Ignition- and combustion concepts for lean operated ...
Transcript of Ignition- and combustion concepts for lean operated ...
Ignition- and combustion concepts for lean operated passenger car natural gas engines
Patrik Soltic1, Thomas Hilfiker1
Severin Hänggi2, Richard Hutter2
1 Empa, Automotive Powertrain Technologies Laboratory, CH-8600 Dübendorf 2 ETH, Institute for Dynamic Systems and Control, CH-8092 Zürich
Tagung Verbrennungsforschung in der Schweiz, 7.9.2017, ETH Zürich
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Funding Statement
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.
www.gason.eu
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
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
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
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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Project: Find Diesel-Like Efficiencies in a CNG Engine
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
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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Content
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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Description of the Engines
Parameter Engine 1
Spark Plug Engine
Engine 2
Prechamber Engine
Engine 3
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 - - -
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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
check valve
prechamber cylinder pressure indication sensor
prechamber dosing valves
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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
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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Experimental Environment
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
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
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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Results: Brake Efficiency (lower load)
GasOn operating point A (1400 rpm / 50 Nm)
brak
e en
gine
effi
cien
cy [
%]
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
Lambda [-]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
spark plug engine prechamber engine (passive) prechamber engine (scavenged) diesel pilot engine
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)
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)
brak
e en
gine
eff
icie
ncy
[%]
37
38
39
40
41
42
43
44
45
46
Lambda [-]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
spark plug engine prechamber engine (passive) prechamber engine (scavenged) diesel pilot engine
GasOn operating point K (2000 rpm / 220 Nm)
power loss /turbocharger limit
- 14% bmep
- 30% bmep
- 2% bmep
- 9% bmep
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Results: Raw NOx emissions (lower load)
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
GasOn operating point A (1400 rpm / 50 Nm)
NO
x [g
/kW
h]
0
2
4
6
8
10
12
14
16
18
20
Lambda [-]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
spark plug engine prechamber engine (passive) prechamber engine (scavenged) diesel pilot engine
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Results: Raw NOx Emissions (higher load)
GasOn operating point K (2000 rpm / 220 Nm)
NO
x [g
/kW
h]
0
2
4
6
8
10
12
14
16
18
20
Lambda [-]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
power loss /turbocharger limit
spark plug engine prechamber engine (passive) prechamber engine (scavenged) diesel pilot engine
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)
Active & passive prechamber shows clear benefits for lean operation Diesel Pilot: higher THC emissions
GasOn operating point A (1400 rpm / 50 Nm)
THC
[g/
kWh]
0
10
20
30
40
50
60
70
Lambda [-]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
spark plug engine prechamber engine (passive) prechamber engine (scavenged) diesel pilot engine
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Results: Raw THC Emissions (higher load)
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
GasOn operating point K (2000 rpm / 220 Nm)
THC
[g/
kWh]
0
5
10
15
20
25
30
Lambda [-]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
power loss /turbocharger limit
spark plug engine prechamber engine (passive) prechamber engine (scavenged) diesel pilot engine
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Results: Temperatur after Turbine
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)
GasOn operating point A (1400 rpm / 50 Nm)
T af
ter t
urbi
ne [
°C]
250
300
350
400
450
Lambda [-]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
spark plug engine prechamber engine (passive) prechamber engine (scavenged) diesel pilot engine
GasOn operating point K (2000 rpm / 220 Nm)
T af
ter t
urbi
ne [
°C]
250
300
350
400
450
500
550
600
650
Lambda [-]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
power loss /turbocharger limit
spark plug engine prechamber engine (passive) prechamber engine (scavenged) diesel pilot engine
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Results: Net Heat Release
Prechamber concepts & diesel pilot show considrably faster combustion than spark plug version
Ignition delay for the scavenged prechamber is extremely short
Operating point: 1500 rpm / 100 Nm (higher load with COC at 8°C for all concepts without knock restrictions)
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Content
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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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!