Why Electronic Fuel Injection?
Before computers became small, fast, and inexpensive enough to properly manage the metering of fuel into an engine, mechanical devices were devised to accomplish the task. These devices are known as carburetors. Carburetors, while effective, are an inefficient means with which to control the air/fuel (A/F) ratio of intake gases. The amount of fuel dispensed into the intake air stream is dependent strictly on a few mechanical variables such as fuel line pressure, motor RPM, fuel jet flow rate, and intake gas pressure. A fuel dispensing system designed around a carburetor cannot take into account variables such as measured A/F ratio, exhaust gas temperature, throttle position, and mass-air flow. Certain advances had been made in carburetor technology into the early 1980s including electronic jet control (a precursor to electronic fuel injection), but the real revolution was the introduction of electronically controlled valves with fast opening and closing times as well as good fuel atomization.
Electronic Fuel Injection (EFI) works on two major principles. The first is the ability to measure the mass of the air flowing through the intake manifold. The second is the ability to measure the exhaust gas oxygen content. Using sensors for the observation of these variables, a properly programmed EFI system can inject a nearly stoichiometric mix of fuel and air into the motor's cylinder and thus obtain the best combustion and fuel economy characteristics. The system is timed by a cam position sensor and is fine tuned with data from a variety of other sensors including exhaust gas temperature, throttle position, and valve position.
The goal of the system is to obtain a stoichiometric mix of air and fuel such that the chemical reaction of the combustion process leaves neither oxygen or fuel in the exhaust. For more project background and up to date project progress, please check out the Project Updates and SDP Documents sections of the site. For information on the Super-Mileage Competition, Rules, and history, please check out some of our links to SAE's competition site. To get a primer on the operation of a 4-cycle motor, check out the links below to HowStuffWorks.com. Enjoy the site and feel free to contact any of us through Meet the Team.