Search Results

The measurement of vehicle modal emissions is technically challenging due to the major issue of determining exhaust gas mass flow rate and ensuring that it is synchronous with the emission measurement of that corresponding ‘slug’ of exhaust gas. This is very evident when attempting to measure small passive NOx catalyst conversion efficiencies. This paper highlights alignment issues with regard to the variation of time delays associated with engine and vehicle events and the CO2 tracer method for determining exhaust gas flows.

Time-alignment sensitivity studies have been carried out to assess the accuracy of instantaneous mass NOx emissions on a chassis rolls dynamometer. The work is part of a larger project aimed at measuring passive NOx catalyst conversion efficiencies. Instantaneous NOx emissions are examined in relation to the NEDC vehicle speed trace at multi sampling points, and phase and time alignment issues are highlighted and discussed. It has been found that a small mismatch of the vehicle speed trace to the instantaneous mass of emissions of ± 2 seconds can lead to results indicating that the conversion efficiency is anywhere between 0-20%. Finally, examples are presented showing the difficulties of attempting to adjust the time alignment of raw emissions data.

The regulated and non-regulated emissions of a current diesel passenger car and two light-duty diesel trucks with catalysts and particulate traps were measured to better understand the effects of aftertreatment devises on the environment. The passenger car, a 1.8 L IDI TC Sierra, was tested both with and without three different diesel oxidation catalysts (DOC) and with two fuel sulfur levels, 0 and 0.05 wt%. One light-duty truck, a 2.5 L DI NA Transit, was tested on one fuel, 0.05 wt% sulfur, with and without three different particulate trap/regeneration systems and with and without a urea lean NOx catalyst (LNC) system. A second similar Transit was tested on the 0.05 wt% sulfur fuel with an electrically regenerated trap system. The results are compared to each other, regulated emission standards, and to emissions from gasoline vehicles.