The traditional diesel engine consists of a mechanically governed fuel injection pump and fuel injectors to provide atomised fuel to be burnt in the combustion process therefore turning the crankshaft. The fuel injection pump was mechanically driven from the engine timing gears which pressurised the fuel which caused the injections to ‘crack off’ at a certain pressure. As you can imagine it is a fairly inaccurate method of delivering fuel at a precise moment, gear backlash, worn fuel injection pump, weak injector springs can all add to in-precise injection causing an inefficient combustion process leading to unburnt fuel being emitted in the exhaust process.
With the tightening of emission regulations the only way to meet the criteria, especially with larger engines, was to control the process electronically. The Yanmar common rail system utilises a Yanmar designed electronic control of fuel injection which utilises an ECU to provide total intelligent engine control. Instead of the traditional fuel injection pump Yanmar have used a high-pressure pump to generate fuel pressure stored in a common rail to which all the Yanmar injectors are linked to. These Yanmar injectors are now electronically controlled, when the Yanmar ECU instructs the injector to open it allows the high-pressure fuel through the injector, atomising it into the combustion chamber where it is burnt. Instead of the one ‘squirt’ in a mechanically governed fuel injector, the Yanmar electronic injector can operate up to 5 times in 1/1000th second intervals in a multi-stage injection process therefore reducing nitrogen oxide and particulate matter. The Yanmar ECU takes real time information from sensors such as coolant temperature, fuel pressure, camshaft position, crankshaft position, inlet air temperature, throttle position to precisely work out how much fuel is required for each injector to atomise into the combustion chamber, thus reducing emissions.
Coupled with the Yanmar electronics, Yanmar utilise an Exhaust Gas Recirculation System (EGR) to recirculate some of the exhaust back into the air intake system. Connected to the exhaust manifold, the Yanmar EGR system takes some of the exhaust gas and put’s it through a cooler to reduce the temperature and when the Yanmar ECU instructs the Yanmar EGR valve to open it lets the cooled exhaust gases back into the combustion chamber with fresh air to go through the combustion process again. This reduces the nitrogen oxide emission by controlling the oxygen concentration in the combustion chamber and therefore reducing the combustion temperature.
The process is finally finished by putting the exhaust gases through a Yanmar DPF system to take particular matter out before the exhaust gases are emitted into the air. This Yanmar DPF system consists of a diesel particulate filter (DPF) and diesel oxidation catalyst (DOC) to trap particulate matter which is then burnt off by introducing a small amount of fuel into the system therefore cleaning the filter. This Yanmar DPF system is again controlled by the Yanmar ECU which detects the amount of blockage in the filter and starts a regeneration process to clean it.
Now this might explain to you why when you start a cold diesel engine or keep your foot on the throttle when loading the engine you don’t get clouds of black smoke coming out of the exhaust like you used to in the ‘old days’. These complex Yanmar electronic systems control all facets of the engine, you might be pressing the throttle pedal but it’s the Yanmar ECU that’s controlling the engine!!!!