ENGINE OPERATIONS

 

 INTRODUCTION

The majority of modern cars and light vehicles are powered by four-stroke reciprocating engines with spark ignition. Nicolaus Otto of Germany created the first engine of this kind in 1876. It was given the name Otto-cycle engine as a result. Otto's four stroke engine produced the same amount of horsepower with less weight, ran significantly quicker, and used less cylinder displacement than earlier internal combustion engine designs using the same quantity of fuel. A motorbike and subsequently a horseless carriage were powered by this engine concept a few years later. Other engine types used sparingly in contemporary automobiles are the two-stroke, rotary (Wankel), and compression ignition (diesel) engines.

In a cylinder of an internal combustion engine with spark ignition, a precise combination of fuel and air is compressed. The fuel must be either a combustible gas (like propane or natural gas) or one that quickly vaporises (like gasoline, methanol or ethanol). The combustion of the compressed air-fuel combination drives a cylinder's piston downward. This causes a crankshaft to revolve, which propels the vehicle.

SIMPLE ENGINE

A cylinder, a piston, a connecting rod, and a crankshaft are the components of an easy reciprocating engine. The spherical piston can be compared to a cannonball, and the cylinder to a cannon. A cylinder head seals the cylinder's open end. A connecting rod and a piston pin (also known as a wrist pin) are used to attach the piston to the crankshaft, which is sealed to the cylinder wall by piston rings.

The crankshaft may rotate continuously thanks to this configuration, which enables the piston to return to the top of the cylinder. A large flywheel is fastened to the back of the crankshaft due to the strong impulses on the piston as the gasoline burns in the cylinder. The flywheel's weight combines the power impulses into a single, uninterrupted crankshaft motion.

Each cylinder has a separate combustion chamber in the cylinder head. Air and fuel can enter the cylinder through the intake valve port, and the burnt gases can exit through the exhaust valve port. A poppet-style valve isolates each port from the others. A head gasket secures the head to the cylinder block. The camshaft regulates how wide the valves open.

FOUR STROKE ENGINE OPERATION

The piston moves from TDC (top dead canter) to BDC (bottom dead canter) or from BDC to TDC throughout a stroke. An engine's four-stroke cycle consists of four strokes. The terms "intake stroke," "compression stroke," "power stroke," and "exhaust stroke" are used to describe them.

Intake Stroke 

By performing this motion, a low-pressure space is created, which is then filled by ambient air pressure and fuel through the open intake valve. For every gallon of gasoline, the fuel system supplies, approximately 10,000 gallons of air are pulled in. For combined engine performance, pollution control, and fuel efficiency, the optimal mixture (referred to as stoichiometric) is around 14.7:1 (at sea level).

Older cars used carburettors, whereas more recent cars built from the middle of the 1980s featured fuel injection systems with computer controls. The computer keeps track of how much oxygen is present in the exhaust of the car, and it then modifies the fuel supply to provide the right quantity of fuel and air for each intake stroke.

The intake valve closes, and the piston starts to travel back up in the cylinder as the crankshaft continues to rotate.

Compression Stroke

The air-fuel combination is compressed by the piston as it rises in the cylinder. A petrol puddle that is set ablaze in the open won't generate any electricity. However, if it is contained in a cylinder, useable power can be generated. It is simpler to ignite the combination of air and fuel when it is condensed into a smaller space. 

After the intake stroke is finished, the compression stroke starts at BDC. The mixture is compressed to around 1/8 of its volume when the piston was at BDC as the piston travels towards TDC, and both valves are shut. The compression ratio in this instance is 8:1. The compression ratio is 12:1 if the mixture is compressed to 1/12 of its initial volume.

Power Stroke

The compressed air-fuel combination becomes extremely explosive as the piston nears TDC during the compression stroke. The gasoline ignites when the spark plug in the ignition system produces a spark. Although the air-fuel combination burns, it cannot explode. Because to the mixture's expansion during combustion, the piston must descend down the cylinder until it hits BDC. To propel the vehicle, the piston moves the crankshaft. The expansion stroke is another name for the power stroke.

Gases do escape beyond the rings a little bit during the power stroke. The crankcase becomes under pressure as a result of this blowby leaking.

Exhaust Stroke

The exhaust valve opens, enabling the wasted gases to escape, when the piston approaches BDC during the power stroke. The burning gases are driven through the open exhaust valve because they are still expanding. The piston rises in the cylinder while the crankshaft continues to rotate past BDC, aiding in the expulsion of the residual exhaust gases through the open exhaust valve. The exhaust valve closes just a few degrees after the piston reaches TDC. As the piston descends during the intake stroke, the full four-stroke cycle restarts.

This straightforward explanation does not do the four-stroke cycle justice. The timing of the valves' opening and shutting really defines when each stroke truly starts when the engine is operating.