Figure 12.

Engine brake thermal efficiency maps for a c. 2007 PFI engine (top) and an advanced boosted downsized engine with cooled EGR (bottom). An energy-weighted heat map of the engine operation during the combined FTP and HW cycles is shown superimposed on each BTE map. The heat map represents a histogram of fuel energy expended in small polygonal areas of the map, with dark red being the highest energy expenditure and dark blue the least. For reference, lines of constant power are indicated in gray, and the line of maximum efficiency at each power is indicated in magenta. These maps are for a relatively small engine (i.e. low P/W ratio or low power/tractive load ratio) – compare to Figure 11.