In-Cylinder Equivalence Ratio & Temperature Evolution
The engine in-cylinder mixture is represented by using a Probability Density Function (PDF) method – this function is made up of representative multiple air-fuel parcels or more precisely if using the mathematical definition – stochastic particles. One extreme is to use a single particle – which is analogous to a single zone model. However modern IC engines are highly stratified (in terms of temperature and fuel stratification) thus in order to simulate combustion and emissions more robustly we must apply a carry out a more detailed analysis.
In the same way as with 3D CFD, as you increase the amount of refinement used to represent the in-cylinder mixture, you reach a convergence in your solution. Using 100 particles has proven sufficient for almost all of the hundreds of IC engine applications simulated using the tool, if you compare this with the number of cells required to reach convergence in 3D CFD (10,000s) and you gain some insight as to how we can achieve such large orders of magnitude in CPU time speed-up for equivalent performance and emissions.
To demonstrate the application of the srm engine suite for different IC engine applications we present an animation of each operating mode below. Each animation presents the evolution of the PDF as a function of time over local in-cylinder temperature and equivalence ratio. Each simulation was carried out at the same speed-load point with a summary of the operating condition presented in the table below.
In each case a compression, heat transfer, turbulent mixing and injection event is simulated followed by fuel oxidation and emissions formation via the solution of a user defined chemical kinetic sub-model. Each mark represents the local composition for each stochastic particle. As might be expected, the PDF for each operating mode has evolves differently – for example the CIDI operating mode has regions of the mixture which are ultra rich (φ>3.0) ultimately leading to higher PM formation rates.
The following particle animations were generated using the srm engine suite for a variety of fuels and engine operating conditions (all operating at 1500 RPM, 2.6 BMEP, 30% EGR). These visualisations are a unique feature of the srm engine suite, which offers the user a measure of the inhomogenity (temperature and composition) in the cylinder and helps identify sources of soot, NOx, etc. in the engine.