As for cleaning grime or film (i.e eyebrow) from a vehicle with an inverted-L, I don't believe this is possible due to the inherent design flaw of the L; a portion of the spray from the top and side nozzles crashes into each other and wrecks the pattern.
As for chemistry, I learned a long time ago to leave the chemistry to the chemists. However, I am providing some quotes from John Lenhart. Lenhart is a chemical consultant and has develop products for Dow, P&G, Dial and others. I have followed his guidance for years and it has worked well for me and the clients that I advise.
In general, the ultimate reactive combination is acid and alkaline.
"The most reactive configuration would consist of one step of an organic acid at high temperature, high concentration and long dwell time. The other step would consist of an inorganic alkaline at high temperature, high concentration and long dwell time."
"The order of the two steps is dependent on the objective of the operator. If the objective is cleaning with the least amount of damage to the vehicle's surface, then the acid will be first. If the objective is to produce a dry vehicle, then the acid will be last."
There are four possible chemical configurations.
High alkaline/low acid - the cleaning is done with alkaline and the only effect the acid has is to neutralize potential damage from the alkaline. Since the acid concentration is low, it will not aid in drying.
Low alkaline/high acid - this is probably what you are using to wash with friction if your focus is on drying. The alkaline attracts the acid into the soil and creates heat of neutralization.
High acid/low alkaline - acid does the cleaning and alkaline minimizes potential damage to vehicles.
Low acid/high alkaline - The acid thins the soil and prevents the alkaline from setting the soil. Cleaning is the focus with this approach.
Water temperature, dilution ratios and dwell time requirements vary considerably by machine, technology and geography and will need to be dialed in by trial and error (fine tuning).
Hope this helps.
Bob Roman
www.carwashplan.com