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Hi.

I'm Marshall Brain with today's question, how do direct injection two stroke engines work?

A couple of weeks ago we talked about gasoline direct injection engines.

These are four stroke engines that are starting to appear in cars from every major manufacturer.

These engines get better gas mileage by allowing higher compression ratios and leaner mixtures.

A reader named Chris wrote in and suggested that I check out Evan roods E Tech engines.

These used direct injection technology on two stroke engines.

Two stroke engines are the kind of engines you normally find on boats, for example, little outboard motors.

Also you find them on weed whackers and chainsaws.

But a lot of these have been phased out because as they're dirty, they tend to put a lot of oil and exhaust emissions into the atmosphere.

But if you could figure out a way around those problems, two stroke engines have two huge advantages over four stroke engines.

First, two stroke engines are much lighter than four stroke engines of the same power, and second, two stroke engines are much simpler, usually meaning less maintenance.

The reason why you get more power out of the weight is because at two stroke engine fires every two strokes, where a four stroke engine fires only once every four strokes, so you have twice as many power strokes coming out of a two stroke engine in a given amount of time.

That means you have twice as much power potentially for the same size engine.

The simplicity and also some of the weight savings comes from the fact that there's no valve train in a two stroke engine, meaning no camshaft, no valves, no stalve springs, no timing chain or belt, and so on.

Therefore, the advantage of a direct injection two stroke engine would be the greatly reduced weight of the two stroke design, while at the same time eliminating all the pollution produced by a normal carbureted two stroke and increasing the efficiency.

So how did Evan Rude convert a normal carburetted two stroke engine into a direct injection two stroke engine.

Basically, they simply took off the carburetor and added a fuel injector into the combustion chamber, so it can directly inject fuel into the combustion chamber just like a direct injection four stroke engine, but in the two stroke design.

This has the advantage of completely eliminating the need to mix oil with the gasoline, and that gets rid of both the exhaust from unburned gasoline and the exhaust from unburned oil, and it radically increases the efficiency.

Now two stroke engines probably are twice as efficient.

They would get twice the miles per gallon, for example, that an old style two stroke engine gets.

If you've ever used a two stroke engine, having heard this description, there's now a question in your mind, how does the engine get lubricated?

Because in a normal two stroke engine, you mix the oil in with the gasoline.

That oil gas mixture goes into the crank case, and a normal two stroke engine is using the crank case as an air pump.

It lubricates the crankshaft bearings and the cylinder walls and keeps the engine running smoothly.

That oil then gets burned when the engine sucks the gasolate lane an oil mixture into the combustion chamber, or most of it gets burned anyway.

Now, with direct injection, you don't have to mix the oil and gas.

So what lubricates the engine?

The evan root engine can't use a sub system like a normal four stroke engine would because the crank case and the two stroke engine is still acting like an air compressor, and you can't mix the oil with the gas as in a traditional two strokes since the gas never makes it into the crank case.

To lubricate the crank shaft of the cylinder wall.

In an E tech engine, they use an external oil tank that holds about two liters of oil, enough for about forty hours of operation.

The oil is slowly injected into the places that need oil, like the crank bearings and the cylinder wall.

Therefore, the oil does mix with the air getting pumped through the crank case, but in a much smaller quantity, and it does get burned in the combustion process, but because it's in such a smaller quantity, it doesn't really have a significant effect.

In fact, the amount of oil is so small that it has no noticeable effect on emissions and it has none of the pass through problems with oil as in a carbureted two stroke.

Also, note that by burning the oil there are environmental advantages.

There's no pollution potential when changing the crank case oil of a four stroke engine.

For example, a person changing a four stroke engines oil their cars.

Oil, for example, might spill or dump the oil on the ground or in water, and there's no possibility of forgetting to change the oil and ruining the engine.

The engine won't operate once that external tank of oil goes empty.

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