Diesel Timing

[nspec]

Many diesels have 'unit injectors'. The pump and injector are combined into one unit for each cylinder. There is a lift pump on the engine to deliver fuel to the unit injectors. An overhead camshaft then charges each injector with high pressure fuel, and finally the actual fuel charge is sprayed into the combustion chamber by an electrical solenoid telling the nozzle when to open and close. Another take on this is Caterpillar's 'HEUI' system, where instead of the camshaft driving the unit injectors, engine lube oil passes through another system which somehow runs the injector and the injector itself pressurizes the fuel charge before the electronics again tell it to fire. (Hydraulically controlled Electronic Unit Injector)

 

[nspec]

Also, if I'm not mistaken, part of the formula used by the electronics to control when to fire each injector is based on a crankshaft position sensor. This is at the most basic level. Newer engines also take engine load, charge air temperature, individual cylinder temperature, turbo speed, etc, etc.... into account when timing the injectors to allow for the best performance and eliminate smoke. The timing thus varies continuously to a certain degree.

 

[MHarryE]

The more modern and efficient engines use a common rail. An electronically controlled fuel pump feeds a common rail (distribution manifold) where pressures can be as high as 30,000 psi. This higher pressure allows the injectors to break the fuel into smaller droplets for more efficient combustion. The newest injectors use piezoelectric valves that allow multiple injection events. The most advanced shot on an engine with which I have worked was 45ｰ BTC. These new systems provide improved efficiency and tremendous torque backup. For example, our 7730 Deere uses .412 pounds per HP-hr while a 4020, common when I graduated, uses .486 pounds per HP-hr or nearly 20% improvement. The difference is easy to see - the 4020 had a cloud of black smoke from the exhaust under high load while the 7730 stays clean. Black smoke = unburned fuel because they overfueled it to get more power. When you hear about people turning up the pump on the older style (shouldn't say that - my Kubota L5740 uses the older style pump) they are actually increasing the overfueling to make sure all the oxygen gets used up to produce power but its not very good for efficiency.