79
From Figure 7.2 a, it can be seen that the discrepancy in peak rate of heat release values influences key process simulation outputs, such as cylinder pressure and
mean temperature errors: approx. 4 of the maximum values, whereas burned gas temperatures and other ROHR characteristics except the maximum rate of pressure
increase are much less affected. Regarding operating condition 5 Figure 7.2 b and 15 Figure 7.2 c, deviations between measured and simulated cylinder pres-
sures and temperatures are smaller than 1 of the maximum values, although the maximum ROHR values and the start of combustion can differ significantly e.g.
operating condition 15.
a
b
c
Fig. 7.2 Comparison of Cylinder Pressures and ROHRs left side, Burned
Gas and Mean Temperatures right side for Three Selected Heavy- Duty Diesel Operating Conditions; a 2, b 5, and c 15
R O
H R
[ °
C A
] 4
8 12
16 20
Crank Angle ϕ [° CA aTDC]
330 345
360 375
390 405
P re
ss u
re p
[b a
r] 10
20 30
40 50
60 70
80
Measurement Simulat ion
2
T e
m p
e ra
tu re
[K ]
500 1000
1500 2000
2500 3000
Crank Angle ϕ [° CA aTDC]
330 345
360 375
390 405
420
T
burn
T
mean
2
Measurement Simulat ion
P re
ss u
re p
[b a
r] 10
20 30
40 50
60 70
80
Measurement Simulat ion
R O
H R
[ °
C A
] 2
4 6
8 10
Crank Angle ϕ [° CA aTDC]
330 345
360 375
390 405
5
T e
m p
e ra
tu re
[K ]
500 1000
1500 2000
2500 3000
Crank Angle ϕ [° CA aTDC]
330 345
360 375
390 405
420
Measurement Simulat ion
T
burn
T
mean
5
R O
H R
[ °
C A
] 2
4 6
8 10
Crank Angle ϕ [° CA aTDC]
330 345
360 375
390 405
P re
ss u
re p
[b a
r]
30 40
50 60
70 80
90 100
110
Measurement Simulat ion
15
T e
m p
e ra
tu re
[K ]
500 1000
1500 2000
2500 3000
Crank Angle ϕ [° CA aTDC]
330 345
360 375
390 405
420
Measurement Simulation
T
burn
T
mean
15
80
The comparison of cylinder pressures and temperatures for representative heavy- duty engine operating conditions thus indicates, that the proposed model is able to
predict ROHRs with sufficient accuracy for use with common engine process simu- lation programs.
7.2.2 Combustion Characteristics
Common engine process simulation characteristics are used to investigate the per- formance of the model for all 19 operating conditions given. As an example,
Figure 7.3 shows measured and simulated values of maximum cylinder pressure and its location a, as well as maximum burned gas and mean temperature b.
Whereas there are only minor discrepancies noted in the maximum cylinder pres- sure, and burned gas and mean temperatures, the values for the maximum cylinder
pressure location at operating condition 9 differ by almost 13 °CA. Upon closer inspection of both the measured and simulated cylinder pressures for this operating
condition c.f. Figure 7.4, it is revealed, that the discrepancy is caused by minor dif- ferences between the two characteristic maxima
1
of the pressure histories. While the location of the maxima for the simulated pressure history is due to the late com-
bustion process at approximately 372 [°CA aTDC], it is due to cylinder compres- sionexpansion only for the measured pressure history at 360 [°CA aTDC], i.e. the
combustion process maxima is smaller than the compressionexpansion maxima..
