Without having any engine specifics or your heat exchanger
efficiency (you didn't provide them) you could calculate
the heat available at any given time by realizing that a
diesel engine normally dumps between about 20% to 50% of
its energy out the exhaust.  Then consider the fuel burn
and air consumption rates.  That will give you an idea of
the available heat content in the exhaust.

The fuel mixture (exhaust gas composition) of a diesel
engine varies widely depending on its application,
current efficiency, fuel, RPM, boost (if turbocharged),
and power output.

That should put you in the ballpark!

Hope this helps!

Chumley

Well since it is mostly N2 O2 and CO2 we can lump them all together and say h is around 27 MJ/kmol at 600 degrees C. One kmol will be about 30 kg.


Here's the exact values for N2

T in K   h MJ/kmol

400 11.62
500 14.57
600 17.59
700 20.66
800 23.81
900 27.03
1000 30.3
1500 47.39
2000 65.24

Cheers

Greg Locock