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Most trimmers use single-cylinder engines (particularly two-stroke) and require gasoline mixed with oil. Due to pollution laws four stroke engines are becoming more popular, particularly in the commercial market. Manufacturers include Honda, MTD and Craftsman. Companies such as John Deere carry low-emission two-stroke engine trimmers.
The most common self-contained power source for lawn mowers is a small 4-stroke (typically one-cylinder) internal combustion engine. Smaller mowers often lack any form of self-propulsion, requiring human power to move over a surface; "walk-behind" mowers are self-propelled, requiring a human only to walk behind and guide them.
Four-stroke cycle used in gasoline/petrol engines: intake (1), compression (2), power (3), and exhaust (4). The right blue side is the intake port and the left brown side is the exhaust port. The cylinder wall is a thin sleeve surrounding the piston head which creates a space for the combustion of fuel and the genesis of mechanical energy.
The four-stroke engine is more efficient when running at full throttle, while the opposite is the case for the two-stroke engine. When a small car under heavy load runs at half speed, the engine automatically switches to the two-cycle mode, which is then more efficient. The research on this showed a 27% reduction in fuel consumption. [8] [9]
The combustion cycle can be either two-stroke (which results in a lighter engine for a given power output) [3] [4] or four-stroke (which produce lower levels of exhaust gas emissions). [5] [6] The fuel is usually either petrol or diesel. [7] In 1973, a small Wankel (rotary) engine manufactured by NSU was used in a lawn mower. [8]
A stroke is the movement of a piston from TDC to BDC or vice versa, together with the associated process. While an engine is in operation, the crankshaft rotates continuously at a nearly constant speed. In a 4-stroke ICE, each piston experiences 2 strokes per crankshaft revolution in the following order.