Assignment 2

1.Running the case at 1800 rpm and following parameters are noted down :

A. First running the tutorial SI engine calibration at given 1800 rpm and following parameters are noted down :

• Air flow rate : The amount of air (in kg) flow flowing in the cylinder per hour is 24.6(kg/h)
• BMEP : The brake mean effective pressure (BMEP) is what we have at the crankshaft. BMEP is the difference between indicated mean effective pressure (IMEP) and “friction” mean effective pressure (FMEP). Hence, BMEP = IMEP-FMEP=10.61-1.13=9.48 bar
• BSFC : Measure of fuel efficiency within a shaft reciprocating engine. It is the rate of fuel consumption divided by the power produced. It is 239.2g/KW-h
• In-cylinder pressure : The maximum pressure that cylinder reaches during combustion process is 48.86 bar

Pressure vs Crank diragram (P vs θ graph for incylinder pressure )

2. Increase the power output at 3600 rpm by 10%

The power at 3600 rpm for given tutorial is noted down as 22.4 HP. Hence an aim of acheiving an increase of 10% would be close to 24.6 HP

i. Changing the air-fuel ratio :

As we make a rich mixture of A/F ratio it's power o/p is increased but at cost of emission increase of CO

Hence, on further making a rich mixture we can raise the power o/p to 24.6 but there will be a drastic increase in CO as emission

ii. Changing the compression ratio :

By increasing the C/R from 9.5 to 15.5 we can raise the power output to 24.6. But this will lead to increase in knocking in SI engines hence not feasible.

iii. Changing the geometric conditions i.e. bore diameter and stroke length :

a. By changing the bore dia: By raising the bore dia from 86 to 90 mm we obtain an increase of power O/P to 24.6 HP

b. By changing the stroke length: By raising the stroke length from 86 to 95 mm we obtain an increase of power O/P to 24.6 HP

By Far, the most feasible and convenient method would be to change the cylinder geometry, along with these other factors like proper lubrication, super and turbo-charging, injector size can be performed to raise the power O/P.