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Gas Engine

Chainsaws, one of the most versatile and indispensable tools in the forestry industry and for homeowners, have a diverse range of models and types. They can be powered by electricity, batteries, or gasoline. This article focuses on one particular type: the gas-powered chainsaw. Its engine is a marvel of engineering, delivering the power that makes the chainsaw a formidable tool for cutting through thick tree trunks or heavy lumber.

Gas Engine

What is Gas Engine

A gas engine is an internal combustion engine that runs on a petroleum-based fuel, such as gasoline (petrol) or diesel. Here are some key things to know about gas engines:

  • Fuel Type: Gas engines are designed to burn gasoline, which is a liquid petroleum-based fuel. Gasoline has a high octane rating that allows for higher compression ratios in engines.
  • Combustion Process: In a gas engine, the gasoline fuel is mixed with air and compressed in the cylinders. It is then ignited by a spark plug, causing the gasoline/air mixture to combust. This rapid combustion pushes the piston down in the cylinder.
  • Common Uses: Gasoline/petrol engines are widely used in automobiles, motorcycles, lawn equipment, small engines, and some boats/generators. They provide good power-to-weight ratios for mobile applications.
  • Spark Ignition: Unlike diesel engines which use compression ignition, gas engines use spark plugs to ignite the fuel/air mixture. This requires an electrical system for the spark.
  • Emissions: Gas engines emit harmful pollutants like carbon monoxide, nitrogen oxides, and volatile organic compounds from the combustion of gasoline. Control methods help reduce emissions.
  • Efficiency: Gas engines are somewhat less thermally efficient than diesel engines, usually achieving 20-30% efficiency. But they provide good throttle response.

The Gas Engine: How It Works

Chainsaw Engine: How It Works

Gas chainsaws are powered by two-stroke (also known as two-cycle) engines. Unlike a four-stroke engine, which has a separate stroke for each of the four stages of internal combustion (intake, compression, power, and exhaust), a two-stroke engine combines these processes into just two strokes, hence its name.

In a two-stroke engine, the first stroke, or power stroke, begins with the piston at top dead center (TDC). The spark plug ignites the fuel-air mixture, creating a high-pressure wave that drives the piston downward. This downward movement turns the crankshaft, providing the mechanical power to drive the chainsaw's chain.

As the piston reaches bottom dead center (BDC), the exhaust port opens, allowing the burnt gases from combustion to escape. Almost simultaneously, the intake port opens, admitting a fresh mixture of fuel and air into the cylinder, which is then compressed as the piston begins its upward stroke. As the piston rises and closes off the intake and exhaust ports, the spark plug ignites the compressed fuel-air mixture, starting the cycle anew.

Gas and Oil Mixture

One characteristic of two-stroke engines that sets them apart is their requirement for a gas and oil mixture. Because they lack a dedicated lubrication system, two-stroke engines need oil mixed with the fuel to lubricate the crankcase. This oil prevents friction between the moving parts, which could otherwise lead to overheating and engine failure. Typically, the recommended ratio of gasoline to oil is 50:1, but it can vary based on the manufacturer's specifications.

The Carburetor

A carburetor plays a crucial role in a gas chainsaw engine by mixing air and fuel in the correct proportions for combustion. It provides the engine with the right amount of this mixture based on the speed at which the chainsaw is running. When the operator pulls the throttle, more fuel and air are allowed into the engine, increasing the engine speed and thus, the chain speed.

The carburetor also has a choke, which helps start the engine when it's cold. The choke restricts the amount of air entering the carburetor, enriching the fuel-air mixture and making it easier for the spark plug to ignite.

The Ignition System

The ignition system consists of a spark plug, an ignition coil, and a flywheel with magnets. When the flywheel rotates, it generates a magnetic field that induces a high voltage in the ignition coil. This voltage is transmitted to the spark plug, which generates a spark to ignite the fuel-air mixture in the combustion chamber.

The Exhaust System

The exhaust system directs the combustion gases out of the engine and muffles the noise created by the combustion process. A good exhaust system also helps improve engine performance by creating a slight vacuum that helps draw the fresh fuel-air mixture into the cylinder.

Power, Torque, and Efficiency

Gas chainsaws are popular for their high power-to-weight ratio, torque, and mobility. They are capable of generating considerable power, allowing them to handle heavy-duty cutting tasks. The torque produced by gas engines is also higher compared to electric or battery-powered chainsaws, which means they can maintain their cutting power even under heavy load.

Maintenance and Environmental Impact

Gas chainsaws require more maintenance than their electric counterparts. Regular tasks include refueling, checking the oil mixture, cleaning or replacing the air filter, and adjusting the carburetor. Additionally, two-stroke engines emit more pollutants than four-stroke engines, which is a concern in terms of environmental impact.


The gas engine is the heart of a gas-powered chainsaw, providing the power and torque needed to cut through thick wood quickly and efficiently. While they require more maintenance and have a higher environmental impact than electric or battery-powered chainsaws, their power and mobility make them a preferred choice for many users. With a basic understanding of how the engine works, users can operate their chainsaws more effectively and perform routine maintenance tasks to prolong the lifespan of their tools.

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