Xin Q. Diesel Engine System Design

620 Diesel engine system design

instantaneous speed reduction caused by cylinder deactivation, the vibration

and engine speed instability can become worse and the BSFC reduction can

be very little. In such a case, sometimes the BSFC can become even worse

with cylinder deactivation.

The BSFC reduction mechanisms in the deactivated cylinders are similar

or the same between the gasoline engine and the diesel engine. But the

mechanisms of pumping loss reduction in the ring cylinders are different.

In the naturally aspirated gasoline engine, the pumping loss is reduced via an

increased intake manifold pressure due to less throttling. In the turbocharged

diesel engine, the pumping loss is reduced due to the lower exhaust manifold

pressure caused by the drastically reduced engine air ow rate owing

through the given turbine area. The reduction in air ow rate is caused by

the reduced effective engine displacement as shown in equation 9.30.

Leone and Pozar (2001) found that a universal steady-state correlation of

the percentage benet of BSFC exists as a strong function of BMEP (in the

range of 0–5 bar) for different gasoline engines with cylinder deactivation.

The percentages of BSFC gains are all almost the same at the same BMEP.

They found the BSFC benet had little sensitivity to engine speed. The

average benets of fuel consumption reduction at the steady-state operation

across the speed range in the gasoline engine cylinder deactivation are

summarized below based on the reported data in the literature: 30–40%

BSFC reduction at low idle; 22% at 1 bar BMEP; 15% at 2 bar BMEP;

10% at 3 bar BMEP; 6% at 4 bar BMEP; and 0% at 5 bar BMEP. The fuel

economy improvement by cylinder deactivation in vehicle driving cycles

ranges from 6% to 15% with an average of 10%, depending on vehicle

weight, engine size, and design constraints such as NVH, gear numbers

used for deactivation, the usage of cylinder deactivation at low idle, and

the low idle time. Leone and Pozar (2001) and Sandford et al. (1998)

reported large variations in the percentage benet of BSFC for different

vehicle applications and driving cycles. The fuel economy benet varies

signicantly between different test cycles, especially between the city and

highway driving cycles. City driving usually has a greater BSFC benet

than highway driving. If the driving cycle has a large proportion of part-

load operating conditions, the BSFC benet of cylinder deactivation will

become more prominent.

Emissions and exhaust temperature in cylinder deactivation

The cylinder deactivation in the gasoline engine tends to increase brake

specic NO

x

and reduce HC and CO emissions. HC spikes exist at the

transition from the deactivation to the activation modes. Very little data

exist in the published literature about the emissions in diesel engine cylinder

deactivation. The BMEP level in cylinder deactivation in the diesel engine

Diesel-Xin-09.indd 620 5/5/11 11:59:14 AM

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621Advanced diesel valvetrain system design

is primarily limited by soot emissions when the air–fuel ratio becomes low

in the ring cylinders.

Another major benet of cylinder deactivation by VVA is the great

increase in the exhaust gas temperature for aftertreatment operation at light

loads, low idle and warm-up without signicant BSFC penalty. Cylinder

deactivation is very effective in increasing the exhaust temperature to improve

the light-off time for the catalysts such as SCR during warm-up. Although

cylinder deactivation itself is usually not sufcient to quickly light off most

aftertreatment systems, a combined means with early or late IVC timing and

retarded fuel injection timing can be used to further increase the exhaust

temperature.

9.9.3 Diesel cylinder deactivation performance

simulation

The benet of cylinder deactivation in turbocharged diesel engines has not

been published to date. Figures 9.23–9.29 present a comprehensive simulation

analysis of cylinder deactivation for a V8 heavy-duty diesel engine with high

power density. There are fourteen scenarios (S1–S14) representing different

conditions in engine load, xed geometry turbine area, wastegate opening,

valve deactivation and shut-off timing strategies, as listed in Table 9.2. In

the analysis, both the BMEP and PMEP are dened for the entire engine,

6.4L V8 engine, 500 hp rated power at 3000

rpm, 1050 ft.lb at 1400 rpm

Engine BMEP (bar)

30

25

20

15

10

5

0

500 1000 1500 2000 2500 3000 3500 4000

Engine speed (rpm)

Part load

(cylinder

deactivation

simulation

region)

Full load lug

curve

High load

region

9.23 Engine speed–load domain in cylinder deactivation analysis.

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622 Diesel engine system design

S1, 2400 rpm 360 ft.lb

S7, 2400 rpm 360 ft.lb

S8, 2400 rpm 360 ft.lb

S1, 2400 rpm 360 ft.lb

S7, 2400 rpm 360 ft.lb

S8, 2400 rpm 360 ft.lb

BMEP = 9.6 bar

–90 0 90 180 270 360 450 540 630

Crank angle (degree)

–90 0 90 180 270 360 450 540 630

Crank angle (degree)

(a) Firing cylinder (cylinder 1)

Cylinder 1 pressure (bar, absolute)Cylinder 1 pressure (bar, absolute)

150

100

50

0

10

9

8

7

6

5

4

3

2

1

0

9.24 Effect of cylinder deactivation valving strategy on cylinder

pressure.

i.e., dened as the work per cycle divided by the total engine displacement.

In the simulation, four cylinders are deactivated (i.e., the V4 operation).

