Combustion Modeling

During my career I have never been an “active” combustion modeler, but combustion modeling has always been a part of the engineering discipline in organizations I have worked in or with throughout my career.  I have always been more of an experimentalist than a modeling type but appreciate the continued improvements and possible insights the more recent models are bringing to understanding combustion.  I’m optimistic of it’s value for the future.

This combustion  modeling discussion is in reference to the actual combustion process in the combustion chamber and not the modeling of the boosting and intercooling  models that predict the trapped charge.  On the later,  the fidelity of the fluid dynamics and flow process modeling has historically had a much higher fidelity and value!

My historic skepticism of combustion models relates to the complexity of the process and what is often the over valuing the results and or the reliance of the model to predict things the models  are not capable of discerning.  There has been a tendency to credit the fidelity of past models to the confirmed results being within a few percent of the experimental results.  However the reality of the situation is if the air fuel ratio is known and the combustion bowl, air motion and injector configuration are of a know “viable configuration”  a simple heuristic can often predict the performance to a similar accuracy.  Historically the early models of diesel combustion with their concentric layers of stoichiometry were to used almost religiously in constructing models believed to be accurately predicting “what’s going on in there”, however the more recent models, more reflective of  what I refer to as the Sandia Lab/JohnDec model, look quite different and come much closer to representing what might be deduced from experimental observation.

A most recent advancement, that I have observed, that can play an important role in  understanding the nuances within the diesel combustion process, is the use of virtual reality observation of the process.   I have often found the 2 dimensional cross sectional views of modeled results of limited value in bringing engineers together to agree to subtleties of the diesel combustion process.  However, viewing the process  in slow motion in 3 dimensional space is an all together different situation!

To have a group of engineers in a room in virtual reality space within a modeled combustion chamber, all being able to see the dynamic injection and combustion process from all angles and cross sections within the modeled combustion chamber, is an outstanding improvement to the usefulness of the modeling process.  Such a tool can  fuel dialogue between engineers as to what potentially is going on as they observe the process in slow and stop motion as they dissect areas of the combustion process switching between variables such as stoichiometry, temperature, and gas constituents and perhaps even toggling between incremental change of the system!

While such a modeling experience is only as precise as the model itself, with the continued improvement of models, I see the future value of such a tool to drive both incremental improvement of today’s combustion systems, and also to support investigation of creative new ideas.  Such work continues to need to be supplemented by good experimental observations withing the combustion chamber and or spray and combustion bombs and engine confirmation.