“Fuel consumption is a very complicated element to measure, especially when it comes to diesel engines,” says Yves Provencher, director of the FPInnovations’ Performance Innovation Transport (PIT) Group, a not-for-profit engineering and research group that serves fleets and suppliers in the North America trucking industry. “With the advent of electronically controlled engines, many truck fleets have used data on fuel consumption from engine Electronic Control Modules (ECM), but it should be used with caution for evaluating the impact of a fuel saving technology.”
Original equipment manufacturers provide fuel consumption data via the ECM using comprehensive algorithms, Provencher relates. Those calculations take into consideration parameters such as engine speed, road speed, distance, and fuel volume used, among other factors. However, he cautions, no technical information has been found containing engine manufacturers’ statements regarding the accuracy or the precision of ECM fuel consumption data.
“Fuel consumption data in an ECM derived from an algorithm and not from actual fuel flow does not account for fuel energy content, density or temperature,” Provencher continues, “so there is an inherent error with those calculations. In verbal communication, domestic engine manufacturers seem to concur on a +/-4% error factor, although no scientific evidence was ever provided confirming those statements.”
ECM data can be useful for creating driver profiles and monitoring their activity relative to idle time, shifting, harsh and acceleration, speeding, etc., Provencher notes. The ability to measure fuel consumption accurately and precisely and defend the results, though, is critical for writing vehicle specifications, for establishing effective maintenance practices, and for training drivers to operate vehicles as fuel efficiently as possible.
In the fall of 2014, to compare engine ECM data with actual fuel consumption, the PIT Group conducted test track fuel consumption evaluations involving 14 different vehicles with engines from Cummins, Detroit, Mercedes and Volvo. The tests followed the Joint TMC/SAE Fuel Consumption Test Procedure Type II described in SAE J1321 , a fuel measurement method that allows for test accuracy within 1%.
The results of the gravimetric measurement, converted to fuel volume, were compared with the fuel consumption data provided by the engine ECMs, which was retrieved using onboard computers or engine scan tools. Fuel specific gravity was measured with a hydrometer.
“These tests showed that ECM data precision and accuracy varies between engine manufacturers and among engine models from a single manufacturer,” Provencher reports. “For a given vehicle, ECM data precision and accuracy will even vary from test to test.
“ECM accuracy and precision measurements under controlled test track conditions are more reliable when averaging data over a larger number of test runs,” Provencher adds. “In real world operations, however, other factors such as traffic, road condition, weather and payload will impact fuel consumption.”
Fleets interested in the full report on the PIT Group’s study comparing engine ECM data with actual fuel consumption can visit www.thepitgroup.com. Also available is information on fleet membership in the testing organization, which includes engineering services and access to test results from Energotest, the PIT Group’s certification process for fuel saving technologies.