DIESEL EMISSIONS
Turbos, EGRs, & Charge Air Coolers: How Do They Affect DPFs?
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. Please refer to Diagram 1. 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
By: Mark Taylor
NARSA/IDEA Executive Director
mtaylor@narsa.org
Diagram 1 (courtesy: Detroit Diesel).
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
14 | THE COOLING JOURNAL | November/December 2021
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
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