Question

A diesel engine has a compression ratio of 19. The lowest pressure of the bike is 250 kPa, the lowest
the temperature is 180 ºC and the heat supply is 1200 kJ / kg.
(a) Draw a principle image of the engine. (1p)
(b) Draw a T-s and a P-v diagram with numbered points for the cycle (1p)
(c) Set up at least one table of given input for relevant points (1p)
The table can also be filled in with additional information as needed. The numbering shall correspond to (b) and (c).
Explain your assumptions.
(d) What is the thermal efficiency of the bicycle? (2p)
(e) How big is the engine MEP?

Answer 1

The diesel engine cycle consists in 4 processes: isentropic (reversible adiabatic) compression (the ratio of volumes here is called compression ratio); constant pressure heat addition; isentropic expansion (the ratio of volumes here is called expansion ratio); and constant volume heat rejection.

	P(kPa)	V(m^3/kg)	T(K)
1	250	0.519	453
2	15423.93	0.0273	1470.956
3	15423.93	0.0496	2670.956
4	576.28	0.519	1044.2

Considering the thermodynamic fluid is air: Cp=1kJ/kgK, Cv=0.717kJ/kgK; =1.4 and M=0.029kg/mol. The values of the table were obtained as follows:

The compression ratio is equal to:

Then

From 1 to 2 adiabatic:

From 2 the 3 the heat added is equal to:

Then

Since p2=p3:

From 3 to 4 adiabatic also and V4=V1:

The heat rejected is given by:

The efficiency is:

And the MEP: