WEBVTT - How do gasoline direct injection engines work?

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<v Speaker 1>Welcome to Brainstuff from how stuff works dot com where

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<v Speaker 1>smart Happens. Hi Marshall Brain with today's question, how do

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<v Speaker 1>the new gasoline direct injection engines work and what are

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<v Speaker 1>the advantages? Think about the internal combustion gasoline engine. We

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<v Speaker 1>have a love hate relationship with it. It creates a

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<v Speaker 1>lot of pollution, It's incredibly inefficient, It spews carbon into

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<v Speaker 1>the atmosphere. It makes us dependent on crude oil, with

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<v Speaker 1>negative side effects like oil spills and trade imbalances. Yet

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<v Speaker 1>we're completely dependent on the internal combustion engine. Nearly every

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<v Speaker 1>car on the road today in America has one, and

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<v Speaker 1>they will be with us for some time to come.

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<v Speaker 1>Have you ever wondered why? There are four things about

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<v Speaker 1>the internal combustion engine that make it the engine of

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<v Speaker 1>choice in the vast majority of our cars. First, and

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<v Speaker 1>probably most importantly, it is reliable. A typical engine will

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<v Speaker 1>last at least a hundred thousand miles if you take

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<v Speaker 1>care of it, and it will do its job in

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<v Speaker 1>the hottest deserts and the coldest winters. Second, relatively speaking,

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<v Speaker 1>it doesn't weigh much for the power it produces. An

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<v Speaker 1>electric motor and its battery pack way a lot more.

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<v Speaker 1>The same could be said for the cost of the engine.

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<v Speaker 1>Batteries are really expensive right now. And finally, you can

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<v Speaker 1>recharge and internal combustion engine by filling the gas tank.

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<v Speaker 1>That process only takes a couple of minutes. For an

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<v Speaker 1>electric car, it takes hours and hours to recharge, making

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<v Speaker 1>it impractical for any kind of long road trip. If

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<v Speaker 1>we could invent cheap, light fast recharge batteries, the internal

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<v Speaker 1>combustion engine would die. If we can invent fuel cells

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<v Speaker 1>that are inexpensive and reliable, the internal combustion engine would die.

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<v Speaker 1>But right now there's nothing that comes close to the

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<v Speaker 1>internal combustion engine, even with all its problems. So car

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<v Speaker 1>manufacturers are trying to improve the internal combustion engine, a

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<v Speaker 1>process that's been going on for a hundred years, and

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<v Speaker 1>the latest incarnation is pretty remarkable. It's called gasoline direct injection,

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<v Speaker 1>and it should make it possible to get cars up

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<v Speaker 1>to seventy miles per gallon or so even before adding

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<v Speaker 1>a hybrid drive. Just about every major manufacturer will be

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<v Speaker 1>releasing some type of gasoline direct injection technology in two

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<v Speaker 1>thousand eleven. If you look across the claims from all

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<v Speaker 1>of the different companies, there are several common threads and

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<v Speaker 1>what they're doing. The engines all use a new type

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<v Speaker 1>of fuel injector that can spray fuel directly into the

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<v Speaker 1>cylinder during the compression stroke. To do that, they all

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<v Speaker 1>need extremely high pressure fuel pumps rated at something around

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<v Speaker 1>two thousand p s i in current cars. The fuel

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<v Speaker 1>injection technlogy being used is called port fuel injection, where

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<v Speaker 1>the injector sprays fuel at low pressure into the intake manifold.

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<v Speaker 1>The direct injection process allows the fuel to evaporate in

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<v Speaker 1>the cylinder and cool the air fuel mixture that helps

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<v Speaker 1>avoid premature ignition. So these engines can increase the compression ratio.

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<v Speaker 1>Mazda's new direct injection engine, for example, goes up to

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<v Speaker 1>a fourteen to one compression ratio, which has never been

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<v Speaker 1>seen before in a production gasoline engine. The normal high

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<v Speaker 1>has been twelve to one or so, and that would

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<v Speaker 1>require premium fuel in the past. Many of the engines

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<v Speaker 1>are using multiple injector sprays per stroke. One spray occurs

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<v Speaker 1>as the air starts flowing in on the intake stroke

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<v Speaker 1>to cool things down. The second occurs right before the

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<v Speaker 1>spark plug fires. This creates a stratified charge in the

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<v Speaker 1>cylinder for a better burn pattern using less fuel. The

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<v Speaker 1>high compression ratio also allows more energy to be extracted

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<v Speaker 1>from the gasoline. Think of it this way. When gasoline

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<v Speaker 1>burns in a higher compression environment, it gets to expand further,

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<v Speaker 1>meaning that more work can be extracted from that expansion.

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<v Speaker 1>The stratified charge allows less fuel to be injected while

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<v Speaker 1>still getting a good ignition and burn pattern. It allows

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<v Speaker 1>a much leaner mixture in the cylinder. One of the

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<v Speaker 1>key technologies making gasoline direct injection possible is new piezoelectric

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<v Speaker 1>fuel injectors. They're extremely precise and extremely fast. They also

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<v Speaker 1>provide an unexpected side effect In some cases. With these injectors,

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<v Speaker 1>it's possible to start a warm engine without using the

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<v Speaker 1>starter motor. The computer can find a cylinder that has

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<v Speaker 1>its piston in the right position, inject fuel, and fire

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<v Speaker 1>it to start the engine. This start stoppability should make

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<v Speaker 1>it easier for car manufacturers to create ours that no

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<v Speaker 1>longer need to idle at traffic lights, and that'll save

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<v Speaker 1>a lot of fuel while eliminating lots of urban pollutions. Again,

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<v Speaker 1>stop and go traffic for more illness, and thousands of

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