As measures related to mechanical strains and turbocharger efficiency for exam- ple, the maximum and exhaust pressure and temperature are key factors in modern
engine RD. These engine process simulation outputs and their corresponding rel- ative errors are given in Figure 7.5 left and right side, respectively, where it can be
1. 1
st
Maxima: geometrically defined by the “compressionexpansion” transition at TDC 2
nd
Maxima: pressure increase due to late combustion SOC after TDC
a b
Fig. 7.3 Comparison of Engine Process Simulation Characteristics:
a Maximum Pressure and Location of Maximum Pressure, b Maximum Temperature and Maximum Mean Temperature
L o
c a
ti o
n M
a x
. P
re ss
u re
[° C
A a
T D
C ]
355 360
365 370
375 380
385 390
Heavy-Duty Operating Conditions [-] 2
4 6
8 10
12 14
16 18
20 M
a x
im u
m P
re ss
u re
[b a
r]
40 50
60 70
80 90
100 110
p
max
Sim Meas
ϕ
pmax
Sim Meas
M a
x im
u m
T e
m p
e ra
tu re
[K ]
2200 2300
2400 2500
2600 2700
2800
M a
x im
u m
M e
a n
T e
m p
e ra
tu re
[K ]
1400 1500
1600 1700
1800 1900
2000 2100
Heavy-Duty Operating Conditions [ -] 2
4 6
8 10
12 14
16 18
20
T
burn. max
Sim Meas T
mean. max
Sim Meas
81
seen, that the measured and simulated values are well correlated. Although errors in maximum pressure up to 12 are noted with an average error of approximately 5
or 3.5 [bar] in absolute values, deviations in the exhaust pressure are smaller than 1 with an average error of approximately 0.3 . Furthermore, errors in both the
exhaust and maximum mean temperatures are less than 5 or 30 K and 65 K in absolute values, respectively, clearly indicating the good performance of the pro-
posed ROHR model in terms of engine process characteristics.
Fig. 7.4 Comparison of Cylinder Pressures and ROHRs left side, Burn and
Mean Temperatures right side for Operating Condition 9
a
b
Fig. 7.5 Comparison of Engine Process Simulation Characteristics
left side: Absolute Values, right side: According Relative Errors: a Maximum Pressure and Maximum Mean Temperature
b Exhaust Pressure and Exhaust Temperature
R O
H R
[ °
C A
] 1
2 3
4 5
6 7
8
Crank Angle ϕ [° CA aTDC]
330 345
360 375
390 405
P re
ss u
re p
[b a
r] 10
20 30
40 50
60 70
80
Measurement Simulat ion
9
T e
m p
e ra
tu re
[K ]
500 1000
1500 2000
2500 3000
Crank Angle ϕ [° CA aTDC]
330 345
360 375
390 405
420
Measurement Simulat ion
T
burn
T
mean
9
M a
x im
u m
P re
ss u
re [b
a r]
40 50
60 70
80 90
100 110
p
max
Sim Meas T
mean. max
Sim Meas
M a
x im
u m
M e
a n
T e
m p
e ra
tu re
[K ]
1400 1500
1600 1700
1800 1900
2000 2100
Heavy-Duty Operating Conditions [ -] 2
4 6
8 10
12 14
16 18
20 E
rr o
r T
m e
a n
.m a
x
[ ]
-6 -4
-2 2
4 6
Heavy-Duty Operating Conditions [-] 2
4 6
8 10
12 14
16 18
20 E
rr o
r p
m a
x
[ ]
-15 -10
-5 5
10 15
p
max
T
mean. max
E x
h a
u st
T e
m p
e ra
tu re
[K ]
600 650
700 750
800 850
900 950
1000
Heavy-Duty Operating Conditions [ -] 2
4 6
8 10
12 14
16 18
20 E
x h
a u
st P
re ss
u re
[b a
r]
0. 9 1. 0
1. 1 1. 2
1. 3 1. 4
1. 5 1. 6
1. 7
p
exh
Sim Meas T
exh
Sim Meas
E rr
o r
p
e x
h
[ ]
-0. 8 -0. 6
-0. 4 -0. 2
0. 2 0. 4
0. 6 0. 8
p
exh
T
e xh
E rr
o r
T
e x
h
[ ]
-6 -4
-2 2
4 6
Heavy-Dut y Operat ing Condit ions [ -] 2
4 6
8 1 0
1 2 1 4
1 6 1 8
2 0
