Most of the recent clean diesel engines are equipped with an
exhaust gas recirculation (EGR) technology in order to meet the
strict criteria of NOx and particulate matter (PM) as required in
the current emission regulations. More attention to strict EGR
control is becoming required. Accurate and fast transient EGR ratio
operation is becoming very critical in the field of the emission
control.
The EGR ratio is typically monitored by CO₂ trace method, in
which CO₂ emitted from engine, is utilized as a tracer gas. The EGR
ratio can be obtained from CO₂ concentration measured at engine
intake and engine out at the same time. In this study, authors have
developed a new EGR analyzer consisting of two CO₂ detectors, to
achieve required performance for transient measurement, i.e., short
delay time and quick response, negligible difference between two
CO₂ detectors, and capability of wet measurement. For this new
analyzer, heated NDIR detectors which can measure CO₂ in engine
emission under wet condition were adopted. The sample lines for
each CO₂ detector were configured to have small volume and also
almost same design as each other, to avoid transient errors caused
by the difference in response time.
We have evaluated the performance of the transient EGR analyzer
through some comparison tests with a conventional exhaust gas
analyzers system. In consequence, the faster response has been
observed from the transient EGR analyzer without significant
transient error under several test cycles. Furthermore it has
proved that effects on response time from the sample inlet pressure
change are significantly small. Finally the EGR ratio measured by
the transient EGR analyzer followed up the EGR valve operation
well. These results show the advantages of the transient EGR
analyzer for measuring EGR ratio under transient state.