Question

analyze the performance of a gasoline engine at various loads based on data given and to determine the torque curve, power curve and performance parameters of BMEP, volumetric efficiency, and Air/fuel ratio, plotting the data vs RPM. Making three graphs: one graphing Torque and Power.

Also address t

a. How do the torque curve and power curve compare (max values @ same RPM)?

b. Is volumetric efficiency constant, or varying with RPM..what is trend?

c. Is BMEP a constant? Does it compare more with torque or power output?

Board Time	Absorber RPM-C	Torque	Barometer	Air Temp.	Air Flow	Air Flow
sec	RPM	lb-ft	PSI	F	Data	CFM
0.015	2172	53.876	14.21	64	345.86	34.59
0.030	2177	53.896	14.21	64	347.65	34.77
0.050	2180	54.011	14.21	64	342.63	34.26
0.070	2174	53.744	14.21	64	343.56	34.36
0.090	2182	53.595	14.21	64	349.31	34.93
0.110	2170	53.879	14.21	64	342.84	34.28
0.131	2174	53.754	14.21	64	344.96	34.50
0.151	2192	53.859	14.21	64	349.31	34.93
0.171	2178	53.808	14.21	64	344.01	34.40
0.188	2183	53.785	14.21	64	346.86	34.69
0.206	2182	53.872	14.21	64	344.62	34.46
0.226	2167	53.781	14.21	64	342.23	34.22
0.246	2174	53.714	14.21	64	347.26	34.73
0.266	2166	53.933	14.21	64	341.47	34.15
0.286	2160	53.659	14.21	64	343.18	34.32
0.306	2168	53.771	14.21	64	348.12	34.81
0.326	2165	54.028	14.21	64	342.30	34.23
0.340	2169	53.568	14.21	64	345.69	34.57
0.356	2175	53.612	14.21	64	346.64	34.66
0.376	2162	53.832	14.21	64	340.82	34.08
0.396	2166	53.487	14.21	64	345.96	34.60
0.416	2179	53.561	14.21	64	347.77	34.78
0.436	2166	53.490	14.21	64	342.03	34.20
0.456	2173	53.315	14.21	64	348.22	34.82
0.476	2171	53.440	14.21	64	342.23	34.22
0.492	2164	53.291	14.21	64	344.51	34.45
0.511	2171	53.183	14.21	64	346.14	34.61
0.531	2171	53.287	14.21	64	341.15	34.11
0.551	2165	52.919	14.21	64	343.62	34.36
0.571	2173	53.017	14.21	64	348.34	34.83

Answer 1

a)You are probably thinking of the formula relating power torque and rotational speed, P = T?, which would imply a linear relationship between power and torque. However the relationship is not linear because both power and torque also depend directly on the rotational speed.
For example the torque of a permanent magnet D.C. electric motor depends linearly on the rotational speed:
T = b – a?
(where b is the torque at zero rotational speed and ‘a’ is also a constant).
This is a straight line. We can now substitute this into P = T? and obtain the formula for power:
P = b? – a?^2  
Which is quadratic and clearly not the same “shape” as the torque formula. It does not depend explicitly on the torque value itself.

For an internal combustion engine, the relationship between torque and r.p.m. is more complex, but the same applies. If you could somehow devise an engine with a constant torque output the power would indeed depend linearly on r.p.m. Many engines have a near constant torque output in the middle of their rev range which approximates this condition.

b)Volumetric efficiency is the ratio of actual amount of air and fuel mixture inducted into the cylinder to the swept volume of the cylinder.

For any engine the volumetric efficiency is not constant throughout the operating range.(considering it is designed to operate in a range and not at a constant speed like gen-sets)

The volumetric efficiency is maximum in a particular range of engine speed which depends on whole lot of engine design factors which are not a part of the question.

Volumetric efficiency thus varies with engine speed and other factors. Mass of air increases because there are more number of cycles at higher speeds. Usually the volumetric efficiency of the engine is highest where it produces maximum torque.

c)BMEP:The average (mean) pressure which, if imposed on the pistons uniformly from the top to the bottom of each power stroke, would produce the measured (brake) power output.

Please note that BMEP is purely theoretical and has NOTHING to do with ACTUAL CYLINDER PRESSURES. It is simply a tool to evaluate the efficiency of a given engine at producing torque from a given displacement

BMEP=150.8*TORQUE/DISPLACMENT(FOR 4 STOKE ENGINE)

BMEP=75.4*TORQUE/DISPLACMENT(FOR 4 STOKE ENGINE)

ANOTHER FORMULA TO CALCULATE BMEP

BMEP = n * T * 2 * pi / D

where
n = no. of revs per power stroke (2 for 4 stroke)
P = Power (watts)
D = displacement (m^3)
N = revs / sec
T = torque (Nm)