Vastinar Antonie GeorgePCMAI-1 Laboratory

March 9th, 2017

Working principles of 4-stroke

and 2-stroke IC engines

Laboratory 1

Laboratory Scheme

• Introduction to ICE (Internal Combustion Engines)• Types of ICEs• 4-stroke and 2-stroke engines• Working schematics of 4-

stroke engine

• Working schematics of 2-stroke engines• References• Discussion

Introduction to ICEReciprocating combustion engines are by far the most common form of engine and prime mover.

Today, internal combustion engines (ICE) are used in automotive, aeronautic and naval fields.

While there are multiple types of ICEs, this laboratory will focus on spark ignition (SI) and compression ignition (CI) engines.

Internal combustion engines work by igniting a pressurized air/fuel mixture and using the kinetic power generated to create rotational movement of a crankshaft.

In order to obtain the necessary power through ignition, the air and fuel first need to be added together, compressed, then exhaust gases need to be evacuated from the chamber.

These steps are achieved via a cyclic motion of the pistons. A cyclic motion ensuring one of the above mentioned steps is called a stroke.

The main goal of every ICE is to generate high work output with increased efficiency.

Types of ICEsGiven their complexity, there are multiple ways to divide internal combustion engines.

The most common ways to divide ICEs are regarding:

• Number of cylinders• Cylinder placement• Ignition type• Number of strokes per cycle

Number of cylinders

Most modern vehicles use an even number of cylinders. Most common configurations feature 3, 4, 6 or 8 cylinders.

The number of cylinders greatly impact the performance of the engine and the emissions generated.

Cylinder placementThere are variations on how cylinders can be included in an engine.

1. In line2. In V-Formation3. Flat (Boxer)

Ignition Type - Spark ignition (SI)

A spark ignition engine uses an electrical spark to ignite the compressed air/fuel mixture

The spark is usually generated by the electrode of a spark plug, synchronized to the piston movement.

Ignition Type – Compression Ignition (CI)

Used mostly on diesel engines, compression ignition makes use of the high air pressure and temperature in the cylinder

When fuel is injected into the compressed air, it self ignites.

Diesel engines also use glow plugs to aid self ignition during cold seasons.

4-stroke ICEAs the crankshaft rotates, the piston creates a reciprocating motion called a stroke.

A crankshaft revolution is equal with two strokes of a piston.

In case of 4-stroke engines, the piston moves 4 times to complete a cycle.

4-stroke ICE - InductionDuring the induction stroke, the piston moves downwards creating a vacuum.

The motion draws a fresh charge through the intake valve, which opens slightly before the piston descents.

4-stroke ICE - CompressionDuring the compression stroke, both intake and exhaust valves are closed.

The piston moves upwards, compressing the air or air/fuel mixture.

4-stroke ICE - IgnitionOnce compressed, the mixture is ignited, either by spark (SI) or through self-ignition (CI).

The force of explosion pushes the piston down, generating the power stroke

4-stroke ICE - ExhaustTo eliminate unburnt gases and combustion residue, the exhaust valve opens.

Shortly after, the piston goes upwards again, pushing the exhaust residue out.

2-stroke ICE

The 2-stroke internal combustion engine uses the same principle to generate kinetic energy from burning fuel.

However, it removes the separate induction and exhaust strokes, thus finishing a cycle with each rotation of the crankshaft.

2-stroke ICE - CompressionThe piston travels up from BDC (bottom dead center), compressing the trapped charge.

If the charge is not pre-mixed, fuel is injected towards the end of the stroke.

Ignition should occur slightly before TDC (top dead center).

During compression, the underside of the piston draws a fresh charge through a non-return valve.

2-stroke ICE - PowerDuring the power stroke, the piston moves downwards, compressing the charge in the crankcase.

Near the end of the stroke, the exhaust port opens, allowing gases to exit the cylinder.

When the piston reaches BDC (bottom dead center), the transfer port opens, allowing the compressed charge into the cylinder.

4-stroke vs 2-stroke

References

V. Ganesan – IC Engines 4th Edition. McGraw Hill Offices• R. Stone – Introduction To Internal Combustion Engines

4th Edition.• Pinterest. Web.• BMW Press. Web.• Engglabs.com. Web.

Questions & Discussion