Overview
The project aimed to define an effective procedure to determine pollutant emission from helicopter engines during different flying conditions. The basic strategy was to couple detailed kinetics, needed to determine those components which are present in a low or very low concentration, with detailed fluidynamics necessary to describe in an accurate way the thermal and fluid flow fields, which control the pollutant formation/reduction. After an accurate analysis of the state of the art, starting point of the activity was the definition of the helicopter surrogate fuel and the development, tuning and validation of their combustion kinetics. The resulting detailed mechanism was the starting point for the construction of an optimised global few step kinetic mechanism to be used in CFD computations.
The CFD simulations were based on the global mechanism, the combustor geometry and flying conditions. The temperature and flow field coming from CFD and the detailed kinetic scheme were the input for the postprocessing activity for the pollutant emission estimation. Effective and parallel numerical algorithms increase the performances of such a time-consuming activity. Several CFD and postprocessing computations in the different flying allow to compare with experimental results. In this procedure some iterations could be necessary. The fluidynamic results can show the need of detailed and/or global kinetic refinements. As a consequence, the output of CFD computations can impact on detailed kinetic scheme development and validation and/or to the global few step mechanism. Again, over or under-estimations of the emissions from postprocessor could require revising either the kinetics or the CFD.
Funding
Results
Executive Summary:
The project aimed to define an effective procedure to determine pollutant emission from helicopter engines during different flying conditions. The basic strategy is to couple detailed kinetics, needed to determine those components which are present in a low or very low concentration, with detailed fluidynamics necessary to describe in an accurate way the thermal and fluid flow fields, which control the pollutant formation/reduction.
After an accurate analysis of the state of the art, the helicopter surrogate fuel was defined and the its combustion kinetics was developed, tuned and validated. The resulting detailed mechanism was the starting point for the construction of a flame let database used in CFD computations. The CFD simulations were based on the combustor geometry of the Rolls Royce-Allison Model 250. This engine is a highly successful turbo-shaft engine family, which propels a large number of helicopters (including the Agusta A 109 and PZL SW-4). The helicopter model PZL SW-4 RR250C20R2 has been recently selected for an experimental campaign by the research team involved in the FP7 CLEAN-SKY project MAEM-RO (g.a. 267492). Therefore, this engine was studied to characterize the formation of unburned hydrocarbons (CO, PAH and soot), which reduces the combustion efficiency and consequently increase the fuel consumption and NOx. In particular, the NOx emissions from this engine are calculated for different power levels, form idle to take off conditions, and compared to available literature measurements.
The CFD results, in terms of temperature and velocity profiles, were postprocessed by a specific homemade tool (KPPSMOKE), able to account for the detailed chemistry involved in pollutant formation.
These computations require a significant amount of cpu times and thus specific numerical algorithms, and parallel approaches were developed to improve the computation performances.
The developed model, which is fully predictive and does not require tuning parameters or any adjustments, resulted a powerful tool to predict emissions, showing a satisfactory agreement with the experimental measurements in different flying conditions.