A chassis test procedure to mimic the heavy-duty engine transient emissions certification test

Area of Science:

• Environmental Science
• Mechanical Engineering
• Automotive Engineering

Background:

• In-use emissions from heavy-duty diesel engines often exceed certification levels due to component degradation, poor maintenance, after-treatment system failures, or tampering.
• Direct comparison of in-use emissions with certification levels requires engine removal and dynamometer testing, which is impractical for in-use vehicles.

Purpose of the Study:

• To develop a chassis dynamometer test procedure that accurately simulates engine performance and emissions levels from the official engine certification test.
• To evaluate the effectiveness of this chassis test in identifying engines with elevated emissions, particularly those affected by tampering or poor maintenance.

Main Methods:

• Emissions data were collected from two heavy-duty diesel engines using the transient Federal Test Procedure (FTP) on an engine dynamometer.
• The same engines were tested in-vehicle on a chassis dynamometer using a driving schedule designed to replicate the engine FTP's torque and speed.
• Testing included stock (unmodified) engines and configurations simulating tampered or poorly maintained conditions.

Main Results:

• The chassis test effectively predicted nitrogen oxide (NOx) emissions above certification levels using engine-specific correction factors.
• Identification of gross particulate matter (PM) emitters was possible, though data scatter limited precision.
• The chassis test successfully identified increased NOx and PM emissions resulting from engine tampering and poor maintenance.

Conclusions:

• A chassis test procedure is a valuable tool for predicting whether an engine in a vehicle would pass certification emissions tests.
• The chassis test can identify engines with elevated NOx emissions and gross PM emitters, especially when affected by tampering or poor maintenance.
• The correlation for carbon monoxide (CO) and hydrocarbon (HC) emissions was insufficient to support the chassis test for screening these pollutants.