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Aerodynamics 101

Aero U

How Fuel is Consumed in a Heavy Duty Truck Engine

The contribution to fuel burn can be divided into five elements:

  • Aerodynamic Drag
  • Power Train Losses
  • Grade Changes
  • Rolling Resistance
  • Accessory Losses

At highway speed, aerodynamic drag accounts for over 65% of the fuel consumed by a tractor-trailer.

The table below illustrates the contributions to fuel burn at various speeds, assuming a zero grade, properly inflated tires and that the internal power train losses can be modeled as a constant relative to vehicle speed.

Vehicle Speed Aerodynamic Rolling & Accessories
20 mph (32 kph) 28% 72%
33 mph (53 kph) 33% 67%
40 mph (64 kph) 36% 64%
50 mph (80 kph) 50% 50%
60 mph (96 kph) 62% 38%
65 mph (105 kph) 67% 33%
70 mph (113 kph) 70% 30%

 

Since aerodynamic drag is but one source of fuel consumption, reducing aerodynamic drag by 20% will not result in a 20% reduction in overall fuel consumption. Rather, it will be 20% multiplied by the percentage contribution of aerodynamic effects at that particular speed.

For example, a 20% reduction of aerodynamic drag via the use of aerodynamic devices would have an overall effect of reducing fuel consumption by approximately 9.4% at 50 miles per hour.

The fuel savings rise as speed increases, yielding a maximum value of approximately 14.4% at 75 miles per hour.

Tractor-Trailer Aerodynamics

A truck in motion encounters resistance drag from the air flowing at and around it. This drag is made up of pressure drag and skin friction drag.

The oncoming airflow pushes against the front of the tractor, creating a high-pressure region, just as it does on the wheels and the front of the semi-trailer.

The truck moving forward in the airflow creates a low-pressure region behind the tractor and the semi-trailer: these areas create aerodynamic drag that pulls the vehicle backwards, increasing fuel consumption and strain on the engine and drive train.

TrailerTail® by STEMCO maximizes the return on other aerodynamics investments by minimizing the low-pressure vacuum at the rear of the trailer.

The most fuel efficient and profitable trucking fleets employ aerodynamic trucks that minimize the gap between the truck and trailer, install side skirting to prevent air from hitting the trailer’s rear axles and TrailerTail® technology to streamline airflow at the rear of the vehicle.

How TrailerTail® by STEMCO Works

TrailerTail® by STEMCO reduces vehicle fuel consumption by reducing the low-pressure vacuum that occurs directly behind the tractor-trailer.

The large low-pressure area at the back of the trailer acts as vacuum, causing drag and a turbulent vortex of unstable airflow. TrailerTail® technology diminishes the low-pressure area, reducing drag and streamlining the airflow to improve vehicle stability and fuel efficiency.

TrailerTail® fuel savings complement other aerodynamic technologies. A TrailerTail® reduces aerodynamic drag by over 12% equating to over 5% fuel efficiency improvement at 65 mph and over 12% fuel efficiency improvement when combined with STEMCO’s side skirts and other minor trailer modifications.

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