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Speaker 1: Welcome to brain Stuff from how stuff works dot com

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Speaker 1: where smart happens. Hi. I'm Marshall Brain with today's question,

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Speaker 1: how do direct injection two stroke engines work? A couple

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Speaker 1: of weeks ago we talked about gasoline direct injection engines.

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Speaker 1: These are four stroke engines that are starting to appear

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Speaker 1: in cars from every major manufacturer. These engines get better

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Speaker 1: gas mileage by allowing higher compression ratios and leaner mixtures.

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Speaker 1: A reader named Chris wrote in and suggested that I

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Speaker 1: check out Evan roods E Tech engines. These used direct

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Speaker 1: injection technology on two stroke engines. Two stroke engines are

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Speaker 1: the kind of engines you normally find on boats, for example,

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Speaker 1: little outboard motors. Also you find them on weed whackers

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Speaker 1: and chainsaws. But a lot of these have been phased

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Speaker 1: out because as they're dirty, they tend to put a

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Speaker 1: lot of oil and exhaust emissions into the atmosphere. But

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Speaker 1: if you could figure out a way around those problems,

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Speaker 1: two stroke engines have two huge advantages over four stroke engines. First,

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Speaker 1: two stroke engines are much lighter than four stroke engines

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Speaker 1: of the same power, and second, two stroke engines are

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Speaker 1: much simpler, usually meaning less maintenance. The reason why you

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Speaker 1: get more power out of the weight is because at

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Speaker 1: two stroke engine fires every two strokes, where a four

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Speaker 1: stroke engine fires only once every four strokes, so you

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Speaker 1: have twice as many power strokes coming out of a

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Speaker 1: two stroke engine in a given amount of time. That

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Speaker 1: means you have twice as much power potentially for the

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Speaker 1: same size engine. The simplicity and also some of the

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Speaker 1: weight savings comes from the fact that there's no valve

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Speaker 1: train in a two stroke engine, meaning no camshaft, no valves,

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Speaker 1: no stalve springs, no timing chain or belt, and so on. Therefore,

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Speaker 1: the advantage of a direct injection two stroke engine would

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Speaker 1: be the greatly reduced weight of the two stroke design,

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Speaker 1: while at the same time eliminating all the pollution produced

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Speaker 1: by a normal carbureted two stroke and increasing the efficiency.

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Speaker 1: So how did Evan Rude convert a normal carburetted two

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Speaker 1: stroke engine into a direct injection two stroke engine. Basically,

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Speaker 1: they simply took off the carburetor and added a fuel

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Speaker 1: injector into the combustion chamber, so it can directly inject

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Speaker 1: fuel into the combustion chamber just like a direct injection

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Speaker 1: four stroke engine, but in the two stroke design. This

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Speaker 1: has the advantage of completely eliminating the need to mix

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Speaker 1: oil with the gasoline, and that gets rid of both

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Speaker 1: the exhaust from unburned gasoline and the exhaust from unburned oil,

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Speaker 1: and it radically increases the efficiency. Now two stroke engines

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Speaker 1: probably are twice as efficient. They would get twice the

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Speaker 1: miles per gallon, for example, that an old style two

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Speaker 1: stroke engine gets. If you've ever used a two stroke engine,

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Speaker 1: having heard this description, there's now a question in your mind,

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Speaker 1: how does the engine get lubricated? Because in a normal

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Speaker 1: two stroke engine, you mix the oil in with the gasoline.

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Speaker 1: That oil gas mixture goes into the crank case, and

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Speaker 1: a normal two stroke engine is using the crank case

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Speaker 1: as an air pump. It lubricates the crankshaft bearings and

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Speaker 1: the cylinder walls and keeps the engine running smoothly. That

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Speaker 1: oil then gets burned when the engine sucks the gasolate

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Speaker 1: lane an oil mixture into the combustion chamber, or most

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Speaker 1: of it gets burned anyway. Now, with direct injection, you

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Speaker 1: don't have to mix the oil and gas. So what

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Speaker 1: lubricates the engine? The evan root engine can't use a

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Speaker 1: sub system like a normal four stroke engine would because

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Speaker 1: the crank case and the two stroke engine is still

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Speaker 1: acting like an air compressor, and you can't mix the

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Speaker 1: oil with the gas as in a traditional two strokes

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Speaker 1: since the gas never makes it into the crank case.

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Speaker 1: To lubricate the crank shaft of the cylinder wall. In

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Speaker 1: an E tech engine, they use an external oil tank

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Speaker 1: that holds about two liters of oil, enough for about

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Speaker 1: forty hours of operation. The oil is slowly injected into

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Speaker 1: the places that need oil, like the crank bearings and

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Speaker 1: the cylinder wall. Therefore, the oil does mix with the

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Speaker 1: air getting pumped through the crank case, but in a

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Speaker 1: much smaller quantity, and it does get burned in the

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Speaker 1: combustion process, but because it's in such a smaller quantity,

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Speaker 1: it doesn't really have a significant effect. In fact, the

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Speaker 1: amount of oil is so small that it has no

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Speaker 1: noticeable effect on emissions and it has none of the

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Speaker 1: pass through problems with oil as in a carbureted two stroke. Also,

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Speaker 1: note that by burning the oil there are environmental advantages.

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Speaker 1: There's no pollution potential when changing the crank case oil

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Speaker 1: of a four stroke engine. For example, a person changing

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Speaker 1: a four stroke engines oil their cars. Oil, for example,

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Speaker 1: might spill or dump the oil on the ground or

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Speaker 1: in water, and there's no possibility of forgetting to change

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Speaker 1: the oil and ruining the engine. The engine won't operate

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Speaker 1: once that external tank of oil goes empty. For more

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Speaker 1: on this and thousands of other topics, does it how

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