146336_EME4096 MidTerm Test 2

Question 1

a) A race car burns nitromethane with air at an equivalence ratio of 1.25. Except for unburned fuel, all nitrogen ends up as N 2  and all carbon ends up CO 2  (no CO). Calculate: i.

ii. iii.

Write the balanced chemical reaction equation, [Answer: CH3 NO2+0.6O2+(0.6)(3.76)N2>0.8CO2+1.2H2O+2.656N2+0.2CH3 NO2, 7 marks] Percent stoichiometric air [%], and [Answer: 80% stoichiometric stoichiometric air, 3 marks] Air-fuel ratio. [Answer: 1.36, 3 marks]

 b) Methanol is burned in an engine with air at an equivalence ratio of   =   = 0.75. Exhaust  pressure and inlet pressure are 101 kPa. Calculate: i.

ii. iii.

Write the balance chemical equation for this reaction, [Answer: CH3OH+2O2+(2)(3.76)N2>CO2+2H2O+(2)(3.76)N2+0.5O2, 6 marks] Air-fuel ratio, and [Answer: 8.63, 3 marks] Anti-knock index of methanol. [Answer: 99, 3 marks]

Question 2

A small in-line, four-cylinder, 2.2 L, CI automobile engine equipped with cylinder cutout, operates on a four-stroke Dual cycle using light diesel fuel with AF = 21. When very little  power is required re quired the engine converts to a two-cylinder 1.1 L engine and operates at a higher speed. As a four-cylinder, the engine runs at 2100 RPM, with a volumetric efficiency of 61%, and a brake thermal efficiency of 45%. As a two-cylinder, the engine has a volumetric efficiency of 82%, and a brake thermal efficiency of 42%. Combustion efficiency is 98% at all times. Density of air is 1.181 kg/m 3. Calculate: i. ii. iii.

Flow rate of air into four-cylinder engine at 2100 RPM [kg/sec], [Answer: 0.0277 kg/s, 6 marks] Flow rate of air into two-cylinder engine to produce same brake power output [kg/sec], and [Answer: 0.0297 kg/s, 13 marks] Speed needed as two-cylinder engine to produce same brake power [RPM]. [Answer: 3348 RPM, 6 marks]

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