The Operating Principle and Differences Between Two-Stroke and Four-Stroke Engines

When choosing power equipment, it's important to pay special attention to the engine type. There are two types of internal combustion engines: 2-stroke and 4-stroke.

The operating principle of an internal combustion engine is based on the expansion of gases when heated, which is achieved by the forced ignition of a combustible mixture injected into the cylinder's air space.

It's often said that a 4-stroke engine is superior, but to understand why, it's necessary to examine the operating principles of each in more detail.

The main components of an internal combustion engine, regardless of its type, are the crankshaft and valve train, as well as the systems responsible for cooling, fuel supply, ignition, and lubrication.

The transfer of useful work from the expanding gas is accomplished through the crankshaft and valve train, while the valve train ensures the timely injection of the fuel mixture into the cylinder. 

Four-stroke engines are the choice of Honda.

Four-stroke engines are fuel-efficient, quieter, and produce combustible exhaust, making them significantly cleaner than two-stroke engines. This is why Honda uses only four-stroke engines in its power equipment. Honda has been introducing its four-stroke engines to the power equipment market for many years, achieving superior results, and their quality and reliability have never been in doubt. However, let's take a closer look at how two-stroke and four-stroke engines work.

Two-Stroke Engine Operation

The working cycle of a two-stroke engine consists of two stages: compression and power stroke.

Compression. The primary piston positions are top dead center (TDC) and bottom dead center (BDC). As the piston moves from BDC to TDC, i

t

 alternately closes first the scavenge port and then the exhaust port, after which the gas in the cylinder begins to compress. At the same time, a fresh combustibl

e mixture enters the crankcase through the intake port, which will be used for subsequent compression.

Power stroke. After the combustible mixture has been compressed to its maximum, it is ignited by an electric spark generated by a spark plu

g. The temperature of the gas mixture rises sharply, and the volume of the gas rapidly increases, creating pressure that forces the piston to move toward BDC. A

s the piston descends, it opens the exhaust port, expelling the combustion products of the combustible mixture into the atmosphere. Further movement of th

e piston leads to compression of the fresh combustible mixture and opening of the purge hole, through which the combustible mixture enters the combustion chamber.

The main drawback of a two-stroke engine is its high fuel consumption, some of which is lost to useful use. This is due to the moment when the purge and exhaust ports are simultaneously open, resulting in partial release of the combustible mixture into the atmosphere. There's also constant oil consumption, as two-stroke engines run on a mixture of gasoline and oil. Another inconvenience is the need to constantly prepare the fuel mixture. The main advantages of a two-stroke engine remain its smaller size and weight compared to its four-stroke counterpart, but the size of the power equipment allows for the use of four-stroke engines, which is significantly less troublesome during operation. Therefore, two-stroke engines are largely reserved for various modeling applications, particularly aircraft modeling, where even an extra 100 grams can make a difference.

The operating principle of a four-stroke engine

 

A four-stroke engine operates significantly differently from a two-stroke engine. The four-stroke engine's operating cycle consists of four stages: in

 

take, compression, power stroke, and exhaust, made possible by the use of a valve system.

During the intake stage, the piston moves downward, the intake valve opens, and the combustible mixture enters the cylinder chamber. When mixed with the remaining exhaust mixture, it forms the working mixture.

During compression, the piston moves from BDC to TDC, with both valves closed. The higher the piston rises, the higher the pressure and temperat

ure of the working mixture.

The power stroke of a four-stroke engine is the forced movement of the piston from TDC to BDC due to the action of the rapidly expanding working mixture, ignited by the spark plug. Once the piston reaches BDC, the exhaust valve opens.

During the exhaust stage, the combustion products displaced by the piston moving from BDC to TDC are expelled into the atmosphere through the exhaust valve.

Thanks to the use of a valve system, four-stroke internal combustion engines are more fuel-efficient and environmentally friendly, eliminating the emission of unused fuel mixture. They are significantly quieter than their two-stroke counterparts and much easier to operate, running on the standard AI-92 gasoline you use in your car. There's no need to constantly mix oil and gasoline, as the oil in these engines is poured separately into the oil sump, significantly reducing fuel consumption.

This is precisely why Honda produces only four-stroke engines and has achieved tremendous success in their production.