IC Engine Analysis: BSFC, BMEP, Power, Torque, and Efficiency

This assignment provides a detailed analysis of internal combustion (IC) engines. It begins by defining and explaining Brake Specific Fuel Consumption (BSFC), including its units, significance in evaluating engine efficiency, and comparison of BSFC values across different engine types and applications. The assignment then delves into Brake Mean Effective Pressure (BMEP), clarifying its definition, its theoretical nature, and its relationship to engine power output. It also presents typical BMEP values for various engine types. The core of the assignment involves solving numerical problems related to a four-stroke engine, calculating Indicated Mean Effective Pressure (IMEP), BMEP, Friction Mean Effective Pressure (FMEP), brake power, and torque. Finally, it addresses the power output and engine torque for a given engine, incorporating generator efficiency and calculating BMEP. The assignment utilizes formulas and data to illustrate key concepts in engine performance analysis.

Running head: IC ENGINE 1
IC ENGINE
Name of Student
Institution Affiliation

IC ENGINE 2
Question 1.
Brake specific fuel consumption is the ratio of the amount of fuel consumed to break power
developed in a unit time.
In other words, it is a measure of the fuel efficiency or how efficiency a given amount of fuel
is being converted into a specific amount of horsepower (Taylor, 2016).
Units of BSFC in SI units are,
BSCF = ¿ f
inf ( Kg
hour )
B . P ( KW )
= ¿ f
B . P { Kg
KW . hr }
Units of BSFC in English units are,
BSCF = inf ( 1b
hour )
B . P (hp)
= inf
B . P { 1 b
hp . hr }
Break power is the power available at the crank to supply to the gearbox. The magnitude of
the brake power depends on how efficient the engine cylinder converts fuel in the indicated
power and how efficient the engine parts in transferring that indicated power to the shaft
power. The lesser the frictional losses, the greater is the brake power (Taylor, 2016).
In the automotive applications, the Break specific fuel consumption is applied in the
evaluation of the efficiency of the internal combustion engines (ICE).
Let’s say we have two engines of approximately equal power. That is their respective torque
and horsepower curves are quite similar. One exhibits a BSFC curve lower than the other
engine. It means that the one with the lower BSFC curve will accelerate more quickly than
the other. It will also be more responsive to the changes affecting combustion efficiency and
require less total spark timing to perform at its best (Lumley, 2015).

IC ENGINE 3
The best and worst BSFC values an engine is likely to operate are as shown in the table
below:
Power
(KW)
Year Engine type application BSFC(1b/hp.h) BSFC(kW.h) Energy
efficiency
57 2003 Toyota 1nz.FXE
gasoline
Toyota
Prius car
0.370 225(5) 36.4%
63 1991 GM Saturn 14
engine. Gasoline
Saturn S-
Series cars
0.411 250(1) 32.5%
88 1990 Audi 2.5 L TDI Audi 100
car
0.326 198(13) 42.6%
95 1970 Lycoming O-320
piston gasoline
General
aviation
0.460 280(1) 29.3%
130 2007 BMW N47 2L
turbodiesel
BMW cars 0.326 198(12) 42.6%
Question 2.
Brake mean effective pressure refers to the average pressure which, when imposed uniformly
on the piston from top to bottom of each of the power stroke, would yield the brake
(measured) power output. The brake mean effective pressure is theoretical and has no
relationship with the actual cylinder pressures (Lumley, 2015).
The term brake mean effective pressure Even if it contains the word “pressure” is not a
pressure term but a work term.

IC ENGINE 4
Brake Mean Effective Pressure = (n × t × 2 × 3.14) / d
Where By:
n =No of Revolutions per Power Stroke
t = Torque
d = Displacement
Note:
For Two Stroke Engine n = 1
For Four Stroke Engine n = 2
Table of typical maximum values (range of values) of bmep for various engines.
Engine type BMEP at peak power( mPa)
Naturally aspirated spark ignition engines 0.85-1.05
Boosted spark ignition engines 1.25-1.7
Boosted automotive four-stroke diesel engine. 1.4-1.8
Naturally aspirated four-stroke diesel engine. 0.7-0.9
Huge low-speed diesel engines 1.9
Typical small aero-modeler-based two-stroke UAV 0.6-0.9

IC ENGINE 5
gasoline engines
Typical small aero-modeler-based four-stroke UAV
gasoline engines
0.85-1.15
Napier sabre 7 (2030 hp at 2900rmp) 2.31
Question 3.
Given data:
No of cylinders N = 5
Four- stroke engine, k =2
N= 2500
60
=41.667nps
Mechanical efficiency of the engine, n much =0.62
Indicated work per cycle, w =1000 J
=1KJ
The volume of the cylinder, Vc =3.5 L.
= 3.5 × 10-3 m3
a) Indicated mean effective pressure in kPa
IMEP= W
Vc
= 1 KJ
3.5× 10−3

IC ENGINE 6
=285.714kpa
Therefore, the indicated mean effective pressure is 285.714 kPa
b) Brake mean effective pressure in kPa.
BMEP = mechanical efficiency W
Vc
= 0.62 ×1 KJ
3.5× 10−3 M 3
= 177.142 kPa
Therefore the break mean effective pressure is 177.142 kPa.
c) Friction mean effective pressure in kPa.
FMEP = 1MEP –BMEP
=285.714 -177.142
=108.572 kPa
Therefore, the function mean effective pressure is 108.572 kPa.
d) Brake power in kW and hp.
P = mechanical efficiency WnN
K

IC ENGINE 7
0.62× 1 KJ ×5 ×( 41.667
5 )
2
=129.16/2
=64.58
Therefore, the brake power is 64 .58
P= 64.58 KW × (1.34102hp/1KW)
P= 86.6hp
Therefore the brake power in, hp is 86.6 hp.
e) Torque in N-m.
T= P
W
P
2 πN
64.58
2× π × 41.667
=0.24667KNm
Therefore, the Torque is 246.67 Nm
Question 4
a) The power output of the engine in kW and hp.

IC ENGINE 8
The generator efficiency= electrical power output
mechanical power input = 0.87
Mechanical power input = engine power output = 11924
0.87
Engine power output = (P) =13705.75 watt
Therefore p =13.706 KN
P= (13.706) (1.341) HP
P = 18.379 HP.
b) Engine torque.
Engine torque = T
Engine power output = P = 2 πNT
60
13.706 = ( 2 π ) ( 1200 ) (T )
60
Engine torque = (T) =109.07 NM
c) Engine bmep in kPa.
Engine torque (T) = ( bmep ) ( displacvement volume )
2 π

IC ENGINE 9
109.07 = ( bmep ) ( 3.1× 10−3 m3
cycle )
( 2 π )
Therefore bmep =221.06 kPa.
References.
Lumley, J. L. (2015). Engines: An Introduction. London: Cambridge University Press.