Speaker 1: Welcome to Brainstuff from how stuff works dot com where
Speaker 1: smart Happens. Hi Marshall Brain with today's question, how do
Speaker 1: the new gasoline direct injection engines work and what are
Speaker 1: the advantages? Think about the internal combustion gasoline engine. We
Speaker 1: have a love hate relationship with it. It creates a
Speaker 1: lot of pollution, It's incredibly inefficient, It spews carbon into
Speaker 1: the atmosphere. It makes us dependent on crude oil, with
Speaker 1: negative side effects like oil spills and trade imbalances. Yet
Speaker 1: we're completely dependent on the internal combustion engine. Nearly every
Speaker 1: car on the road today in America has one, and
Speaker 1: they will be with us for some time to come.
Speaker 1: Have you ever wondered why? There are four things about
Speaker 1: the internal combustion engine that make it the engine of
Speaker 1: choice in the vast majority of our cars. First, and
Speaker 1: probably most importantly, it is reliable. A typical engine will
Speaker 1: last at least a hundred thousand miles if you take
Speaker 1: care of it, and it will do its job in
Speaker 1: the hottest deserts and the coldest winters. Second, relatively speaking,
Speaker 1: it doesn't weigh much for the power it produces. An
Speaker 1: electric motor and its battery pack way a lot more.
Speaker 1: The same could be said for the cost of the engine.
Speaker 1: Batteries are really expensive right now. And finally, you can
Speaker 1: recharge and internal combustion engine by filling the gas tank.
Speaker 1: That process only takes a couple of minutes. For an
Speaker 1: electric car, it takes hours and hours to recharge, making
Speaker 1: it impractical for any kind of long road trip. If
Speaker 1: we could invent cheap, light fast recharge batteries, the internal
Speaker 1: combustion engine would die. If we can invent fuel cells
Speaker 1: that are inexpensive and reliable, the internal combustion engine would die.
Speaker 1: But right now there's nothing that comes close to the
Speaker 1: internal combustion engine, even with all its problems. So car
Speaker 1: manufacturers are trying to improve the internal combustion engine, a
Speaker 1: process that's been going on for a hundred years, and
Speaker 1: the latest incarnation is pretty remarkable. It's called gasoline direct injection,
Speaker 1: and it should make it possible to get cars up
Speaker 1: to seventy miles per gallon or so even before adding
Speaker 1: a hybrid drive. Just about every major manufacturer will be
Speaker 1: releasing some type of gasoline direct injection technology in two
Speaker 1: thousand eleven. If you look across the claims from all
Speaker 1: of the different companies, there are several common threads and
Speaker 1: what they're doing. The engines all use a new type
Speaker 1: of fuel injector that can spray fuel directly into the
Speaker 1: cylinder during the compression stroke. To do that, they all
Speaker 1: need extremely high pressure fuel pumps rated at something around
Speaker 1: two thousand p s i in current cars. The fuel
Speaker 1: injection technlogy being used is called port fuel injection, where
Speaker 1: the injector sprays fuel at low pressure into the intake manifold.
Speaker 1: The direct injection process allows the fuel to evaporate in
Speaker 1: the cylinder and cool the air fuel mixture that helps
Speaker 1: avoid premature ignition. So these engines can increase the compression ratio.
Speaker 1: Mazda's new direct injection engine, for example, goes up to
Speaker 1: a fourteen to one compression ratio, which has never been
Speaker 1: seen before in a production gasoline engine. The normal high
Speaker 1: has been twelve to one or so, and that would
Speaker 1: require premium fuel in the past. Many of the engines
Speaker 1: are using multiple injector sprays per stroke. One spray occurs
Speaker 1: as the air starts flowing in on the intake stroke
Speaker 1: to cool things down. The second occurs right before the
Speaker 1: spark plug fires. This creates a stratified charge in the
Speaker 1: cylinder for a better burn pattern using less fuel. The
Speaker 1: high compression ratio also allows more energy to be extracted
Speaker 1: from the gasoline. Think of it this way. When gasoline
Speaker 1: burns in a higher compression environment, it gets to expand further,
Speaker 1: meaning that more work can be extracted from that expansion.
Speaker 1: The stratified charge allows less fuel to be injected while
Speaker 1: still getting a good ignition and burn pattern. It allows
Speaker 1: a much leaner mixture in the cylinder. One of the
Speaker 1: key technologies making gasoline direct injection possible is new piezoelectric
Speaker 1: fuel injectors. They're extremely precise and extremely fast. They also
Speaker 1: provide an unexpected side effect In some cases. With these injectors,
Speaker 1: it's possible to start a warm engine without using the
Speaker 1: starter motor. The computer can find a cylinder that has
Speaker 1: its piston in the right position, inject fuel, and fire
Speaker 1: it to start the engine. This start stoppability should make
Speaker 1: it easier for car manufacturers to create ours that no
Speaker 1: longer need to idle at traffic lights, and that'll save
Speaker 1: a lot of fuel while eliminating lots of urban pollutions. Again,
Speaker 1: stop and go traffic for more illness, and thousands of
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