Great service businesses understand the value they can be to their customers when they can offer guidance and advice when servicing different parts found on a truck. Just like the radiator specialist being asked about overheating engines or premature radiator failure, the Diesel Particulate Filter (DPF) cleaning company will inevitably be asked about the exhaust system of a diesel engine. Your team must be educated about diesel emissions so they can offer that value added to your customers. Not every occasion a DPF is sent in for a cleaning will it be necessary to offer your guidance, but when the time does arise you will want your team to be prepared.
By being able to speak intelligently about the diesel exhaust system, your people can be a resource for your customers. In some businesses, the technician cleaning the diesel particulate filters is one of the least experienced people in your shop. To help them better understand the process, let’s do a simple review of how the diesel engine operates and the components that control and or create the exhaust. Understanding that the diesel particulate filter is just a trash can and only catches what comes down the exhaust pipe is the first step in understanding the process.
Understanding the Process
Let’s start at the beginning to help better understand the process. A simple review of how the diesel engine operates and the components that control and or create the exhaust will allow your entry level technicians to grasp the basic concepts. The 4-cycles of a 4-cycle diesel engine are intake, compression, power and exhaust. As the piston moves during each stroke, it turns the crankshaft. Air is drawn through the intake valve of an engine on the down stroke of the piston (1st cycle), next that air is compressed by the upstroke of the piston at a very high compression ratio to cause the heat needed to combust diesel fuel (2nd cycle). Near the very end of the compression cycle fuel is injected (the timing of the fuel injection is controlled electronically on all engines with DPFs) into the cylinder, combustion occurs (power) and pushes the piston down (3rd cycle). The exhaust stroke (4th cycle) is the final phase, the piston moves upwards, squeezing out the gasses that were created during the combustion stroke through the exhaust valve and into the exhaust manifold. The exhaust in the exhaust manifold enters the turbo which is bolted to the exhaust manifold. At the same time a precisely measured amount of exhaust gas is recirculated through the exhaust gas recirculation cooler which is mixed with fresh air from the charge air cooler, and the process of injecting air into the engine continues. This entire process happens anywhere from 800 to 2,000 times per minute depending on the Revolutions Per Minute of the engine so the flow of exhaust is constant.
Note: On a gasoline powered 4-cycle engine an air/fuel mixture is drawn in during the first cycle, it is compressed at a much lower ratio during the second cycle and then a spark plug ignites the air fuel mixture at the beginning of the third cycle to produce the power stroke.
By understanding the diesel engine’s process of creating exhaust, we can see the components that play a part in creating and controlling the exhaust. There is the turbo charger that is powered exhaust gas flow and heat which sends fresh outside air into the charge air cooler, the cooled air from the charge air cooler is mixed with recirculated exhaust gas which has been cooled in the EGR cooler. The fresh air and recirculated exhaust gas are blended by an EGR Valve. Looking at the drawing below, you can see how the air and exhaust are routed in a diesel engine.
There are certain parts which can malfunction and affect the diesel particulate filter. If fuel injector timing is not correct, if the injector malfunctions and does not atomize the fuel or leaks into the combustion chamber too early or too late it can cause incomplete combustion that results in white or black smoke. A leaking intake or exhaust valve will also cause a fuel rich burn sending unburnt fuel into the exhaust system, making the exhaust almost moist. This causes a problem with the diesel particulate filter because it is not designed to catch this type of mixture in the exhaust. Remember the DPF was designed to catch soot and particles produced in a properly operating combustion chamber of the engine. Along with the soot produced by the fuel, there is a certain amount of ash that is produced from the oil that lubricates the engine parts. In the last issue of this magazine, we talked about the importance of using the newest oils that were designed for reducing ash in the exhaust stream.
If an EGR Cooler develops a leak, the coolant enters the engine exhaust through the EGR valve and is exhausted from the engine into the exhaust stream thus producing a different type of ash which will prematurely clog the diesel particulate filter.
If a charge air cooler leaks beyond the manufacturer’s specifications it can cause the following issues:
- Increased fuel consumption
- Low engine power
- Excessive soot in the oil
- An increase in DPF regenerations
- Premature piston, ring and valve failure
- Elevated coolant temperature
- Frequent costly repairs of components like turbo and exhaust manifolds
There are a couple of interesting side effects caused by a leaking charge air cooler. If you look at the list you will see excessive soot in the oil and increased DPF regenerations, which means the DPF is getting plugged and premature wear of the turbo.
Lastly, any of these components can cause excessive strain on the turbocharger of a diesel engine. The turbocharger is receiving the exhaust heat in order to turn the turbine that produces the boost of the fresh air that is being circulated through the charge air cooler and finally into the engine. If any of the previous malfunctions occur which include fuel injectors, EGR coolers and charge air coolers, the diesel particulate filter can prematurely plug leading to excessive back pressure on the turbo. If the exhaust gas cannot flow freely through the turbo and out the exhaust system, the turbocharger operates at temperatures higher than what it was designed for, which can lead to premature failure.
Can a diesel particulate filter cause a turbo charger failure?
If the diesel particulate filter is blocked and passive regeneration does not clean the filter or frequent regeneration starts to occur this is an indication the turbocharger is having a greater amount of heat and back pressure placed on it. The free flow of exhaust needs to happen to prevent the heat build up which can cause the lubricating oil in the turbo to carbonize and clog the oiling system. If the oil carbonizes and blocks the lubrication then this is the beginning of the end for the turbo charger as the bearings will start to suffer.
As a diesel particulate filter service business, you must educate your customers and express the importance of having a preventive maintenance program that establishes regular cleaning cycles based on miles driven or time operated. This type of maintenance can be saving your customer’s turbo chargers and charge air cooler cleanings. When turbochargers fail they may spew oil into the charge air cooler thus requiring additional service for the charge air cooler. Regular pressure tests of charge air coolers is also advisable as leaking charge airs can also have an effect on all of the related components.
Hopefully your technicians can achieve a basic level of diesel engine emissions knowledge, so they can better understand the importance of clean filters and better communication with the customer.
This article was originally published in the November/December 2021 issue of The Cooling Journal.