News You Can Use For December 2005 Most small, hand-carried lawn and garden tools such as string trimmers and chainsaws use 2-stroke engines, while larger machines such as lawn and garden tractors use 4-stroke engines. Lawn mowers are available with either type of engine. LSU AgCenter engineer Dr. Dick Parish explains the differences and why 2-stroke engines are more commonly used on small tools. "Most people use the terms ‘2-cycle’ or ‘4-cycle’ to describe the two engine types," Parish says. "This common terminology, while readily understood, is incorrect." The engineer says that every reciprocating internal combustion engine operates through a "cycle" of five functions – intake, compression, ignition, combustion and exhaust. In a 2-stroke engine, all five functions of the cycle are completed in only two strokes of the piston (or one revolution of the crankshaft). In a 4-stroke engine, the five functions require four strokes of the piston (or two revolutions of the crankshaft). Parish says 2-stroke engines aren’t lubricated by a reservoir in the crankcase but by oil mixed with the gasoline. Much of this oil is not burned by the engine and is expelled with the exhaust gas, thus increasing emissions and smoke. He also says the power-to-weight ratio of 2-stroke engines is higher than most 4-stroke engines, so the lighter 2-stroke engines work well in hand-carried applications such as blowers and string trimmers. "Typically, 2-stroke engines rev up to higher speeds than 4-stroke engines, and this accounts for much of the higher power per pound," Parish says. "Also, small 2-stroke engines use intake and exhaust ports instead of valves, thus saving the weight and cost of a valve train. Parish adds that spark plug fouling is more common on 2-stroke engines because of the oil in the fuel, meaning more frequent spark plug changes may be needed. The engineer says 4-stroke engines are lubricated by oil in the crankcase, so oil isn’t mixed with the gasoline. "On small engines, such as those used on lawnmowers, a tab on the bottom of the piston rod splashes oil up into the cylinder," he says. "On larger engines, such as those used on garden tractors, an oil pump distributes the oil under pressure and through an oil filter." Parish cautions that different engine manufacturers recommend different oil mix ratios for their engines. "If you have more than one 2-stroke engine and they aren’t the same brand, you may need to keep separate fuel-to-oil mixes for the machines," he says. Typical ratios range from 32 to 1 (gasoline to oil) to 50 to 1. "You can buy small containers of oil that are measured to provide the right amount of oil for a gallon of gasoline for a given recommended mix ratio," Parish says. "But buying oil in larger quantities may be more economical." Another concern Parish cautions about is having trouble finding a small container measured for the ratio you require unless you go back to the dealer. Most hardware stores, garden centers, discount stores and similar stores carry only one or two ratios. "Don’t just assume that the small container of 2-cycle oil you pick up at the discount store will give the right ratio for your engine," Parish warns. "Check the ratio on the label. It’s helpful to know how much oil you need for your required ratio in case you don’t have the correct measured container." Parish recommends starting with a clean, empty container and pouring in the correct amount of oil. Next, add 1 gallon of gasoline, close the container and shake it to mix the fuel. Agitate the container before pouring each time you use the gasoline mix. "Either type of engine can do a good job if used in an appropriate application," Parish says. "If you have a 2-stroke engine, be sure to mix the oil and gas correctly." ### Contact: Dick Parish at (985)
543-4125 or The difference between a 2-cycle engine and 4-cycle engine is the 2-cycle only needs one revolution of the crankshaft to get to a power stroke, while a 4-cycle engine needs 2 revolutions. To help explain the two different types of engines we will need to explain how each type of engine works first. A two-cycle engine piston has only two strokes. The piston starts at top dead center (TDC) in its bore. As the piston moves down, the piston bore there is an exposed exhaust port and any exhaust is expelled from the cylinder, and as the piston continues to go down there is an intake port exposed when the piston reaches close to bottom dead center (BDC). As the exhaust is expelled, the intake port will let in the air fuel mixture till BDC is reached. As the piston starts going up, the piston covers the intake port then the exhaust port. As the piston continues to go up toward TDC, it is compressing the fuel and air mixture brought in from the intake port. Once TDC is reached, the compressed mixture is ignited by a spark plug. This ignites the mixture and produces the power stroke pushing the piston down toward BDC again. As the piston goes down producing power, when the exhaust port is exposed the remaining pressure is expelled as exhaust. The exhaust leaving the cylinder allows the in-rush of fuel and air to come into the cylinder via the intake port. The complete process is in one revolution of the crankshaft. Every time the piston is going down is a power stroke. When the piston is almost to BDC, it expels the exhaust and intakes the fuel and air. Going up is the compression stroke of the mixture. A four-cycle engine has to make two complete revolutions of the crankshaft. The piston starts at TDC and as the piston starts to go down for its intake stroke, the intake valve opens to let in the fuel and air mixture all the way till BDC of the piston stroke. The intake valve closes and the piston travels to TDC compressing the mixture. This is the compression stroke. Then the mixture is ignited by a spark plug and this explosion pushes the piston down for the power stroke. The piston then travels to BDC. As the piston starts to come back up on its exhaust stroke, the exhaust valve is opened and the exhaust is expelled out the exhaust valve until the engine gets back to TDC. The intake stroke starts the cycle again. Both of these types of engines can be found on gasoline and diesel engines. The diesel and gasoline engines work using the same principle, except the gasoline engine uses spark ignition and diesel uses compression ignition. What is better 2As a general rule, fewer parts equals less potential for failure and easier maintenance. Overall, the 2-cycle engine is typically smaller in displacement and size as compared to 4-cycle which, many times, is almost double the displacement and overall size to achieve the same power.
Can I use 4Using a 4-stroke oil in a 2-stroke engine can therefore disrupt combustion and cause smoke formation and engine degradation.
How do you know if you have a 2A 2-cycle engine has one fill port with a cap that has fuel pump and oil can icon. The cap will usually state the oil to fuel mix ratio. A 4-cycle engine has two fill ports with each cap separately identifying the fuel tank from the oil sump.
Do 4Most lawn mowers have a four-stroke engine, these require fresh unleaded gasoline with an octane rating of 87 or higher. You can use gas with ethanol, but more than 10 percent ethanol is typically not recommended.
|
Whats the difference between 2 cycle and 4 cycle engines
Related Posts
Copyright © 2024 hanghieugiatot Inc.