A two-stage xed geometry turbine system is used in the simulation, and

there is a wastegate valve in the high-pressure (HP) stage turbine. EGR

is assumed to be zero when the xed-geometry turbine area is selected to

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623Advanced diesel valvetrain system design

deliver sufcient air–fuel ratio for both peak torque and rated power in the

V8 operation. If a certain amount of EGR is needed to reduce NO

x

, a smaller

turbine can be selected to deliver sufcient air–fuel ratio at both full load

and part load at the given required EGR rate with a resulting higher engine

delta P and BSFC than the zero-EGR case. Therefore, with an appropriate

turbine area matched with an assumed EGR rate, the cylinder deactivation

analysis conducted here is directionally valid for other EGR rates.

S1, 2400 rpm 360 ft.lb

S7, 2400 rpm 360 ft.lb

S8, 2400 rpm 360 ft.lb

S1, 2400 rpm 360 ft.lb

S7, 2400 rpm 360 ft.lb

S8, 2400 rpm 360 ft.lb

BMEP = 9.6 bar

–90 0 90 180 270 360 450 540 630

Crank angle (degree)

–90 0 90 180 270 360 450 540 630

Crank angle (degree)

(b) Deactivation cylinder (cylinder 2)

Cylinder 2 pressure (bar, absolute)

150

100

50

0

10

9

8

7

6

5

4

3

2

1

0

9.24 Continued

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Simulation of cylinder deactivation at part load and 2400 rpm

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

S1 S6 S7 S8 S9

S1 S6 S7 S8 S9 S1 S6 S7 S8 S9

S1 S6 S7 S8 S9

BSFC (lb/(hp.hr))

Peak cylinder gas pressure (psia,

maximum of all cylinders)

Peak cylinder gas pressure of

cylinder 2 (psia)

Engine A/F ratio

0.95

0.85

0.75

0.65

0.55

0.45

0.35

2500

2000

1500

1000

500

0

2500

2000

1500

1000

500

0

80

70

60

50

40

30

20

10

9.25 Investigation of cylinder deactivation strategies.

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Simulation of cylinder deactivation at part load and 2400 rpm

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

S1 S6 S7 S8 S9

S1 S6 S7 S8 S9 S1 S6 S7 S8 S9

S1 S6 S7 S8 S9

BMEP (bar) BMEP (bar)

Engine delta P (back minus

boost, mbar)

Gross pumping loss PMEP (bar)

Peak cylinder gas temperature

of cylinder 1 (°F)

Exhaust manifold gas temperature

(°F)

400

300

200

100

0

–100

–200

0

–0.5

–1

–1.5

4000

3500

3000

2500

2000

1500

1000

1400

1300

1200

1100

1000

900

800

700

600

500

400

9.25 Continued

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Simulation of cylinder deactivation at part load and 2400 rpm

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

S1 S7 S11 S13

BSFC (lb/(hp.hr))

Peak cylinder gas pressure (psia,

maximum of all cylinders)

Peak cylinder gas pressure of

cylinder 2 (psia)

Engine A/F ratio

0.85

0.75

0.65

0.55

0.45

0.35

2500

2000

1500

1000

500

0

2500

2000

1500

1000

500

0

80

70

60

50

40

30

20

10

9.26 Effect of turbine area on cylinder deactivation.

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S1 S7 S11 S13

Simulation of cylinder deactivation at part load and 2400 rpm

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

0 1 2 3 4 5 6 7 8 9 10 11

BMEP (bar)

Engine delta P (back minus

boost, mbar)

Gross pumping loss PMEP (bar)

Exhaust manifold back pressure

(bar, absolute)

Exhaust manifold gas temperature

(°F)

400

300

200

100

0

–100

–200

0

–0.1

–0.2

–0.3

–0.4

–0.5

–0.6

2.5

2

1.5

1

1400

1300

1200

1100

1000

900

800

700

600

500

400

9.26 Continued

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Simulation of cylinder deactivation at part load and 1000 rpm

Simulation of cylinder deactivation at part load and 1600 rpm

Simulation of cylinder deactivation at part load and 1400 rpm

Simulation of cylinder deactivation at part load and 2000 rpm

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

BMEP (bar)

S1 S3 S7 S8

BSFC change relative to the

BSFC of S1

BSFC change relative to the

BSFC of S1

BSFC change relative to the

BSFC of S1

BSFC change relative to the

BSFC of S1

30%

20%

10%

0%

–10%

–20%

–30%

30%

20%

10%

0%

–10%

–20%

–30%

30%

20%

10%

0%

–10%

–20%

–30%

30%

20%

10%

0%

–10%

–20%

–30%

9.27 BSFC of cylinder deactivation at different engine speeds and loads.

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Simulation of cylinder deactivation at part load and 2400 rpm

Simulation of cylinder deactivation at part load and 3000 rpm

Simulation of cylinder deactivation at part load and 2600 rpm

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

BMEP (bar)

S1 S3 S7 S8

BSFC change relative to the

BSFC of S1

BSFC change relative to the

BSFC of S1

BSFC change relative to the

BSFC of S1

30%

20%

10%

0%

–10%

–20%

–30%

30%

20%

10%

0%

–10%

–20%

–30%

30%

20%

10%

0%

–10%

–20%

–30%

9.27 Continued

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Xin Q. Diesel Engine System Design

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