Heavy-Duty Truck Fuel Economy Testing & Evaluations
Automotive Engineering

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In addition to developing fuel economy improvement technology, truck fuel economy has been evaluated by Southwest Research Institute (SwRI) since 1973. The mild climate in San Antonio allows year round testing on public roadways and test tracks.

  • SAE Recommended Practices

    • SAE J1321 Joint TMC (Technology & Maintenance Council)/SAE Fuel Consumption Test Procedure Type II (1986 revision)
    • SAE J1321 SAE Fuel Consumption Test Procedure Type II (2012 revision)
    • Interim test method for verifying fuel-saving components for SmartWay™; modifications to SAE J1321
    • SAE J1376 Fuel Economy Measurement Test (Engineering Type) for Trucks and Buses
    • SAE J1526 Joint TMC/SAE Fuel Consumption In-Service Test Procedure Type III
  • TMC Recommended Practices

    • RP1102 In-service Fuel Consumption Test Procedure Type II
    • RP1103 In-service Fuel Consumption Test Procedure Type III
    • RP1109 Type IV Fuel Economy Test Procedure

SAE recommended practice J1321 specifically addresses the needs and operating conditions of long-haul truck fleets. SAE J1376 is the appropriate procedure for testing and evaluating fuel consumption during operating cycles representative of bus, pickup and delivery, and refuse operations. To compare one vehicle to another, the use of SAE J1526 is the preferred method.

image: Fuel economy evaluations on trucks such as these are routinely performed at test tracks and on public roads.

Fuel economy evaluations on trucks such as these are routinely performed at test tracks and on public roads.

A Fuel Economy Test Example

For a J1321 program with Class 8 trucks, SwRI will lease tractors and trailers unless the client furnishes the test vehicles. Leasing agencies will typically have trucks available that are powered by:

  • Cummins
  • Detroit Diesel
  • Navistar
  • Volvo
  • Mack
  • Other popular engines

Fuel consumption is measured by simulating a long-haul route (or other appropriate driving cycle), utilizing weigh tanks for fuel consumption measurement.

EPA SmartWay Experience

SwRI successfully conducted the U.S. Environmental Protection Agency (EPA) SmartWay program in support of the SmartWay Transport Partnership with the goal of reducing emissions and improving fuel economy in the transportation sector. SwRI measured fuel economy and NOx emissions on two different class 8 truck and engine configurations using the SAE J1321 protocol. A total of 38 J1321 test segments were conducted. The tests were conducted with four drive cycles, which were defined by the EPA and simulated on an oval test tracks. This program established the basis for development of the Interim test method for verifying fuel-saving components for SmartWay. The SmartWay program evaluated fuel economy benefits of single wide and low rolling resistance tires, trailer aerodynamic components including gap reduction fairings, skirts and boattail features on two types of heavy-duty diesel engines in two different class 8 line-haul trucks.

Vehicle Coastdown Evaluations

SwRI has conducted coastdown testing for the EPA and commercial clients using the method defined in the US Code of Federal Regulations (CFR) §1066.310, entitled “Coastdown procedures for vehicles above 14,000 pounds GVWR.” This test protocol is valid for calculating road-load coefficients for chassis dynamometer testing and aerodynamic input (coefficient of drag) for the greenhouse gas emissions model (GEM). Working with the EPA, SwRI engineers have enhanced this procedure and also developed a constant speed technique, measuring driveshaft torque and/or drive wheel torque for determining road load coefficients.

Related Terminology

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Benefiting government, industry and the public through innovative science and technology
Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.