Ignition- and combustion concepts for lean operated ... - gason.eu

Tagung Verbrennungsforschung in der Schweiz, 7.9.2017, ETH Zürich

Ignition- and combustion concepts for lean operated passenger car natural gas engines Patrik Soltic1, Thomas Hilfiker1 Severin Hänggi2, Richard Hutter2

Empa, Automotive Powertrain Technologies Laboratory, CH-8600 Dübendorf 2 ETH, Institute for Dynamic Systems and Control, CH-8092 Zürich 1

Funding Statement

www.gason.eu This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 652816. The Swiss part of the project was supported by the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number 15.0145-1. The opinions expressed and arguments employed herein do not necessarily reflect the official views of the Swiss Government.

Project partners in the work described here are Volkswagen Group Research, ETH LAV, ETH IDSC, Empa, Poznan University, Ricardo Software, Continental Corp.


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Content

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Introduction: Today’s CNG Tngines and their Limitations Project: Find Diesel-Like Efficiencies in a CNG Engine Description of the Engines Experimental Environment Results Conclusions


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Content

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Introduction: Today’s CNG Engines and their Limitations Project: Find Diesel-Like Efficiencies in a CNG Engine Description of the Engines Experimental Environment Results Conclusions


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Introduction: Today’s CNG Engines and their Limitations

 

Today’s modern passenger car natural gas engines are based on petrol engines, with some adaptations Typical adaptations are Increased compression ratio (due to knock resistant methane fuel)  Adapted valves/valve seats (due to missing lubrication from methane)  Increased boost pressure (to compensate the loss of volumetric efficiency)  High-temperature turbine material (due to the lack of evaporative cooling effects) 



Typical limitations are Peak pressure (100-120 bar)  Emission reduction with three-way-catalysts (λ=1 combustion) 


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Content

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Project: Find Diesel-Like Efficiencies in a CNG Engine

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Omit λ=1 combustion → lean (diesel-like) combustion Omit petrol engine peak pressure limitation → use diesel engine as a basis Investigate the effect of the ignition system / ignition energy → use the fundamentally different ignition systems Highly insulated spark plug  Prechamber in unscavenged and gas scavenged operation  Diesel pilot ignition 

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Prechamber design: using CFD (by Volkswagen, Ricardo Software and ETH LAV), the data presented here and optical experiments will lead to an updated design later in the project


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Description of the Engines Engine 1

Engine 2

Engine 3

Spark Plug Engine

Prechamber Engine

Diesel Pilot Engine

# of cylinders / valves per cylinder

4/4

4/4

4/4

Displacement [cm3]

1968

1968

1968

Bore/stroke [mm]

81 / 95.5

81 / 95.5

81 / 95.5

Compression ratio

14.5

14.5

16.5

Ignition system

Inductive

Inductive

-

Spark plugs

NGK M12 in open chamber

NGK M10 in prechamber

-

Diesel injection system

-

-

Common Rail with Piezo Injectors

Gas port fuel injectors

Bosch NGI2 (via mixer)

Bosch NGI2 (via mixer)

Bosch NGI2 (MPI)

Prechamber injectors

-

Special design

-

EGR

-

-

-

Parameter


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Engine 1: Spark Plug Engine

Gas mixer upstream of the throttle

M12 spark plug insert (instead of diesel injector)


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Engine 2: Prechamber Engine M10 spark plug

gas supply cannula

prechamber dosing valves check valve

prechamber

cylinder pressure indication sensor


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Engine 2: Prechamber Engine

prechamber gas rail mixer gas rail

wastegate turbo


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Engine 3: Diesel Pilot Engine gas rail (added) diesel rail (original config.)

VTG turbo Compression ratio, piston bowl etc. unchanged from Diesel engine


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Content

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Experimental Environment

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Dynamic engine test bench in steady-state operation Rapid prototyping ECU with closed-loop centre of combustion control (set to 8 °CA for non-knocking conditions) Two operating points discussed here low load: 1400 rpm, 50 Nm brake torque = 3.2 bar bmep  higher load: 2000 rpm, 220 Nm brake torque = 14.0 bar bmep 

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Global λ setting: from 1 … lean limit (or peak cylinder pressure limitation) Scavenged prechamber operation: model-based control of λ=1 in the prechamber at moment of ignition Diesel pilot operation: least amount of diesel possible to reach stable combustion


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Content

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Results: Brake Efficiency (lower load) GasOn operating point A (1400 rpm / 50 Nm) 35

spark plug engine prechamber engine (passive) prechamber engine (scavenged) diesel pilot engine

