Optimization of Automotive Exhaust Sampling Parameters for Evaluation of After-Treatment Systems Using FTIR Exhaust Gas Analyzers 2019-01-0746

Understanding the chemical reactions taking place in the engine and after-treatment systems is indispensable for minimizing harmful emissions in automotive exhaust gas. Real time gas analyzers for engine exhaust play a vital role for developing mathematical models and evaluating new after-treatment technologies. Gas analyzers using Fourier Transform Infrared Spectroscopy (FTIR) offer the advantage of continuous non-destructive simultaneous multicomponent analysis of a single gas stream. The ability of such analyzers to detect concentration fluctuations in the sample gas depends on a balance between its sample gas replacement rate and data sampling frequency. Increasing the sampling frequency is useful for detecting rapid concentration fluctuations, provided that the sample gas replacement rate is fast enough. This is commonly achieved by increasing the sample flow rate. However, such approach could be difficult during catalyst evaluation where the sample flow rate that may be extracted is limited. Recent developments in sample cell geometry and gas sampling method have improved gas replacement rate in HORIBA’s FTIR exhaust gas analyzers, without the need to increase sample flow rate. The response time and gas replacement rate of different sample cells are evaluated in this paper. Cell geometry was observed to affect the analyzer’s response time and its ability to detect rapid fluctuations of low gas concentrations. Engine exhaust emissions are analyzed on a gasoline engine test bench using two FTIR gas analyzers with different sample cell volume, gas replacement rate and sampling frequency. Data is acquired from sample points before and after the catalyst on a regulatory driving cycle (New European Driving Cycle). Concentration readings were in good correlation for both FTIR systems when the total average is calculated, but the system with the newly developed sample cell responds better during dynamic phases in the emission levels.