CFD analysis of novel variable compression ratio rotary engine

摘要

In compression ignition engines, the soot-NOx paradox is an extremely challenging unresolved issue. Homogeneous Charge Compression Ignition (HCCI) is one of the most promising solutions that combine the benefits of both Spark ignition and Compression ignition combustion modes. Fuel-lean premixed combustion helps to reduce or eliminate the formation of NOx and soot. HCCI engines have a high heat release rate at high load that results in knock. A unique variable compression ratio rotary engine based on the HCCI combustion mode (patented by Customachinery Inc) is under development at Queen's University. The present study includes a computational fluid dynamics analysis of the air induction and compression, fuel injection, fuel and air mixing, and ignition process using Ansys Fluent. A unique dynamic mesh was adopted that allowed for the modeling of a fixed stator and rotating lobed rotor, as well as novel gates that extend and retract. A default Fluent fuel spray model was used and the optimum fuel injector location and orientation were determined. Two different combustion models (single-step and detailed chemistry) were investigated, and it was found that the results have significant differences. The detailed chemistry predicted a two-stage ignition process typical for heptane fuel that a single-step model cannot predict. The effect of other parameters such as compression ratio, fuel load, and fuel injection time on the ignition and combustion process were also studied.