Tuesday, March 20, 2012

Fuel Injection: Welcome to 1990

Guest Post Contributed By Jenny Sigelko


E.F.I. is new to NASCAR and still working out the bumps in the road but really,
it is a long overdue concept.
Credit: Jerry Markland/Getty Images for NASCAR

This year, NASCAR has transitioned to a fuel injector system (EFI) instead of the traditional (and outdated) carburetor. Understanding EFI isn’t as complex as you think, in fact, nearly every car made since the 90’s is fuel injected. Think of an engine cylinder as a fast food drink cup except the bottom is movable. Now, imagine that you have 4 straws in the top, punched through the lid at 4 different spots. One straw will be for air, one straw for fuel, one for the spark plug and the final one for exhaust.

This year, the fuel pump that brings fuel from the fuel tank to the engine operates at a much higher pressure. The fuel is kept under pressure in a fuel rail, waiting for each injector to open and allow fuel into our cup (cylinder). The injector is merely a column with a plate at the end. This plate has several (4,8 or more) very tiny holes in it. A pintle in the column moves out of the way when the injector is commanded to open. A major difference this year is the addition of all the electronics that allow the valves and injectors to open and close at the right time. In a production car, the calibration of these events is extremely critical to meeting driveability and emissions concerns, in race cars ensuring consistent operation is most important.

Back to our cup… imagine the bottom of the cup is moving toward the lid:the volume of the cup is getting smaller. At the right time, the intake straw will open allowing air into the cup, next the fuel straw will open allowing very finely atomized fuel to enter the cup. The spark straw fires, igniting the fuel and air driving the bottom of the cup downward and creating power. The exhaust straw opens to let the burned air/fuel mixture out and allowing the cycle to start over again.

Though I haven’t heard any statistics, fuel injectors increase fuel economy. Most every team has had to start over with their fuel calculations and their data models. IndyCar and other series have already changed to fuel injectors. They have had some learning issues as well. Some of the issues may have been in the electronics telling the injectors what to do, some issues may be related to the fuel blend that NASCAR uses, some may be in the fuel pump in the tank and its durability. There may be more failures, made higher profile due to the recent introduction, however these will become as commonplace as any other engine component failure. 

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