How is the Diesel Oxidation Catalyst different / better than a DPF system? I was told by Mahindra dealer that a DPF system cost $6k to replace and that it had a finite life. Does DOC last forever? Not having a high heat generating DPF sounds good to me but why does everyone else use it? Maybe I'm missing something?
Google search is great tool... lol.
DOC is a catalytic converter. The exhaust gas passes through a material which oxidizes/breaks down the environmentally "harmful" stuff.
"The diesel oxidation catalyst is designed to oxidize carbon monoxide, gas phase hydrocarbons, and the SOF fraction of diesel particulate matter to CO2 and H2O"
A DPF is a more extensive breakdown system. It usually has a DOC, then a DPF. Some systems also use Diesel Exhaust Fluid (DEF), in addition, which is yet another addition, spraying that fluid the exhaust to further break down the "harmful" particles.
" Exhaust gas passes through the DOC and then into the DPF where Pariculate Matter is collected on the walls of the DPF. The PM collected is then oxidized to remove it from the DPF. This is known as regeneration. When operating conditions maintain sufficient exhaust temperatures, the DPF is continually self-regenerating. This is known as passive regeneration and results in clean exhaust out of the tailpipe. On very infrequent occasions, an active self-regeneration is required to remove a build-up of PM in the DPF, due to insufficient exhaust temperatures. Exhaust temperatures are raised by injecting a small amount of fuel upstream; The resulting chemical reaction over the DOC raises exhaust gas temperatures high enough to oxidize the PM from the filter."
To the best of my knowledge, the Mahindra Common Rail Diesel engine was designed with the modern electronic components to properly manage and optimize fuel used in the engine, this results in minimal excess waste, which the DOC can take care of. Specific components are things like the Bosch CB18 fuel pump which has a mechanic side to bring fuel form the tank to the pump, then an electronically controlled metering system (which receives input from multiple sensors) that limits the amount of fuel in the high pressure side and up to the fuel rail and injectors. Things like the engine speed sensor, rail pressure sensor, etc all help the ECU to fine tune the perfect amount of fuel to get to engine, but not excess. Then things like the EGR system help eliminate excess pollutants out of the exhaust before the DOC. So little to no unburned fuel and pollutants out the exhaust.
Realistically, this is all just making the engine and fueling efficient and there is no excess. That's why these tractors arent puffing black smoke like all of the old stuff. Old models did everything mechanically, where it would only grossly calibrate how much fuel was being put in to the engine, wasting more and polluting more.
It's essentially like the transition from carburetors to fuel injection. A computer monitoring and managing everything to make it as efficient as possible. Sure it's a little more "complicated" but I prefer to say complex. and yea, it can be a pain when sensors arent working or there isn't good ECU software support (which Mahindra does struggle with here in the US). But all things aside, it's actually a decent design. and it can have it's benefits.
I guess it's kind of like pick your poison, an engine with less electronics to make fuel use efficient will need the more extensive exhaust oxidation system to meet emission requirements. The other side is the use more electronics to make the engine more efficient which requires less exhaust oxidation treatment.
-Haas
