Chassis Dynamometer Evaluation of On-board Exhaust Emission Measurement System Performance in SI Car under Transient Operating Conditions 2008-01-1826

A commercial on-board exhaust emissions measurement system, the Horiba OBS-1300, was evaluated in a series of chassis dynamometer test trails. A EURO 1 (petrol) SI passenger car, operated under normal and rich combustion conditions, and a combination of static and transient sampling provided a wide range of measurement conditions for the evaluation exercise. The chassis dynamometer facility incorporated an ‘industry standard’ measurement system comprising MEXA-7400 gas analyzer and CVS bag sampling system which were used as ‘benchmarks’ for the evaluation of both OBS-1300 component (exhaust flow meter and species analyzer) measurements and ‘daughter’ emission measurements for regulated gas-phase species (CO, CO₂, HC and NO_x).

Trials demonstrated very good to reasonable agreement for exhaust flow and CO, CO₂ and HC concentration measurements during static (R² ≈ 0.97, 0.99, 0.99 and 0.97, respectively) and transient (R² ≈ 0.88, 0.96, 0.95 and 0.86, respectively) testing. Transient emission measurements of CO, CO₂ and HC were generally consistent with ‘parent’ exhaust and species analyzer measurements (R² ≈ 0.89, 0.89 and 0.81, respectively). Minor issues associated with exhaust flow measurement error at engine ‘tick-over’/idle and HC measurement agreement under different engine operating conditions are discussed. However, in general, the OBS-1300 provided a reliable measure of CO, CO₂ and HC exhaust emissions under all conditions investigated.

By contrast, the OBS NO_x sensor cross-sensitivity to NH₃ hindered the reliability of NO_x data, especially under rich engine operation conditions.