by Jim Kerr
Sometimes you just need a vehicle for work. Power to haul a heavy load is mandatory, but so is quiet operation, durability, performance and in this day and age, fuel economy. Diesel engines are attracting more attention all the time as gasoline prices rise. Ford’s 6.0 Litre Power Stroke diesel engine, with its 325 horsepower and 560 ft lbs torque is one of the newer diesels to enter the market. While the Power Stroke name has been around for a while, the 6.0 litre engine is all new and incorporates a few unique features.
This is an electronically controlled direct injection diesel engine. Direct injection describes the fuel being injected directly into the engine cylinder instead of a pre-combustion chamber style external to the cylinder used on some diesel engines. Three systems on this engine combine to deliver fuel into the engine.
The computer system with all its sensors is the brain of the operation. The computer controls the timing of fuel injection, the duration of the injection pulse and the pattern of injection pulses. The Power Stroke engine utilises pilot injection. This means that under many operating conditions, the computer actually triggers each injector twice for every power stroke. Pilot injection sprays a small amount of fuel into the engine to start the combustion process followed by the main injection pulse to produce the power. The pilot pulse reduces vibrations inside the cylinder that we hear as that typical diesel rattling noise, so engine operation is much quieter.
The second system is the fuel system. Diesel fuel is pulled from the fuel tank by an electric pump in the fuel conditioning module located on driver’s side frame rail. The module contains the primary fuel filter (10 micron), water separator, water in fuel sensor, fuel heater and a fuel drain. From the fuel conditioning module, the fuel passes though an even finer 4 micron fuel filter before passing into the heads and into each injector. Then the fuel waits for oil pressure to do its work.
Ford’s 6.0 litre Power Stroke diesel engine. Click image to enlarge
The engine oil system is the final major part of the 6.0 litre’s injection operation. Oil is pumped from the pan into an oil cooler located in the valley area between the cylinder banks. The oil then flows into the filter on top of the engine. From there, oil is used to lubricate all moving parts but about a litre of oil also flows into an internal reservoir located under the oil cooler. Oil from the reservoir supplies a high pressure oil pump driven by gears from the crankshaft and camshaft at the back of the engine. This oil pump delivers up to 4000 psi oil pressure to high pressure oil rails on each cylinder head. There, the high pressure oil is ready to operate the injector.
Two electro-magnetic coils inside each fuel injector are controlled by the computer to allow engine oil into the injector or to dump the oil already there into the oil pan. The computer pulses the inlet coil for 800 milliseconds, moving a small spool valve sideways about 0.017 of an inch. An opening in the spool valve allows oil into the injector onto the top of a piston. The piston is pushed down by the oil pressure, which moves a plunger down that is seven times smaller than the piston. This plunger pressurises the fuel, forcing it out past the injector pintle needle valve and into the engine. When the required fuel has been injected, the computer now pulses the close coil and the spool valve moves back, stopping the fuel injection.
Because there is a 7 to 1 ratio in area between the piston and plunger, 4000 psi oil pressure is increased up to 28,000 psi diesel fuel injection pressure for precise fuel control and economy, and maximum power with low emissions. Other manufacturers use direct electronic control of fuel to inject the fuel. Ford controls oil pressure to create the injection pressure. By operating with low fuel pressures (about 60 psi) they avoid erosion problems that can occur with high fuel pressures and dirty fuel. One drawback is that oil used in the Power Stroke engine must be the correct type or it may foam as it passes through the injector, causing rough running and hard starting.
There are many other features of the Power Stroke engine that enable its outstanding performance. These include a variable vane turbocharger, an air to air intercooler and a four valve per cylinder head design. A five speed automatic transmission behind this engine helps performance too.
Ford’s 6.0 litre Power Stroke engine is a modern diesel that offers the clean power and performance we seek in a work vehicle with sophistication that allows owners to drive a diesel with the same comfort level as a gasoline engine. Diesels sure have come a long way from their dirty, noisy, smokey beginnings.