How a lawn mower engine works
The internal combustion engine that powers a typical lawn mower is identical in its operating principles of the internal combustion engine in your car.
However, the lawn mower engine is much smaller, less powerful and much simpler in design than the typical automobile engine, which makes it easier to control, maintain and repair.
In lawn mowers without an electric starter, a rewind cord is pulled to start the motor running. When the cord is given a sharp tug, the motor rotates the flywheel, a heavy wheel with magnets embedded in it which is attached to the crankshaft of the engine.
As the flywheel rotates, the magnets produce an electric current which is sent to the spark plug. The spark plug provides a spark that ignites the fuel in the cylinder of the engine, the start of the process of combustion and the start of the engine. In mowers with an electric starter, a starter motor does the work of the cord rewind.
Fuel and carburetor
When the engine is running, the fuel is coming from the fuel tank via a fuel line and carburetor. The carburettor is a device that mixes the fuel with air, and introduces the mixture through an intake manifold into the cylinder of the engine.
The airflow (and, indirectly, fuel) is arranged in the carburettor by a throttle valve, which is manually manipulated by the user or automatically operated to maintain the engine at a constant speed.
Compression and ignition
If the air-fuel mixture enters into the cylinder via an inlet valve, it is compressed by an upward stroke of the piston. This compression of the fuel mixture will burn fuel more efficiently.
After the mixture is compressed, the spark plug fires, igniting the fuel mixture burst in a burst of rapidly expanding gas. The expanding gas forces the piston downward, whereby the crankshaft, wherein the piston is connected to, rotates.
The crankshaft is in turn rotates blade of the mower. Bottom of each stroke of the piston momentum carries it up again, from the compression and ignition process again.
Lubrication and cooling
The movement of the engine generates a lot of friction and heat that would quickly destroy the engine if it is not for the lubrication and cooling. Lubrication is of oil in the sump at the base of the motor. Plastic paddles attached to the crankshaft pull oil from the crankcase and provided by the engine.
Heat from the engine is absorbed by metal fins on the cylinder head, cylinder block and flywheel which surface area increase and optimize the air flow around the hot engine parts.
How a Front-self-propelled lawn mower works
Although often significantly more expensive than their non-powered cousins, front wheel self propelled lawn mowers become quite common for one simple reason: they often make odious task of mowing the lawn easier.
With a conventional mower, the operator generates all the power to move the machine around the yard, with nothing but good old sweat equity and muscles. The best self propelled lawn mower has a shaft diverts in the engine power which gives the rotation to the wheels, just like a car.
Internal Combustion Engine
At the heart of the forward movement of a driven lawn mower is the internal combustion engine which is originally made only for rotating blade which cuts the grass flow.
Somewhere along the way, someone on the bright idea to be a part of the power generated by the rotating shaft to move to the front two wheels, reducing the amount of muscle power needed to reduce maintain a lawn. Using a single stroke, gas-powered engine for this purpose was a real genius.
The variable speed
Some operated lawn mowers have only a single speed. As soon as the bar is depressed, it takes off, and moves at a constant speed, regardless of what is released to the beam.
Something fancier and more expensive is the variable speed version, which the operator to determine how much power is used to make the drivetrain and wheels.
Barely pushing the bar only to move the mower a bit by providing a small amount of power. The mower moves quickly if the bar is pressed exponentially more.