Certification of heavy-duty diesel requires engines to be tested on an engine dynamometer and meet certification in accordance with specific procedures and cycles. However, real-world emissions have been observed to be significantly different from in-laboratory testing. The brake-specific emissions from vehicles are influenced by various operating parameters such as engine speed, load, traffic flow and ambient conditions, hence, vary from the values obtained from the certification tests. In the future, US EPA and other state regulating bodies will require the engine manufacturers to measure in-use emissions from vehicles operating under “real-world” operating conditions.
A test vehicle instrumented with West Virginia University's (WVU) Mobile Emissions Measurement System (MEMS), a portable onboard tailpipe emissions measurement system, was used to obtain engine operating conditions, vehicle speed and in-use emission rates of CO2 and NOx. The vehicle was driven on a specific route, which included a mix of highway and city driving patterns.
Analysis was performed to determine the amount of time the engine spent in the NTE (Not-to-Exceed) zone of operation, and also over continuous 30s windows of NTE zone operation for the different driving routes. An attempt was made to establish a relationship between the time spent in the NTE region, and excursions in brake-specific emissions.
Modal analysis was performed to determine the episodic nature of events and emissions during engine operation within the Not-to-Exceed (NTE) zone of operation, for each of the selected routes. The contribution of each mode of operation to variations in emissions rates has been documented.
Analysis was performed to determine the effect of employing 30s, and the continuous windows on work done, and the consequent effect on brake-specific emissions in the NTE zone of operation. Results indicate a difference in the number of NTE windows of operation, and also in values of brake-specific emissions calculated by the two methods.