The higher the compression, the more efficient the energy transfer into work, so the lower the exhaust temp for a give load.

Essentially, you are right -- the fuel is burning slower, and it's being expanded less, so it's hotter coming out.

Note that the opposite is true in turbines -- the more energy you extract (and the higher the compression ratio), the slower the gas stream moves and the higher the heat transfer to the turbine blades.

Fan jet engine turbines run incredibly hot.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!