What Is EGR
EGR stands for Exhaust Gas Recirculation. It is a system that pipes exhaust gasses form the exhaust system back into the intake of the engine. The amount of exhaust gasses returning to the intake are usually regulated by a computer (ECU) controlled EGR valve. The purpose of EGR is to lower the temperature of the combustion gasses inside the engine by displacing some of the air/fuel mixture with inert exhaust gasses. This reduces the amount pressure produced by the combustion of air and fuel, resulting in a lower combustion temperature. Nitrous Oxides (NOx) are produced when the combustion temperature exceed 1200°C and create large quantities above 1700°C. Normal combustion temperatures can reach 2050°C in a diesel engine and 2750°C in a petrol engine. By lowering the combustion temperature with EGR, the amount of NOx produced is dramatically reduced. NOx is a gas that creates smog and acid rain.
What Is A DPF
DPF stands for Diesel Particulate Filter. It fits into to exhaust system of a modern diesel and from the outside looks similar to a muffler. The exhaust gasses, especially on diesels, are partly made up of particulate matter. Particulate matter is carbon soot and ash, the solid residue from the combustion process. The DPF has a honeycomb structure that is designed to filter out the larger particulates to prevent them being exhausted into the atmosphere. When the DPF gets full, the vehicles engine management system goes through a regeneration cycle where it burns off the the soot and ash in the filter.
What Goes Wrong
The particulate matter also gets fed back into the engine through the ERG system. Over time this clogs up the pipes, cooler, EGR valve and intake manifold of the engine causing poor running and idle of the engine.
In the case of the DPF the vehicle need to travel at motorway speeds for a certain length of time, usually 20 minutes or more, for it to complete a regeneration cycle. In stop start traffic this does not happen, the DPF gets blocked over time until it cannot be cleaned by the regeneration process. When the DPF becomes too restricted the ECU will turn on the DPF warning light on. The vehicle will run badly with increased fuel consumption and eventually turn the check engine light on as well. In some cases it is possible to do a forced regeneration in the workshop. This does not alway work if the DPF is too blocked.
Ultra Sonic Cleaning
There are various ways to restore the EGR system and DPF back to origional condition. The quickest but most expensive is to replace with new part. There are chemical treatment that have varying degrees of success, acid bathing and steam cleaning are also used. Chemical cleaning usually does a poor job. Acid bathing cannot be successfully used on ERG coolers and DPF's. Waterblasting damages the internal structure of the DPF honey comb. The only successful way that is non damaging and will bring the system back origional conditon, without new parts, is to use ultra sonic cleaning. At Khandallah Garage this is the process we use. It is effective and cost efficient process that will restore the system back origional condition. Please contact us for more infomation and pricing.
Low Ash Oil
Regularly changing the engine oil with a low ash oil is a regime all modern diesels should be following. Over time the oil gets diluted with fuel and drawn through the emission control system. It gets burnt in the combustion proccess and resulting particuate matter clogs the EGR and DPF system. Clean undiluted low ash oil reduces the amount soot and ash produced by the engine, greatly extending the service life of the EGR and DPF. Not regularly changing the oil with a low ash oil is a false economy. DPF removal is also not an option, the DPF is an intergral part of the system, all that will be achieved is causing the check engine light to stay on.