Your car’s engine roars to life in milliseconds with every turn of the key or push of a start button. However, for the majority of drivers, what goes on under the bonnet is a black box. It is essential that not only mechanics but drivers should understand the functioning of a car engine so that they can make informed decisions regarding car buying, fuel selection and maintenance. This book explains how the engine works in plain English with practical examples to help you remember.
What is a Car Engine?
A car engine is a device that transforms fuel into movement. It does this by combusting petrol or diesel in an enclosed chamber, generating an explosive force which ultimately causes the car’s wheels to turn. The operation is known as internal combustion and most of the conventional car engines are referred to as Internal Combustion Engines or ICEs.
It’s like a bicycle pump, but in reverse. Air gets hot when it is compressed. When the mixture of fuel and compressed air is ignited, it expands quickly — and the expansion forces a piston to move down hard. Chain this up over several cylinders firing in turn and you have rotational power that powers your car.
Car Engine Types
There are several different types of car engines available, each with its own set of performance requirements and applications.
Inline (Straight) Engine
The cylinders are lined up side by side. Usually found in smaller to medium cars such as the Maruti Swift, Honda City. Economical, space-saving and maintenance friendly.
V-Engine
The cylinders are placed in two rows in the form of a “V”. It’s found in high performance vehicles such as luxury sedans and powerful cars and SUVs like the Toyota Fortuner V6. Provides good power in a compact package.
Flat (Boxer) Engine
Cylinders are lying horizontally on opposite sides. Widely used by Subaru and Porsche. Provides a lower centre of gravity for increased stability and handling.
Rotary (Wankel) Engine
Does not use pistons – uses a rotating triangular rotor. Lighter and quieter, but not as efficient as. Famous in the Mazda RX-7.
Diesel Engine
Runs on compression ignition, rather than spark plugs. Applicable to trucks, buses and SUVs such as the Mahindra Scorpio. Provides high torque, better fuel economy on open road.
Electric Motor
It is not a combustion engine but it is becoming more common in place of the traditional combustion engine. Drives vehicles such as Tata Nexon EV without any direct emissions.
Parts of a Car Engine
It helps if one has an understanding of the major components of the engine before entering the details of how the engine works. All of them serve a particular function and when combined, facilitate combustion.
Cylinders
The cylinders are hollow spaces in which fuel is burned. The number of cylinders in most cars is 4, 6 or 8. A 4-cylinder engine is usually to be found in tiny hatchbacks, such as the Maruti Swift, whereas a V8 is to be found in more powerful SUVs and sports cars. Generally the more cylinders, the more power; however, it also means the more fuel consumption.
Pistons
Each cylinder has pistons which slide up and down within it. As the fuel is combusted, it expands and pushes the piston inwards. Power is generated by this downward movement. Suppose there is a syringe with the plunger as the piston and the tube as the cylinder.Now suppose there is a syringe with the plunger as the piston and the tube as the cylinder.
Crankshaft
The crankshaft turns the up and down movement of the pistons into rotation. This rotation is the one you eventually get to your wheels. Consider the crank on a bike — the pedals move up and down, causing the wheels to rotate in a circular motion. A crankshaft performs the same function as an engine’s pistons.
Camshaft
The camshaft opens and closes the intake and exhaust valves at the proper time. This automates the opening and closing of these valves at the exact right time for each combustion cycle. Variable camshaft timing can extract higher performance in modern type of engines at both low and high speeds.
Valves
There are at least two valves on each cylinder: one for the flow of air-fuel mixture to the cylinder and one for the flow of burned gases from the cylinder. Valves are similar to doors because they open and close in a specific sequence that is timed by the camshaft.
Spark Plugs (Petrol Engines)
Compressed air-fuel mixture is ignited in the cylinder by the spark plugs. The explosion pushes the piston down, and is caused by a small electric spark from the plug. The compression in diesel engines is sufficient to create enough heat to ignite the diesel fuel.In a diesel engine there is no need for a spark plug because compression alone produces enough heat to ignite the diesel fuel.
Fuel Injectors
In modern engines, fuel is directly injected into the cylinder or intake manifold using fuel injectors that provide a precise amount of fuel. It will replace the older carburetors and allow the engine’s computer to precisely control fuel delivery, resulting in better efficiency and less emissions.
The Four Stroke Combustion Cycle Explained
Commonly, most car engines operating today are of the four-stroke cycle type. This is because for each piston movement, there are four movements in total — also known as strokes — to create one power pulse. The knowledge of these 4 strokes is the base on which understanding car engine works.
Stroke 1: Intake
The piston goes down while the intake valve is open. This forms a suction which draws a fuel-air charge into the cylinder. During this time the fuel is sprayed in a fuel-injected engine. Imagine taking a deep breath in — your lungs open to get air. The cylinder is also the same.
Stroke 2: Compression
Both valves are now shut. The piston is now pushed back in the opposite direction, but upwards, so that the air-fuel mixture is squeezed into a much smaller volume. Most petrol engines have a compression ratio of 8:1 to 12:1, which means that the mixture is compressed to 1/8th to 1/12th of its original volume. In the coming explosion, this compression will make it much more powerful.
Stroke 3: Power (Combustion)
The spark plug strikes at the end of the compression stroke. When the fuel-air mixture is ignited, it burns and expands quickly, driving the piston down at a high rate of speed. The only stroke that creates power is this one — the other three strokes are preparation and cleanup. The smoothness comes from the fact that this stroke is repeated four times a revolution of the engine, and the engine has 4 cylinders.
