automotive engine can be classified?

Automobile engines can be classified into several ways: 

1. Number of cylinders - (Single & Multi-Cylinder Engine)

2. Arrangements of the cylinder - (Straight (inline), V- type & opposed (flat) type Engine).

3. Arrangements of valve and valvetrain- (Multi-Valve in each cylinder, Over Head Valve (OHV) and Over Head Cam (OHC).

4. Type of Cooling - ( Water and Air Cooling Engine).

5. Number of Stroke per cycle - ( Two or Four).

6. Type of Fuel burned - (Petrol and Diesel Fuel)

7. Method of Ignition - ( Spark-ignition and Compression Heat).

8. Reciprocating or Rotary - (Piston Engine & Wankel Engine)

9. Naturally Aspirated Engine and Turbocharged Engine. 

Four Stroke Petrol Engine Cycle of Operation (Otto Cycle):

INTAKE STROKE

• Piston move downward from Top Dead Centre (TDC).

• Intake Valve is open and exhaust valve is closed.

• Fuel air mixture is the intake (sucked) into the engine cylinder.

COMPRESSION STROKE

• Piston move upward from Bottom Dead Centre.

• Both intake and exhaust valves are closed.

• Drawn in the air-fuel mixture is compressed into the combustion chamber.

• Ignition Process, When the piston reaches near compression top dead centre (TDC) a spark is provided by the spark plug, which ignites the compressed air-fuel mixture.

POWER STROKE

• Rapidly expanding burning gases. Thrust the piston downward from TDC to BDC.

• Both intake and exhaust valves are closed.

• Power impulse is provided to the piston which is transmitted to the crankshaft through the connecting rod.

EXHAUST STROKE

• Piston move upward from BDC. 

• Exhaust valve is open while the intake valve is closed. 

• Burnt gases are expelled out of the engine cylinder. 

Another intake, compression, power and exhaust stroke repeats. These go on continuously in all engine cylinders as long as the engine runs. 

Four Stroke Diesel Engine Cycle of Operation (Diesel Cycle):

INTAKE STROKE

• Air from the atmosphere is intake (sucked) into the cylinder through the air cleaner. 

• The piston downward movement of the from TDC to BDC. 

• Intake valve is open and the exhaust valve is closed.

COMPRESSION STROKE

• Piston moves upward from BDC to TDC. 

• Both intake and exhaust valves are closed.

• The drawn air is compressed into the combustion chamber.

• Injection Process, When the piston reaches near compression Top Dead Centre (TDC). Fuel is an injection into the combustion chamber using the fuel injection system.

POWER STROKE

• As soon as the injected fuel comes in contact with compressed hot air, it catches fire. The gases expand rapidly and provide power impulse to the piston.

• Piston moves downward from TDC to BDC carrying the power produced due to the combustion of fuel. 

• Both intake and exhaust valves are closed. 

EXHAUST STROKE

• Piston travels upwards from BDC to TDC.

• Exhaust valve is open and the intake valve is closed.

• Burnt gases are expelled out of the engine cylinder.

In the automobile engine, there is engine classification in a large variety according to the different basis of engine configuration. One of the bases of vehicle engines design is the location of the camshaft means the placement of the camshaft on either cylinder head or cylinder block. The camshaft placed in the cylinder block of this engine is called the Over Head Valve OHV engine or Pushrod engine.  Most of modern engines the camshaft is located on the cylinder head, this engine is called the Over Head Camshaft OHC engine. OHC design engine either one or two camshafts are installed in the cylinder head. 

 Difference between OHV, OHC, SOHC & DOHC design engines

The major difference between OHV, OHC, SOHC and DOHC design engines. The number of camshafts and the location or place of the camshaft in both two-wheeler and four-wheeler vehicles.

OHV - Overhead Valve engine, the camshaft is located inside the cylinder block and valves are operated through lifter, pushrod and rocker arms. OHV Engine has been successfully used for many years even still used on the road. This is a conventional working engine it has longevity and durability, maintenance costs are low too.

OHC - Over Head Camshaft Engines are one or two camshafts installed in the cylinder head, One camshaft with valves is operated either by rrocker'sarms or directly through the hydraulic valve lifters or hydraulic lash adjuster (HLA), this mechanism engine is called Single Over Head Camshaft SO noHC. 

Nowadays modern engines are Duel / Double Over Head Camshaft (DOHC) Engines are which have twin or double camshaft used. This design engine allows better airflow or allows the more air-fuel mixture to enter and burned exhaust gases to escape more freely. This engine is generally a much more efficient engine than the SOHC engine. DOHC Engines' intake and exhaust valves operate separately by each camshaft, These design engines can easily carry out and manage Variable Valve Timing (VVT)  and Variable Valve Lifter (VVL )  for better engine efficiency and power as well as fuel economy plus lower emissions. even four or six camshafts in V- types of engines.