To meet the latest stringent emissions regulations, a lot of Yanmar TNV water-cooled diesels are having to be fitted with DPF systems. But what are DPF’s?
DPF’s are diesel particulate filters and are fitted to most medium to large Yanmar TNV engines and are basically a large extra filter bolted on to the engine and the exhaust gases that are emitted after the combustion process pass through it before being released into the air. It’s not just a silencer though, it’s a complicated piece of equipment. Diesel exhaust fumes contain particulates which are harmful to health and it’s the job of the Yanmar TNV engine DPF to capture these before they enter the atmosphere. Inside of the Yanmar TNV engine DPF is a silicon carbide filter which the exhaust gas passes through, collecting the small particulate that is harmful to health and is that efficient it can capture up to 99% of them. As with all filters though, the Yanmar TNV engine DPF can become blocked and therefore affect the efficiency of the engine but you can’t keep changing the Yanmar DPF every couple of hours, especially not at over £600 per filter!!
This is where the clever bit happens as the Yanmar TNV engine DPF re-generates to clean itself. There are two sensors on the DPF housing, one on the inlet side and one on the outlet side measuring the pressures in the two areas on the filter. These two sensors send information to the Yanmar ECU, when the DPF is clean and working the two pressures are reasonably balanced and the ECU doesn’t have to do anything. However, as the DPF becomes blocked the inlet pressure rises as it cannot push the gas through the restricted silicon carbide and the outlet pressure decreases as the exhaust gas volume decreases. The Yanmar ECU senses this new pressure differentiation and therefore needs to raise the temperature inside of the Yanmar TNV engine DPF to over 550 degrees centigrade to burn off this particulate blockage. It does this by sending diesel to an injection unit on the Yanmar TNV DPF which ignites inside the filter thus burning the soot off. As soon as the two sensors recognise that the pressure is becoming balanced it shuts of the fuel to the Yanmar TNV engine DPF injector and normal operation is resumed.
This happens all the time with no input from the machine operator, the only thing they notice is that there might be a yellow re-generation light illuminate on the dash and the Yanmar ECU will increase the engine revs if idling to ensure the temperature within the Yanmar TNV engine DPF remains above the critical 550 degrees centigrade.
Eventually the silicon carbide filter inside the Yanmar TNV DPF won’t re-generate itself enough to clean itself and therefore has to be replaced or sent away for specialist cleaning process.