See the following paper for one possible methodology:

http://link.springer.com/article/10.1007%2Fs11081-009-9090-6#page-1

Agree with Michael - basically you create a merit function for engine optimization in terms of exhaust emissions.

What you could do is basically:

1) Measure the given exhaust emissions for different operating conditions

2) Put them inside you merit functions which allows you to compare your operating conditions

This is especially interesting if you fix your rpm and engine load, and then play with other parameters, such as injection pressure, injection timing, exhaust gas recirculation, because here you can compare the different parameter choices.

You can go even further and perform statistical methods (Design of Experiments, combined with an analysis by linear multiple regression) in order to create functions which show you the dependency of different emisisons from the parameters you have chosen. When you combine these functions with your merit function you can virtually create engine fields and optimize your engine in terms of all parameters together.

This explains also the choice of your merit function. It needs to a) take into account all the values (here: emissions) which matter to you, b) bring them to a comparable size (by normalizing) and c) be ntegrated in a function which can be easily optimized (as done in the equations you have shown).

I hope this short explanation is helpful. If you have further questions, do not hesitate!

Exponents indicate the weights that have been assigned to different non-dimensional parameters. These weights can be decided based on several conditions, for example, relative importance of each parameter on the process to be optimized, combustion properties etc.

thank you dear friends . i got the answer .

mr Rakesh Mishra has the best answer . yes it is related to weight factors of each parameter and the importance in the optimization .

thanks again .

Merit function is a fucnction of

1)Engine parameters ike injection pressure, injection timing, compression ratio, engine speed, engine load ,

2)fuel paramters like type of fuel, calorific value, specific gravity, cetane number, viscosity, type of induction of fuel, fuel operating condtion 

3) Congiguration of the enginelike stratified engines, supercharged engines,etc 

4) Method of cooling, method of lubrication  

I agee with Prof.Marek Mazur, regarding adopttability of merit function of IC engine