34 33

brake engine efficiency [%]

32 31 30 29 28 27 26 25 24 23 22 21 20 0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

Lambda [-]

   

Spark plug: best efficiency @ λ=1.5 Passive prechamber: best efficiency @ λ=1.65 Scavenged prechamber: best efficiency @ λ=1.7, stable combustion up to λ=2 Diesel Pilot: best efficiency @ λ=1.65, high amount of diesel needed at throttled low load operation, inferior efficiency to the spark ignited concepts


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Results: Brake Efficiency (higher load) GasOn operating point K (2000 rpm / 220 Nm) 46


brake engine efficiency [%]

45 44

power loss / turbocharger limit

43

- 2% bmep

42 41

- 14% bmep

40

- 9% bmep

39 38 37 0.9

- 30% bmep

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

Lambda [-]

    

Spark plug: best efficiency @ λ=1.5 Passive prechamber: best efficiency @ λ=1.7 Scavenged prechamber: best efficiency @ λ=1.7, stable combustion up to λ=2 Diesel Pilot: best efficiency @ λ=1.45 (higher λ not possible due to peak pressure limit.) Power loss at very lean combustion (turbo is not able to cover everything)


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Results: Raw NOx emissions (lower load) GasOn operating point A (1400 rpm / 50 Nm) 20


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NOx [g/kWh]

14 12 10 8 6 4 2 0 0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

Lambda [-]

 

All spark ignited concepts show similar NOx levels, scavenged prechamber shows lowest NOx (< 1 g/kWh) at best efficiency setting (λ=1.7) Diesel Pilot: higher NOx emissions


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Results: Raw NOx Emissions (higher load) GasOn operating point K (2000 rpm / 220 Nm) 20


18 16

NOx [g/kWh]

14 power loss / turbocharger limit

12 10 8 6 4 2 0 0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

Lambda [-]

  

Leaner operation leads generally to lower NOx → advantage for the concepts which are able to burn very lean Part of the NOx advantage of the prechamber concepts for this operating point comes from delayed ignition to prevent knock Lean de-NOx system is needed to for all concepts


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Results: Raw THC emissions (lower load) GasOn operating point A (1400 rpm / 50 Nm) 70

60


THC [g/kWh]

50

40

30

20

10

0 0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

Lambda [-]

 

Active & passive prechamber shows clear benefits for lean operation Diesel Pilot: higher THC emissions


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Results: Raw THC Emissions (higher load) GasOn operating point K (2000 rpm / 220 Nm) 30


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THC [g/kWh]

20

15

10 power loss / turbocharger limit

5

0 0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

Lambda [-]

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Active & passive prechamber & diesel pilot show benefits compared to conventional spark plug operation THC (methane) emissions at lean conditions are the major (yet unsolved) challenge for all concepts


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Results: Temperatur after Turbine

GasOn operating point A (1400 rpm / 50 Nm) 450

GasOn operating point K (2000 rpm / 220 Nm) 650


600

400

550

T after turbine [°C]

T after turbine [°C]


350

300

power loss / turbocharger limit

500 450 400 350 300

250 0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

250 0.9

1.0

1.1

Lambda [-]

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1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

Lambda [-]

Lean combustion leads (of course) to reduced temperatures Prechamber operation leads to lower temperatures (possible reason: high heat transfer to the prechamber & piston, les enthalpy to the exhaust gases)


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2.1

Results: Net Heat Release Operating point: 1500 rpm / 100 Nm (higher load with COC at 8°C for all concepts without knock restrictions)






Prechamber concepts & diesel pilot show considrably faster combustion than spark plug version Ignition delay for the scavenged prechamber is extremely short

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Content

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Conclusions

 Diesel engine was able to be operated in dual fuel operation with     

only small adaptations (PFI added) whereas the diesel engine had to be substancially substancially adapted for spark ignition operation Diesel pilot operation allows stable operation with small diesel quantities (≈ 1 energy-%) at higher loads Diesel quantities have to be considerably increased at lower loads / throttled operation (≈ 70 energy-% at 2 bar bmep) which leads to inferior efficiencies The spark ignited concepts show efficiencies very close to diesel pilot operation (even if the compression ratio of the spark concepts is considerably lower) Lean combustion leads to quite low NOx levels, nevertheless, NOx aftertreatment is necessary Lean combustion leads to quite high THC (methane) levels, this is the major challenge for such concepts, especially in combination with low exhaust gas temperature levels


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Thank You!


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