Technology: Fuel Injection System

What Is Fuel Injection

In the beginning, gas powered vehicles used a carburetor to get gas into the engine. This worked well, but when fuel injection came along, things changed quickly. Fuel injection, especially electronic fuel injection produces fewer emissions and greatly increases gas mileage.

The carburetor was an ingenious invention in itself. Your car's engine has 4 cycles, and one of them is a "suck" cycle. Put simply, the engine sucks (creates extreme vacuum inside the cylinder) and when it does, the carburetor was there to let the right amount of gas and air get sucked into the engine. While great, this system lacked the precision of a pressurized injection system.

Enter fuel injection. Your engine still sucks, but instead of relying on the suck, fuel injection shoots exactly the right amount of fuel into the chamber. Fuel injection systems have gone through a few evolutions, adding electronics was a big step, but the idea has remained the same: an electrically activated valve (the injector) spraying a metered amount of fuel into your engine.

Single Port Fuel Injection:-

Single port fuel injection systems spray gas into a central intake, that then sucks the gas and air into the engine all at once. This was sort of an in-between invention that combined a carburetor and fuel injection. Most European and Japanese cars skipped this step and went directly to multi-port fuel injection, while American makes used it.

Multi Port Fuel Injection:-

Multi-port injection is still widely in use today. So far it's the most efficient method of metering gas into the engine. Multi-port fuel injection, also known as MFI, consists of an injector for each cylinder in the engine. This injector sprays fuel directly through the intake valve or valves into the combustion chamber. Each injector is activated separately by wire. Early versions of this system, such as CIS, Jetronic and Motronic utilized a fuel distributor that metered fuel to the injectors through separate fuel lines. Later versions utilize a single fuel line that connects to a fuel rail on top of the engine. The injectors take gas from the central fuel rail and squirt it into the engine when told to do so.

Direct fuel injection defined:-

Direct fuel injection is a fuel-delivery technology that allows gasoline engines to burn fuel more efficiently, resulting in more power, cleaner emissions, and increased fuel economy.

How direct fuel injection works:-

Gasoline engines work by sucking a mixture of gasoline and air into a cylinder, compressing it with a piston, and igniting it with a spark; the resulting explosion drives the piston downwards, producing power. Traditional (indirect) fuel injection systems pre-mix the gasoline and air in a chamber just outside the cylinder called the intake manifold. In a direct-injection system, the air and gasoline are not pre-mixed; air comes in via the intake manifold, while the gasoline is injected directly into the cylinder.

Advantages of direct fuel injection

Combined with ultra-precise computer management, direct injection allows more accurate control over fuel metering (the amount of fuel injected) and injection timing (exactly when the fuel is introduced into the cylinder). The location of the injector also allows for a more optimal spray pattern that breaks the gasoline up into smaller droplets. The result is more complete combustion -- in other words, more of the gasoline is burned, which translates to more power and less pollution from each drop of gasoline.

Direct Injection Diesel:-

With diesel engines making a comeback, there has been more focus in recent years on diesel efficiency. Direct injection diesel engines utilize an injector that sprays fuel directly past the glow plug into the combustion chamber. The technology developed here allows for more complete burning of the diesel fuel, and thus better efficiency and less stinky smoke discharged into the atmosphere.

Measuring the Air:-

How do fuel injection systems know how much gas to squirt anyway? Somewhere along the line, somebody (probably at Bosch) realized that you could measure how much gas your engine needed by how much air it was sucking in. Once your engine starts, the measuring of air begins. Early fuel injection systems used a vane system, which was basically a flap inside a tube, to measure how much air was being sucked.

Later systems use a "hot wire" to figure it out. When you turn your engine on, the wire becomes red hot. As air is sucked past this wire, it gets a little cooler. The car's brain measures exactly how much cooler it's getting and uses this number to figure out how much air it's sucking. Then it squirts the correct amount of fuel into the engine.

There are lots and lots of variations to fuel injection systems. We've got electrnic fuel injection, mechanical fuel injection, systems with one oxygen sensor, systems with four oxygen sensors ... but the basics remain the same.

Advantages of direct fuel injection:-

Disadvantages of direct fuel injection:-

The primary disadvantages of direct injection engines are complexity and cost. Direct injection systems are more expensive to build because their components must be more rugged -- they handle fuel at significantly higher pressures than indirect injection systems and the injectors themselves must be able to withstand the heat and pressure of combustion inside the cylinder.

How much more powerful and efficient is direct injection?

Cadillac sells the CTS with both indirect and direct injection versions of its 3.6 liter V6 engine. The indirect engine produces 263 horsepower and 253 lb-ft of torque, while the direct version develops 304 hp and 274 lb-ft. Despite the additional power, EPA fuel economy estimates for the direct injection engine are 1 MPG higher in the city (18 MPG vs 17 MPG) and equal on the highway. Another advantage: Cadillac's direct injection engine runs on regular (87 octane) gasoline. Competing cars from Infiniti and Lexus, which use 300 hp V6 engines with indirect injection, require premium fuel.

Renewed interest in direct fuel injection:-

Direct injection technology has been around since the mid-20th century; however, few automakers adopted it for mass-market cars. Electronically-controlled indirect fuel injection did the job nearly as well at a significantly lower cost, and offered huge advantages over the mechanical carburetor, which was the dominant fuel delivery system until the 1980s. However, recent developments such as skyrocketing fuel prices and stricter fuel economy and emissions legislation have led many automakers to begin developing direct fuel injection systems. You can expect to see more and more cars make use of direct injection in the near future.

Diesels and direct fuel injection:-

Virtually all diesel engines use direct fuel injection. However, because diesels use a different process to combust their fuel (gasoline engines compress a mixture of gasoline and air and ignite it with a spark; diesels compress air only, then spray in fuel which is ignited by the heat and pressure), their injection systems differ in design and operation from gasoline direct fuel injection systems.