PERFECTING DIRECT-INJECTION FUEL SPRAY KEY TO ECOBOOST ENGINE
“¢ Ford’s combustion team finds solutions to ensure faster cold starts and more-efficient fuel burn for the 3.5-liter EcoBoost V-6 engine, delivering better drive cycle fuel economy and lower emissions
“¢ The 3.5-liter EcoBoost engine, the first V-6 direct-injection twin-turbocharged engine produced in North America, is the first in a wave of EcoBoost engines coming from Ford as part of a strategy to bring affordable fuel efficiency improvements to millions
CONTEXT / BACKGROUND:
By 2013, 90 percent of Ford’s North American lineup will be available with EcoBoost engine technology, which is one of Ford’s key initiatives to deliver significant advancements in fuel economy without sacrificing the performance customers want. Ford engineers used virtual tools and know-how to perfect the combustion system of the 3.5-liter EcoBoost V-6 engine in order to handle a wider range of operating conditions and pressures, and still deliver V-8 power coupled with V-6 fuel economy.
“The combustion system of the EcoBoost engine has to operate in a wide range of conditions and pressures, and that operation has to be seamless to the customer. Our method uses every bit of fuel, which improves fuel economy, and good mixing means you have good combustion, which means less pollutants.”
““ Jianwen Yi,
Ford EcoBoost Technical Leader
“Using our CAE (computer-aided engineering) tools and virtual engine, we were able to completely prove out the system. That’s a huge efficiency and time saving. From a research perspective, we’ve never been able to get that level of validation done so early.”
““ Craig Stephens,
Ford EcoBoost Powertrain Control System Manager
Ford’s combustion team is presenting several papers at the SAE International’s 2009 World Congress April 20-23 on some of the challenges overcome to make the combustion system of the 3.5-liter EcoBoost engine operate efficiently at cold start or top speed. Pressure, for example, can reach up to 2,175 PSI (pounds per square inch) in the EcoBoost combustion system, where a normal port fuel injection system typically ranges up to about 65 PSI.
To help account for this fluctuation, the EcoBoost engine’s injectors are fed fuel from a rail connected to a cam-driven high-pressure pump. At cold start, when there is virtually no pressure in the system, fuel is sprayed near the spark plug to provide a rich mixture that can be quickly burned so the engine starts easily. Once the engine starts, the six holes in the injectors spray the fuel in a pattern to help create what’s known as a homogeneous charge, where the fuel and the air from the intake are properly mixed and balanced for the most-efficient combustion.
When the engine is at speed, the fuel injectors dispense a “cloud” of fuel vapor that is optimized for quick and efficient burning.
Because the fuel is directly introduced into the combustion, there is no wall wetting, port saturation or droplets that might combine, which can take more energy and time to burn.
Understanding the physics of the fuel injection, atomization, fuel-air mixing and combustion processes is the key to EcoBoost’s optimized combustion system.
Extensive virtual modeling was used to cut down on the time needed to develop the actual hardware. Using computer-aided engineering and virtual tools, the 3.5-liter EcoBoost’s fuel injector, for example, went through 22 iterations on paper, but required only two hardware prototypes.