Man in the Stands

An Engine for your wallet and your world

By: Zack Myers

“Direct injection is designed to get a better fuel economy so it would save the consumer money, but fuel injection was designed to do that,” said Marcus Smith, lead direct injection service technician at Cobb County Kia. “The way we’re going now, direct injection is the way to go.”

The next big thing in automobiles may already be powering the vehicles you see on the road every day, and we are not talking about ethanol. This is about gasoline engines. Direct injected (DI) gasoline engines, to be exact.


(A view under the hood of a DI engine.)

For an engine to work, three things are necessary: fuel, oxygen, and a spark. Both, standard and DI, engines work this way. Where the difference comes in is the delivery of fuel and how the fuel mixes with the oxygen. Though this sounds very simple, the efficiency of the two types is vastly different.

The standard engine, as the world has come to know it, takes a roundabout way to get the fuel into the combustion chamber to burn. First, gas is pumped from the tank, through the fuel line, into injectors that are mounted in the engine. Those injectors spray the fuel into the air intake manifold. Here, the fuel and air make a mixture of a fine mist before a piston descends, sucking the mist into the combustion chamber. Then the piston ascends inside its cylinder to compress the air-fuel mix until it is almost nine times as dense as it began. The cylinder’s spark plug ignites to create an extremely pressurized, intense blast. The pressure pushes the piston down again with incredible power, triggering a turn of the crankshaft to send power to the wheels.

Direct injected engines work much more efficiently by skipping the air intake manifold step. The fuel is pumped straight from the tank, into the injector, and into the combustion chamber. This causes the fuel to be burned where it needs to be burned, helping with fuel economy and emissions.

“As far as emissions, the design is to get better emissions,” said Smith.

“From what I’ve read, direct injected engines are supposed to burn more completely with more air, so there are fewer emissions,” said Ethan Shirley, owner of a Volkswagen Jetta TDI.

Standard engines use a “rich” fuel mixture, meaning that there is a lower ratio of air to fuel in the mix. Direct injected engines allow for a “leaner” mixture, using a 40 parts air to one part fuel, or 40:1, ratio. Standard engines burn a mix that rations out to about 14.7:1. Fuel is burned more cleanly in a leaner mix. The cleaner the fuel is able to burn, the better gas mileage your car will get in the long run according to HowStuffWorks.

“To be honest, it doesn’t burn cleaner,” said Smith. “Like I said, it just directs [the fuel] directly into the cylinder versus into the intake. It’s a faster injection instead of having to go mix with the air and then come in. That’s how it gets better fuel economy.”


(Marcus Smith showing the intricacies under the hood.)

“I have noticed better mileage since switching to a direct injected engine,” said Shirley. “The TDI model, on average, gets a little over 10 more miles per gallon than the non-TDI model Jetta.”

“I didn’t know that the car was direct injected when I bought it, but found out after doing some research,” said Shirley. “My favorite thing I found out when doing my research is how durable the engines are. This engine should be able to take more abuse than a standard engine. Because of how durable these engines are expected to be, I would definitely recommend them.”

The computer systems that run the direct injected engines are running completely different, more sophisticated software than their counterparts.

“We’ve been using computers in cars since, like, 1983. Of course the software gets newer because it has to run different programs especially with the emissions that we have now. [The computer] plays a bigger role but it’s basically the same concept,” said Smith. “The computer regulates how much fuel [is delivered], it times the engine, it puts fuel in at a certain time, it runs a lot of things. They’ve been there for a long time, but it plays a bigger role now. Between the two different engines, the computer is probably the same, but the programming is different because of the timing and the fuel injection.”

Many car manufacturers are introducing lines that use DI engines. General Motors is adding them into its 2014 models of the Chevrolet Corvette Stingray and even in the Chevy Silverado full size pickups. They currently have the 2013 V6 models of the Chevy Camaro using DI technology. Another GM manufacturer using DI technology is Cadillac. Cadillac’s entire line of vehicles, with the exceptions of one sport wagon model and any of its Escalade models, is using direct injection. Ford, another American car producer, has a full line of vehicles using DI. Any of the cars that boast to have “Ecoboost” technology have DI engines in them.

Marcus Smith also said that he has yet to see any more problems out of direct injected vehicles as opposed to their standard counterparts, which is good considering how many manufacturers are beginning to implement these motors into their lines of cars.

“All cars have issues,” said Smith with a smile.

The American automobile producers are not the only ones implementing the use of these engines. The manufacturer of Mr. Shirley’s Jetta, the Volkswagen Group, headquartered in Berlin, Germany, has been using the technology for some time now. They produce Volkswagen and Audi, among others. The difference in these models that use DI is that Volkswagen and Audi use clean diesel as opposed to gasoline. They list their lines as “TDI,” or Turbocharged Direct Injection. By turbocharging the engine and using direct injection, the company is able to use smaller engines to increase fuel economy. For example, the base model of the Volkswagen Passat TDI SE uses a 2.0 liter engine, allowing the car to get 43 miles per gallon and 795 miles per tank.

Why does Smith say that DI is the way to go? For him, it is about the long term savings at the pump.

“Overall, over a year, you’re going to save more money on your fuel,” said Smith. “It doesn’t get a better burn, per se, but it runs better.”

Smith does give one way that everyone can gain gas mileage with the car they already have.

“The way to get a better fuel economy is to use a higher grade of gas. The higher grade gas burns better because you don’t have all of the additives in it. The 93 [grade] is the best thing you can get. It’s a pure gas. That’s how you really get better fuel economy.”

How do you feel about making the switch to a direct injected engine against the standard engine that you are already driving? Would you make the switch or just use Mr. Smith’s advice and use higher grade gasoline? What reasons do you feel are worth switching for?


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