Perspective: Mack Pioneer Wedge Cuts Drag, Widens Cab
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Earlier this year, Mack Trucks introduced the Pioneer, its latest entry into the truck market and one designed, per Stephen Roy, the company’s president, to capture a greater share of the longhaul Class 8 market.
One major key to the new model’s potential success is its combination of advanced aerodynamic design and driver ergonomics in the form of a wedge shape. This shape allows sleek, smooth flow of air over the tractor from the relatively narrow grille to the fairings at the rear of the cab, keeping the airflow smoothly attached to the cab’s sheet metal, reducing aerodynamic drag.
The rear cab fairings complete the wedge, thus guiding the air smoothly around the wider trailer. One very important byproduct of the design is more cab width, allowing wider seats with armrests on either side. With two armrests, the driver’s entire body — including his or her arms — rides on the air seat rather than the cab itself when hitting larger bumps. A wider seat is obviously going to please drivers with a roomier feeling.
Another area where the new vehicle shines is in the complex network of vents designed to cool all the components inside the engine compartment, including the power steering system, and even the headlamps. An aero tractor forms an envelope of air around itself that moves forward like two people inside a horse costume. Thus, the basic shape provides too little cooling for all the under-cab components, especially vulnerable items like hoses and electricals.
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Providing the cooling needed under the hood and headlights hits a perfect equilibrium. Any vent in the hood or cab tends to generate turbulence, thus interfering with perfect attachment of the air flowing around the vehicle and increasing drag. So, the job of protecting all the electronics and mechanicals with airflow becomes a scientific balancing act.
“All the front-end openings, including the hood and front bezel inlets, are designed to facilitate the entry of ambient air into the underhood area for quicker cooling of the components located there,” said Lukas Yates, Mack’s chief designer. “We optimized the (top of hood) vent locations and size with CFD (computational fluid dynamics) simulations to see what would net us the most airflow into the hood without disturbing the overall aerodynamics of the truck.”
Yates explained that the hood surfaces in front of the vent openings were tuned to get the best airflow characteristics into the intakes.
“The size and location of these openings are determined after extensive CFD simulations to achieve maximum cooling efficiency (from all the openings in the front end) without penalizing the aero targets of the new Pioneer,” he added. “The exit vents positioned behind the side air intake grilles are intended to allow hot air from the underhood to escape.”
One area where the new vehicle shines is in the complex network of vents designed to cool all the components inside the engine compartment. (Mack Trucks)
Yates further explained that these features are engineered to enhance the convection within the underhood and to lower overall temperatures of various components — including the oil pan, turbo, exhaust gas recirculation system, various electronic control units and electrical componentry — across different operating conditions.
The grille itself is another challenge. The radiator must handle all the heat from the engine, including much of the heat that gets into the oil via the oil cooler, as well as all the heat from hot exhaust cooled in the EGR cooler. The transmission doesn’t need a separate source of cooling air as the mDrive transmission has a substantial trans fluid/coolant heat exchanger. But, all this heat ends up in the radiator.
As if that were not enough heat to remove, the charge air cooler must remove the substantial amount of heat generated as intake air passes through the turbo compressor, which normally heats that air to well over 300 degrees Fahrenheit. The cooler the air after it passes through the charge cooler, the greater the volume of air supplied to the engine. Cooler intake air also significantly increases the engine’s efficiency and decreases waste heat.
In this connection, Yates said the front grille’s size, location and configuration are crucial for managing the airflow into the engine compartment, which directly affects the thermal management of the vehicle.
“Proper airflow is essential for maintaining optimal engine temperatures, which in turn influences engine efficiency, fuel savings, reliability and emissions,” he explained. “These factors are critical as they align with stringent requirements set by powertrain and engineering teams.”
The front grille’s size, location and configuration are crucial for managing the airflow into the engine compartment. (Mack Trucks)
To achieve these objectives, Yates said, extensive simulations and testing are conducted.
Finite element analysis and computational fluid dynamics are employed to model and predict the thermal and fluid dynamics behavior.
“These simulations help in designing a cooling package that includes the front grille, side air intakes and air cleaner system, as well as selecting appropriate heat exchangers like the radiator, charge air cooler and air conditioner condenser,” he said. “The goal is to meet specific fuel economy and emission targets.”
Another challenge for designers is the engine air intake system since the air must flow freely, but water from a heavy rain must be excluded. “The air intake system’s design is influenced by a pressure drop requirement set by the powertrain team and also a reliability target for the air cleaner filter in the air cleaner,” Yates said.
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This requirement is crucial because the pressure drop across the air intake system affects the engine’s ability to draw in air efficiently, which in turn impacts fuel economy and overall vehicle efficiency.
To meet these targets, the size and location of the side air intakes are meticulously optimized, balancing the need to minimize pressure drop with other considerations, such as reducing water ingestion during heavy rain, Yates noted. Water ingestion can adversely affect the air filter, potentially leading to reduced engine performance or damage.
“Additionally, the design includes ribs on the hood reinforcements located behind the side intake grilles. These ribs serve a dual purpose: They help block heavy water particles from entering the air cleaner system while allowing fresh air to pass through,” he said, noting that overall, the design of the air intake system involved careful consideration of various factors to ensure optimal engine performance, fuel efficiency and reliability under various operating conditions.
One final boon to the Pioneer’s on-highway fuel economy is an advanced powertrain, said Blake Routh, Mack’s senior product manager for highway trucks.
“With the new Mack Pioneer, Mack is proud to offer the new Dynamic Overdrive powertrain package. Dynamic Overdrive pairs the MP13 High Efficiency engine with Mack’s intelligent transmission shifting software to optimize fuel efficiency for the customer, without compromising power,” he said.
Routh explained that the Dynamic Overdrive is best paired with a 2.15 rear axle ratio to optimize downspeeding, which leads to better fuel economy. Mack’s updated powertrain in the Pioneer delivers 3% better fuel economy than the prior model, in part because of optimizing combustion due to hardware designs such as its 7-wave piston.
The 7-wave piston works in concert with a 7-hole injector. This means finer fuel sprays that more quickly mix with air and enhanced combustion chamber turbulence. This allows better combustion for lower emissions and better fuel economy.
This super downsped engine, which includes a turbo-compounding turbine that follows the turbocharger, combined with a super-fast axle, is a concept originating in the mind of owner-operator Joel Morrow and perfected by the company. The 2.15:1 axle ratio allows a cruise RPM of about 960 (still above the 900 RPM torque peak) under level road conditions, but the transmission is programmed to downshift to the direct 11th gear immediately when more power is needed for hill climbing or acceleration.
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