Measurement of the effects of the exhaust gas recirculation delay on the nitrogen oxide emissions within a turbocharged passenger car diesel engine

Abstract

Fast-response nitrogen oxide (NO _x ) and carbon dioxide (CO₂) analysers have been used to study the effects of exhaust gas recirculation (EGR) delay within a modern diesel passenger car. These analysers have response times of the order of a few milliseconds, allowing the CO₂ analyser to be used to study the effects of the EGR transit delay during engine transients and the effect of sudden EGR valve actuation during a drive cycle. The effect of the EGR system delays on the NO _x emissions was measured with the fast-response NO _x analyser. The results indicate that the EGR delay contributes to the sharp short-duration spikes of NO _x .

Tests have also been carried out to identify the transient cylinder-to-cylinder EGR distribution by comparing the CO₂ concentrations in the inlet ports, again using the fast-response CO₂ analyser. The results of these tests show a variation between the CO₂ concentrations in the intake ports, suggesting a poor EGR distribution under certain conditions.

Measurements have been recorded of the EGR in the intake port runner of just one of the engine’s cylinders and have been compared with the exhaust port NO _x emissions. This provided some data on a cycle-by-cycle basis including the number of engine cycles required for the burned gas to complete the EGR circuit.