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