Stroke 4: Exhaust
Again the exhaust valve opens up, and the piston moves up, expelling the used gases (carbon dioxide, water vapor and other products) into the exhaust pipe. This is what is expelled from your car’s exhaust pipe. Once the exhaust stroke is complete, the cycle starts over with a fresh intake stroke.
A useful analogy – to make is that of a bicycle pump: It is pulled back (intake), compressed while held closed (compression), pressed hard (power), and then pushed out (exhaust). The engine does this, but in a continuous, controlled explosion cycle — thousands of times a minute.
How Power goes to the Wheels
When the crank is rotating due to the motion of the pistons, the power flows through a number of parts, ultimately reaching the wheels.
- The crankshaft is meshed with the gearbox (or the transmission), which alters the speed and torque output depending on the gear it is in.
- Manual cars: The driver uses the clutch and gear lever to change gears. This is taken care of automatically by the gearbox in an automatic.
- The gearbox gives power to a driveshaft which is connected to the diff gear and therefore to the wheels.
- When turning corners, the differential lets the left and right wheels spin at different speeds, which is crucial to avoid tyre scrubbing during cornering.
- If, for instance, a Hyundai i20 is being driven around a corner, the outer wheel must cover a greater distance than the inner wheel. This difference is automatically accounted for by the differential, and while cornering won’t feel like something you’re trying to work up to, it will still be safe.
Engine Cooling and Lubrication
When fuel burns in an engine, the temperatures are very high — up to 2,000 degrees of Celsius in the engine cylinder. The engine would seize in minutes if it weren’t for cooling and lubrication.
Cooling System
The cooling system moves a coolant, which is a combination of water and antifreeze, in and out of channels in the engine block. The heat is drawn into the coolant, which is then carried to the radiator by the flow of the coolant, which dissipates the heat by the airflow. Coolant flows to the engine are regulated by a thermostat to maintain the engine at an optimum operating temperature of circa 90°C. The most frequent cause of engine damage is overheating, which can result from a leaky coolant, a faulty thermostat or from another cause.
Lubrication System
Engine oil helps prevent parts of the engine (like camshaft lobes, crankshaft bearings, and pistons) from rubbing against each other. The oil pump forces oil across the narrow passages to all critical areas. Oil degrades over time and deposits contaminants, so it is recommended that oil changes be done at 5,000 to 10,000 km, depending on the type of engine oil and the grade.
Petrol vs. Diesel Engines: Key Differences
Both petrol and diesel engines operate on the four stroke cycle, but they are different because they use different methods to ignite the fuel:
- Spark plugs are used in petrol engines to start a compressed air-fuel mixture. They make more power and pump it out more smoothly, which is why they’re popular on hatchbacks and sedans.
- Diesel engines rely on high compression (14:1 to 25:1) to create heat and consequently ignite diesel fuel. There is no requirement for a spark plug. Trucks, buses and SUVs are frequently utilized for load-carrying and towing due to the higher torque at lower RPMs that diesel engines offer.
The real-life proof: Mahindra’s new diesel Scorpio gets more pulling power on the overland while a petrol Swift is more agile in urban environments thanks to its faster throttle response.
Modern Engine Technologies
Advances in engine technology have come on strong in the last 20 years. Thanks to a series of innovations, engines are more efficient, more powerful and more environmentally friendly:
Turbocharging: A turbocharger forces additional air into the engine where more fuel can be burnt and more power is delivered from a smaller size engine. The Tata Nexon’s 1.0-litre turbocharged engine now generates a power output of more than 120 hp, the same power previously needed by a 1.6-litre engine.
Direct Injection (GDI): Fuel is injected directly into the cylinder at high pressure, resulting in an increase in fuel economy and combustion efficiency, up to 15%.
Variable Valve Timing (VVT): The engine’s valve timing is optimized for various driving conditions, with Variable Valve Timing (VVT) in use to improve power at higher operating speeds and to enhance fuel economy at lower speeds.
Stop-Stop Technology: Reduce fuel consumption by up to 8% in city driving, through engine Auto Start/Stop functionality.
Mild Hybrid and Hybrid Systems: These combine a combustion engine and an electric motor to recover braking energy and boost performance when starting, resulting in a significant improvement in system efficiency.
Frequently Asked Questions
The car battery powers the starter motor which cranks the engine when the start button is pressed or the key is turned in the ignition lock. This puts the pistons into motion. The fuel injectors are pulsing fuel, the spark plugs are firing and the first combustion stroke begins the cycle of continuous combustion. The engine continues to operate on its own combustion cycles once it is running.
Worn piston rings (compression loss), carbon deposits on valves and injectors and weak spark plugs (weak ignition) all reduce the power of engines. Good maintenance (such as replacement of spark plugs, cleaning of the air filter, and fuel system treatment) ensures optimum performance.
CC is cubic centimetres, and takes into account the volume of all the engine’s cylinders added together. A 1,000cc engine (or 1.0L) has an engine displacement of one litre. In general, a higher CC requires greater fuel consumption to produce more power, but consumes more fuel. In comparison to the Toyota Fortuner which has an 800cc engine, a Maruti Alto has a 2,700cc engine.
Old and dirty oil becomes ineffective as a lubricant. Excessive heat and friction create between the metal parts, causing them to wear. In more serious situations, it can lead to “seize up” of the engine, where the pistons and crankshaft jam together. This kind of damage is usually permanent and needs to be fixed with a complete engine rebuild or replacement; an expensive endeavor.
No, they are very different. There is no combustion, no pistons, no valves, no exhaust in electric motors.Electric motors are powered by electromagnetic force, rotates a shaft. Electric motors are simpler, they have less moving parts and require far less maintenance. But they need to store enough battery charge for their range, while combustion engines need to store enough liquid fuel and be able to refuel them quickly.
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