Questions
(5.1)
What is the significance of space velocity of a catalytic converter? A gasoline car powered
by a 1.2 litre swept volume engine is fitted with a catalytic converter of 1.2 litre
. The
maximum speed of the engine is 5,500 rpm and when operating at maximum load it has
volumetric efficiency of 0.8. Taking inlet conditions as 100 kPa, 300K and stoichiometric
mixture, calculate the maximum space velocity encountered in the converter if
the exhaust
gas enters the catalyst at 500 K. Take gasoline as octane.
(5.2)
In the above converter, exhaust gas with 1.2% CO and 1000 ppmC1 HC enters. If
conversion efficiency of the converter is 90 % for CO and HC, estimate increase in the gas
tempera
ture under steady state operation of the engine and converter. The LHV of gasoline
is 44 MJ/kg and of CO is 10.1 MJ/kg. The specific heats of gases are: N2 = 33.75, O2
=
35.59, CO2 = 55.37, H2O = 44.94 kJ/kmol.K
(5.3)
In a gasoline car exhaust gas with 9.0, 0.8 and 0.6 g/km of CO, HC and NO
x
enters the 3-
way catalytic converter. During city trip of 15 km for the first 1.5 km the exhaust gas
temperatures being low the catalyst has overall only 20% conversion efficiency.
For the
remaining trip, efficiency of conversion is 85%. Find the average vehicle emissions for the
trip in g/km.
(5.4)
An inventor claims that he has developed a non-catalyst thermal reactor when fitted in the
exhaust muffler converts HC and CO by 50%. U
nder the full engine load peak combustion
pressure are about 40 bar and temperature is 2500 K. Under the other conditions the peak
combustion temperatures and pressures would be lower than these. The exhaust blows
down to 1.1 bar pressure. The polytropic i
ndex of expansion process is about 1.28. As the
gas flows through the exhaust pipe its temperature falls by 50% when it reaches the exhaust
muffler. The residence time for the exhaust gas in the muffler is 100 ms. In view of the
above information verify the acceptability of these claims.
(5.5)
An engine misfires and HC concentration in the exhaust gas suddenly rises to 50,000
ppmC1. Estimate the extent of sudden increase in the gas and catalyst temperatures for a
ceramic monolith converter. The converter
volume is 0.85 litre, mass 340 g, specific heat is
0.9 kJ/kg. K.
(5.6)
If the engine in Problem 5.5 is fitted with metal monolith converter of the same size having
mass of 680 g and specific heat of 0.5 kJ/kg.K what would be the maximum temperatures
reac
hed. Assume the unburned HC are like gasoline in composition and have the same
LHV as given in Problem 5.2.
(5.7)
For cold start emission control discuss the advantages and disadvantages of the closed
coupled catalysts, electric heated catalysts and HC traps.
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