Dan
Take a look at a Masters Thesis by Y.Li on "Assessment of Vehicle Fires in NZ Parking Buildings"
see
www.civil.canterbury.ac.nz/fire/fe_resrch_reps.shtml#2004 The Literature Review in this thesis comprehensively details experimental work done on car fires worldwide, including fires in enclosed car parks (also includes pictures which you can reference).
There have been two Journal papers produced from this work which may be of interest:
Li, Y., Spearpoint, M. J., Cost-benefit analysis of sprinklers for property protection in New Zealand parking buildings, Journal of Applied Fire Science, v12no3, 2006:223-243
Li, Y., Spearpoint, M. J., Analysis of Vehicle Fire Statistics in New Zealand Parking Buildings, Fire Technology,Vol 43, No 2, 2007:93-106