Predicting Exhaust Gas Temperatures for Lean Burn Two-Stroke Engines
This paper focuses on the techniques used for predicting exhaust gas temperatures for lean burn two stroke engines. When planning for emissions retrofits, it is often necessary to upgrade the turbocharger system, dramatically changing the air manifold pressure and scavenging flow of the two-stroke engine. Proper matching of the turbocharger requires accurate prediction of the post retrofit exhaust gas temperatures. Predicting exhaust gas temperatures for a lean burn two stroke is difficult. Modeling the combustion and blow down process is complex and varies among unit types. Further complicating modeling is that the only reference data is typically exhaust elbow temperatures. These temperatures represent some average of blow down temperature and scavenging temperature for the unit. Hoerbigers Gas Engine Systems has developed a simplified model that combines theoretical expectations and empirical data to accurately predict post retrofit exhaust gas temperatures. The model focuses on gross combustion process analysis and then uses correction factors to tailor the results for each unit type. The model equations and matching techniques are presented in their entirety. Several case studies are presented, including the use of non-turbocharged data to predict turbocharged results.