Cooled EGR, internal EGR on Mack diesel engines
25 March 2002
Mack Trucks Inc. announced it will employ two distinct heavy-duty diesel engine strategies—one for highway vehicles and one for vocational vehicles—to meet the EPA emission requirements starting in October 2002. The new EPA 2002 certified engines will be known as the ASET family, which is an acronym for Application Specific Engine Technology.
All ASET engines rely on exhaust gas recirculation as the basis for reducing emissions. For all Mack engines ticketed for highway tractors, including the Vision by Mack and CH Series, the company will use cooled exhaust gas recirculation (C-EGR) technology. For those engines destined for vocational trucks (i.e., construction and refuse)—the new Granite Series, RD6, MR, LE, DM and RB models—internal exhaust gas recirculation (I-EGR) will be employed.
The Mack ASET technology for highway applications will be based on cooled exhaust gas recirculation in which a portion of gases leaving the engine are diverted from exhaust through a cooling system, and then remixed with air entering the engine for combustion. C-EGR allows for the best level of performance and emissions benefits in a “steady-state” operating environment, i.e., when the vehicle is operating at relatively consistent speed and load over a significant period of time. Modifications to the fuel system and software were the initial changes made to Mack engines in developing its C-EGR technology. An improved filtering medium was then added to the oil filtration system, along with a new oil pan that accommodates an additional seven quarts of oil that the C-EGR engines will require. The increased oil capacity of the new engines will allow to keep the existing oil change intervals.
Mack said the new highway engines feature a number of innovations developed specifically to accomplish C-EGR and deliver optimum performance. They include a new EGR valve, electronically controlled by the Mack V-MAC system, to regulate the recirculation of exhaust gases, and a Mack Venturi mixing valve that combines inlet air and cooled exhaust gas prior to introduction into the cylinder. A new variable geometry turbocharger provides the pressure necessary to drive the recirculated gases into the intake valve.
With the introduction of the ASET family, Mack will offer a new MaxiCruise 380/410 ASET C-EGR engine as part of its engine lineup.
The ASET engines for vocational applications will rely on internal exhaust gas recirculation (I-EGR). I-EGR accomplishes emissions reduction by having a percentage of exhaust gases remain in the cylinders of the engine from one combustion cycle to another, until the targeted emission levels are met. According to Mack, this approach provides a consistent level of emission benefits and performance in the varying environments in which vocational trucks operate. These trucks often perform in a stop-and-go manner over shorter distances, where operational hours are a more important concern than miles traveled.
Mack engine designers optimized the flow of exhaust gases through the system, in order to make it possible to retain a precise amount of gases in the cylinders for further combustion. That was accomplished through a new camshaft, advancements to the valve system, and precision machining of the exhaust ports to maximize aerodynamic flow.
The Mack ASET engine offerings include two brand-new products—Maxidyne 335 and 370 engines—with I-EGR technology.
Source: Mack Trucks