Questions
(6.1)
A diesel engine is fitted with mechanical injection pump with 60MPa peak injection
pressure. Another engine of the same size developing the same power is employing
common rail injection system with 160 MPa
injection pressure. Both the engines
operate at the same rated speed. Discus the likely differences
between the two engines
with respect to (i) injection duration (ii) nozzle hole size (iii) atomization and droplet
size (iv) injection timing (v) fuel eva
poration , mixing (vi) ignition delay and premixed
combustion (vii) over all combustion rates (vi) PM and NOx emissions.
(6.2)
Calculate stoichiometric NH
3
/ NO
x
ratio for reduction of NO
x
in SCR catalysts if the
entire NOx is only NO, and consists of 5 and 10% NO2 by volume. If 20 % more NH3
than stoichiometric requirements is supplied calculate ammonia slip in ppm if the NOx
concentration in the exhaust gas before conversion was 2000 ppm.
(6.3)
A diesel particulate filter (DPF) fitted to a 12 litre DI diesel engine is to be
regenerated. The engine has volumetric efficiency of 88%, is operating at 67 % excess
air and 2000 rpm. The ambient air conditions are 101 kPa and 300 K. For burning the
soot collected on the DPF, the exhaust gas temperature is t
o be raised to 540º C. The
exhaust gas temperature entering the DPF is 350º C. Determine the power of an
electric heater to raise the exhaust gas temperature to the required level if the entire
exhaust gas is to be heated. The specific heat of the gases in
the relevant temperature
range is N
2
= 30.27, CO
2
= 46.56, O
2
= 31.96, 36.44 kJ/kmol. K.
(6.4)
Given the LHV of soot = 33.8 MJ/kg , if in a DPF of 1 litre volume 10 g of soot is
burned estimate the temperature reached in the DPF. The combustion of
soot begins
at 540º C. The mass of the DPF is 400 g and its specific heat is 0.9 kJ/kg.K.
(6.5)
Refer Fig 6.20. Discuss how various technologies have helped in reduction of engine
out emissions from the diesel engines.
(6.6)
A diesel engine has BSFC = 240 g/kWh. In the engine cylinder, lubricating oil enters
through piston rings and valve guides which amounts to 0.2 % by mass of the fuel
consumption. Of the engine oil in the cylinder, 80% is burned and rest is exhausted as
SOF of particulate emissions. Es
timate the specific PM emissions solely contributed
by the engine oil. How do these compare with the Euro IV PM emission limits for
heavy duty engines?
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