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The PowerStroke Turbo Diesel is a 7.3L V8 engine made by Navistar. It is an option in the F-Series trucks.
The PowerStroke Turbo Diesel is one of the first to employ the HEUI system -- HEUI stands for Hydraulically actuated, Electronically controlled, Unit Injector, and it is the latest thing in diesel injection systems. It's only real downsides are it's reliance on sensors and computer hardware that other diesels may not have required, and the demands it places on an engine's lube oil. HEUI was developed by Caterpillar, but interestingly enough is currently only in use on engines manufactured by Navistar. It is unknow what kind of fee Cat obtains for the use of this technology, or if there is any fee at all.
One incarnation of Navistar's T444E is the 7.3L V8 direct injection turbo diesel that Ford calls the "PowerStroke" and markets in it's line of trucks. The T444E is also currently enjoying popularity in school bus and straight truck applications. Engines that utilize HEUI injectors are generally more powerful (they have flatter torque curves), pollute less, and use less fuel than comparable engines utilizing traditional mechanical (injector pump with high pressure injector lines and injector nozzles), or hydro-mechanical (cam activated unit injector) injection systems. While it can be argued that EUI (Electronic Unit Injector - cam activated) systems like the Cummins CELECT are just as good, HEUI systems have fewer mechanical parts, and "seem" simpler. Other non-HEUI diesels, for the most part, all must drop fuel injection pressure with a drop in engine rpm, possibly causing inefficiency around the engine's peak torque rpm.
Navistar's HEUI equipped engines utilize a swash plate
type oil pump to supply pressurized lube oil to oil "galleries" or
"rails" machined into their cylinder heads. Low pressure fuel is supplied
to the injectors through a fuel pump and fuel "rails" which are machined into
the heads much like the oil galleries. It is the high pressure lube oil from the oil
galleries that is called on to act as the hydraulic fluid used fire the fuel injectors.
This is in contrast to the high pressure shot of fuel or cam lobe action that has more
traditionally performed this function. A HEUI engine has no injector pump or high
pressure external fuel lines nor do they have an extra cam lobe/rocker arm per injector to
maintain. Once past the ECM, these engines are in fact relatively logical &
simple.
The HEUI engine is totally controlled by a computer, usually referred to as it's ECM, which basically acts as a very advanced electronic governor. The ECM utilizes an array of sensors present on the engine to determine things like barometric pressure, turbo boost pressure, oil gallery pressure, air temperature, etc. The ECM is free to vary the pressure, quantity, and timing of the injection cycle as it sees fit based on readings obtained from these sensors. It is because of this that these engines cannot be overfueled, never emit black smoke, and attain their highest fuel economy with the cruise control set, where there are no driver generated "interruptions". It is both safe and economical to allow these engines to "lug" right around peak torque RPM - quite a departure from traditional diesel driving habits where the driver would usually shift into a lower gear. The HEUI injection cycle works this way - the idle injectors fill with low pressure fuel obtained from the fuel rail. The ECM has read it's sensors and has determined the optimum injection duration (how much fuel to inject), the optimum injection pressure, and has controlled a check valve to bring oil in the oil gallery to the correct pressure needed to provide the desired injection pressure. The oil gallery pressure can be infinitely varied by the ECM to be between 500 & 3,000 PSI, making fuel injection pressures of up to 18,000 PSI a possibility.
When the ECM decides to fire an injector (it can occur anywhere from 10 degrees BTDC to 20 degrees ATDC) it opens a solenoid valve to let pressurized oil from the oil gallery into the injector, which causes the injector to begin injecting it's fuel. When enough fuel has been injected, the ECM shuts the solenoid valve, ending injection. The oil left in the injector is allowed back into the oil gallery, where it ultimately will return back to the oil pan through the check valve to be used again as either hydraulic fluid or lube oil.
It is easy to see that these engines are sensitive to the type, condition, and quantity of oil that is present in the sump. Low oil levels or oil of an incorrect viscosity or API grade can cause erratic drivability problems and strange fuel usage patterns. In some cases, the engine may not be able to run at all. The original "PowerStroke" engines that Ford sold in fact had some odd behavioral problems that were corrected by adding 2 additional quarts of lube oil and a new dipstick. It is also true that a malfunctioning HEUI injector can directly contaminate it's engine's lube oil with diesel fuel, and vice versa. While fuel contaminated lube oil has always been possible no matter what the injection system design, it is now invariably more possible for it to occur, and for obvious reasons other than an abnormal spray pattern or incomplete combustion.
Last modified: Thursday December 13, 2007 07:35 AM
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