Power and Emissions
Gasoline-engine powered trimmers usually have a minimum of 21 cc displacement motors. At this size they can easily turn 2-millimetre (0.079 in) line and some have nylon blades as accessories to the line-reel. A 32 cc engine can swing a 2.75 mm (0.108 in) line and often has metal-blade accessories. Most trimmers use two stroke engines and require gasoline mixed with oil. Due to pollution laws four stroke engines are becoming more popular. For instance, Honda, MTD and Craftsman manufacture a four stroke engine trimmer. Other companies, such as John Deere, now carry Low Emission two stroke engine trimmers. Stihl manufactures a hybrid four stroke engine trimmer using a technology called 4MIX. 4MIX trimmers have no oil reservoir. This engine is lubricated using pre-mixed gasoline, like a two stroke engine.
Electric edge trimmers have the advantage of being very light, easy to maneuver and easy-to-operate devices. However, the length of power cord that can be deployed across the ground limits them and they are usually less powerful and robust than the gasoline-engine ones. Electric machines normally are limited to 2.5 mm (0.098 in) maximum diameter nylon because of their lower power output (400 to about 1200 watts). Recently there are electric string trimmers that offer the same performance as gas powered trimmers. Battery powered units are to be recharged after each use. The recharge time is typically several hours long; some models offer a quick charge option that cuts charging time to between 30 minutes and 2 hours, or a removable battery pack so the user can have more than one battery ready to swap out when the first one runs down.
The typical two-cycle engine used on string trimmers pollutes heavily due to incomplete combustion in the cylinder. This results in unburned fuel escaping through the exhaust system and into the environment. US emission standards specifically limit emissions from small engines. Electric models produce no emissions at the point of use. Battery-powered units typically use small or large sealed lead acid, nickel metal hydride, or lithium ion batteries.
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