Post-oxidation model validation with utilization of estimated hydrogen by easily measurable gas species and chemical equilibrium

Abstract

Post-oxidation phenomena have become an alternative potential solution to reduce engine-out emissions while improving turbocharger performance, especially in cold-state operation. Hence, it is essential to investigate each parameter in detail that significantly influences the post-oxidation phenomena. In-cylinder hydrogen (H₂) formation and its reaction in the exhaust manifold are the key parameters that significantly influence the post-oxidation phenomena in the exhaust manifold, as exhaust enthalpy increases due to H₂ consumption. However, it is still difficult to measure the accurate H₂ concentration in the cylinder and exhaust manifold due to the few commercially developed sensors available, which also poses uncertainty and a complex measurement methodology. Hence, in this research, an H₂ estimation methodology was adopted and discussed, which can be utilized for the easily measurable emissions (i.e. measured from an exhaust gas analyzer (HORIBA MEXA1600) and chemical equilibrium constant relation for H₂ estimation by the iteration method. The estimated H₂ was validated with a mass-spectrometry-type hydrogen sensor. Then, this estimated H₂ can be used as an input parameter in the post-oxidation model validation in a wider range of operating conditions, which can be convenient and cost-effective to understand the post-oxidation phenomena in a full engine mapping without involving complex and expensive experiments. The post-oxidation model and estimated H₂ were compared with the experimental data of a 4-cylinder turbocharged GDI engine, and it seems to be in a reasonable range except for some typical operating conditions. Also, it can be stated that the estimated H₂ is more authentic than the measured H₂, as the commercial H₂ sensor is in the early stage of development and highly sensitive to environmental pressure, temperature, and tedious to use, which can cause several errors in the data. However, on the other side, the emissions measured with the exhaust gas analyzer, which is being used for the H₂ estimation, are consistent and do not significantly depend on the environment.