Improved atomization is just part of the equation. High operating pressure combined with powerful engine management electronics allow precisely manipulating the shape and location of the fuel charge in the chamber. This is accomplished by making multiple injections in the combustion chamber every intake cycle, and varying fuel pressure anywhere between 200-2,200 psi. In other words, direct-injection fuel systems have the ability to administer fuel in multiple spurts at any point between TDC on the intake stroke and TDC on the compression stroke. A standard port fuel injection system, on the other hand, can only introduce fuel into the chamber when the intake valve is open, which is dependent on the profile of the cam lobes. "By injecting fuel directly into the combustion chamber and under high pressure, the fuel can be directed to exactly where we want it to be for a given combustion cycle," Hinds adds.
So how exactly does this translate into improved fuel economy and power? It's all in direct-injection's ability to separate the combustion chamber into separate zones. At idle and under part-throttle, the fuel charge is stratified, which means that it's concentrated near the spark plug. Conversely, the layer of air surrounding this zone is extremely lean. The result is an air/fuel mixture that's lean overall, yet stoichiometrically ideal near the spark plug. Under part-throttle operation and at idle, this reduces fuel consumption by up to 40 percent. As throttle input and load increases, a direct-injection system transitions to a homogeneous fuel charge, in which fuel is dispersed evenly throughout the entire combustion chamber. In addition to reducing emissions during cold starts by warming up the catalytic converters more quickly, the leaner overall air/fuel mixture boosts torque by about five percent. "The EcoBoost engine is constantly controlling the rail pressure to a target level based on what the customer is demanding from the engine," explains Todd Rumpsa, EcoBoost calibration supervisor. "As the driver increases demands on the engine, higher rail pressures maintain optimized combustion performance by delivering the best atomization of fuel and precise injection duration." For extra peace of mind, the Bosch engine management system used in the EcoBoost can retard timing up to 20 degrees on the fly, which negates the need for costlier forged rods and pistons.
Mounted in the cylinder heads...
Mounted in the cylinder heads directly between the intake valves, the EcoBoost's high-pressure injectors spray an ultra-fine mist of fuel through a six-hole nozzle. Unlike a carbureted or port fuel-injected motor, direct injection can still administer fuel even after the intake valves are closed. In order to handle the extra heat generated by the turbos, Inconel valves have been fitted to the heads.
Variable valve timing is accomplished...
Variable valve timing is accomplished on the EcoBoost through the use of phasers mounted to the front of the intake camshafts. The exhaust cams' valve events are fixed. To save space, Ford ditched the cam followers used on many OHC designs in favor of mechanical lifters that actuate the valves directly. Ford calls the system DAMB (Direct Acting Mechanical Buckets), and the tappets never require adjustment.
The Garrett GT15 turbos strapped...
The Garrett GT15 turbos strapped to the EcoBoost are small, which limits maximum power potential in the hands of hot rodders, but this arrangement increases exhaust velocity into the turbine at low rpm to minimize turbo lag. The insulating properties of the twin-wall manifolds help retain heat in the turbos to further enhance response. Note the twin fluid lines, one for oil and the other for coolant. The water-cooled turbo bearings eliminate the need to idle the engine after it has reached operating temperature, and reduce the potential of oil coking.
During WOT, the turbine wheels...
During WOT, the turbine wheels can reach speeds up to 170,000 rpm and temperatures up to 1,740 degrees F. As the turbos reach peak boost, electronically actuated internal wastegates bleed off exhaust gases before they reach the turbine wheels to limit boost pressure. Ford rates the life expectancy of the EcoBoost's turbos at 10 years and 150,000 miles.
Lifting off the throttle in...
Lifting off the throttle in a turbo motor creates a pressure spike in the intake tract. This shock can decelerate and potentially damage the turbine/compressor wheel and bearing. Anti-surge valves mounted between the intercooler and throttle body help relieve this pressure. Taking things one step further, instead of relying on vacuum pressure, Ford actuates the valves electronically. Consequently, Ford is able to open and close the anti-surge valves not only to relieve pressure spikes, but also to smooth out boost delivery and reduce the whistling noises often associated with turbos.
Since boost pressure masks...
Since boost pressure masks its displacement handicap, the EcoBoost's intake manifold features relatively short intake runners and reduced plenum volume to minimize turbo lag and improve hood clearance. A drive-by-wire throttle body is used in conjunction with electronically controlled wastegates to smooth out power delivery.