EME4096 Assignment 2 (Final Answer)

7/21/2019 EME4096 Assignment 2 (Final Answer)

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EME4096 Internal Combustion Engines ASSIGNMENT 2

Trimester 3, 2013/2014 EPP2

EME4096 Assignment 2

Question 1

a) A six-liter, eight-cylinder, four-stroke cycle SI race car engine operates at 6000RPM using stoichiometric nitromethane as fuel (A/F = 1.7). Combustion

efficiency is 99%, and the fuel input rate is 0.198 kg/sec. Assume the density ofair is 1.181 kg/m3. Calculate:

i. volumetric efficiency of the engine, (%),[95 %] [0.15 marks]

ii. flow rate of air into the engine, [kg/sec],[0.3366 kg/sec] [0.05 marks]

iii. heat generated in each cylinder per cycle, [kJ],[5.35 kJ] [0.2 marks]

iv. how much chemical energy there is in unburned fuel in the exhaust,[kW].

[21.6 kW] [0.2 marks]

b) A 6.2-liter, V8, four-stroke cycle SI engine is designed to have a maximumspeed of 6500 RPM. At this speed, volumetric efficiency is 88%. The engine is

equipped with a four-barrel carburetor, each barrel having a discharge

coefficient of CDt = 0.95. The fuel used is gasoline at AF = 15.1 (density of

gasolineg= 750 kg/m3and density of air a= 1.181 kg/m

3). Calculate:

i. Minimum throat diameter needed in each carburetor venturi, [cm].[2.224 cm] [0.3 marks]

ii.

Fuel capillary tube diameter needed for each venturi throat if tubedischarge coefficient CDt= 0.85 and the capillary tube height differential

is small, [mm].

[1.016 mm] [0.35 marks]

Question 2

The divided combustion chamber of a two-liter, four-cylinder, lean-burn, stratified

charge SI engine have 22% of clearance volume in the secondary chamber of each

cylinder. The intake system delivers an air-gasoline mixture into the secondary chamber

at an equivalence ratio of 1.2 and into the main chamber at an equivalence ratio of 0.75.The engine has a volumetric efficiency of 93%, overall combustion efficiency of 99%,

indicated thermal efficiency of 52%, and a mechanical efficiency of 86% when

operating at 3500 RPM. Assume the density of air is 1.181 kg/m3. Calculate:

a) overall air-fuel ratio,[AFoverall= 17.2] [0.4 marks]

b) overall equivalence ratio,[0.849] [0.05 marks]

c) brake power at this condition, [kW],[70.15 kW] [0.4 marks]

d) bmep, [kPa],[1203 kPa] [0.1 marks]


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e) amount of unburned fuel exhausted from the engine, [kg/hr],[0.133 kg/hr] [0.15 marks]

f) bsfc, [gm/kW-hr].[189 gm/kW-hr] [0.15 marks]

Question 3

a) A four-cylinder SI engine with a compression ratio rc= 10 operates on an air-standard Otto cycle at 3000 RPM using ethyl alcohol as fuel. Conditions in the

cylinders at the start of the compression stroke are 60 oC and 101 kPa.

Combustion efficiency %97c

. Write the balance stoichiometric chemical

equation for this fuel. Calculate:

i. the AF if the engine operates at an equivalence ratio 10.1 ,[8.18] [0.15 marks]

ii.

peak temperature in cycle of part (a), [

o

C], [3941 oC] [0.35 marks]iii. peak pressure in cycle of part (a), [kPa].

[12 789 kPa] [0.1 marks]

b) A six-cylinder, four-stroke cycle SI engine with multipoint fuel injection has adisplacement of 2.4 liters and a volumetric efficiency of 87% at 3000 RPM, and

operates on ethyl alcohol with an equivalence ratio of 1.06. Each cylinder has

one port injector which delivers fuel at a rate of 0.02 kg/sec. The engine also has

an auxiliary injector upstream in the intake manifold which delivers fuel at a rate

of 0.003 kg/sec to change the air-fuel ratio and give a richer mixture when

needed. When in use, the auxiliary injector operates continuously and suppliesall cylinders. Assume the density of air is 1.181 kg/m3. Calculate:

i. time of one injection pulse for one cylinder for one cycle, [sec],[0.00242 sec] [0.3 marks]

ii. the AF if the auxiliary injector is not being used,[8.49] [0.05 marks]

iii. the AF is the auxiliary injector is being used.[6.01] [0.3 marks]

Question 4

a) A two-liter, four-cylinder, open-chamber SI engine operates at 3500 RPM usingstoichiometric gasoline. At this speed, volumetric efficiency is 93%, combustion

efficiency is 98%, indicated thermal efficiency is 47%, and mechanical

efficiency is 86%. Assume the density of air is 1.181 kg/m3. Calculate:

i. brake power, [kW],[74.74 kW] [0.45 marks]

ii. bmep, [kPa],[1281 kPa] [0.1 marks]

iii. amount of unburned fuel exhausted from the engine, [kg/hr],[0.316 kg/hr] [0.15 marks]

iv. bsfc, [gm/kW-hr].[211 gm/kw-hr] [0.15 marks]


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b) The spark plug in the cylinder of an SI engine is fired at 20 obTDC when theengine is running at 2400 RPM. Flame propagation mode starts at 10obTDC and

last for 0.001667 seconds. Calculate:

i. time of ignition and flame development in degrees of engine rotation,[degree],[10 degree] [0.1 marks]

ii. time of ignition and flame development in real time, [sec],[0.000694 sec] [0.1 marks]

iii. crank angle when flame propagation mode ends, [degree after top deadcenter].

[14 degree aTDC] [0.2 marks]

End of Paper

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EME4096 Assignment 2 (Final Answer)