Effect of Reformer Gas on HCCI CombustionPart I: High Octane Fuels Vahid Hosseini, and M David Checkel University of Alberta, Edmonton, Canada
supported by Auto21 National Center of Excellence
SAE World Congress 2007 Detroit, MI, USA April, 16-19 (Monday April 16- Room D2-15)
2007-01-0208
Outline
Introduction
Experimental instrumentation Definitions Results and discussions
HCCI combustion timing, Dual fuel HCCI, Reformer Gas and it’s application in HCCI
Operating region, pressure trace characteristics, heat release analysis, engine operating parameters
Conclusions 2007-01-0208
Outline
Introduction
Experimental instrumentation Definitions Results and discussions
HCCI combustion timing, Dual fuel HCCI, Reformer Gas and it’s application in HCCI
Operating region, pressure trace characteristics, heat release analysis, engine operating parameters
Conclusions 2007-01-0208
Introduction
(1)
HCCI combustion engine: drawbacks
Combustion timing control Narrow operating range High emissions of HC and CO
2007-01-0208
Introduction
(1)
HCCI combustion engine: drawbacks
Combustion timing control Narrow operating range High emissions of HC and CO
2007-01-0208
Introduction
(2)
Influential parameters on HCCI combustion timing Vary the Temperature Intake temperature and pressure
Vary the Chemistry Fuel Autoignition quality
Compression ratio Air/fuel ratio* EGR (internal, external)** *O2 concentration and specific heat (k) variation •** Five effects of EGR: charge heating, dilution, heat capacity, chemical , and stratification (SAE 2001-01-3607)
2007-01-0208
Introduction
(2)
Influential parameters on HCCI combustion timing Vary the Temperature Intake temperature and pressure
Vary the Chemistry Fuel Autoignition quality
Compression ratio Air/fuel ratio* EGR (internal, external)** Dual Fuel HCCI Engine
2007-01-0208
Introduction
(3)
Examples of Dual Fuel HCCI Engine
A blend of low octane/high octane fuels is common
Iso-octane, n-Heptane (SAE 1999-01-3679) Ethanol, n-Heptane (SAE 2001-01-1896) DME, Methanol (SAE 2004-01-2993) DME, methanol syngas (SAE 2003-01-1824)
A blend of high octane fuel and hydrogen or syngas
Natural gas, hydrogen (SAE 2004-01-1972)
2007-01-0208
Introduction
(4)
Dual Fuel HCCI Engine
Advantages
Disadvantages
Possibility of cycle-by-cycle control
Carrying two fuels onboard
Wider operating window
Infrastructure
Beneficial for dual mode HCCI/SI engine 2007-01-0208
Introduction
(4)
Dual Fuel HCCI Engine
Advantages
Disadvantages
Possibility of a cycle-bycycle control
Carrying two fuels onboard
Wider operating window
Infrastructure
Beneficial for dual mode HCCI/SI engine Onboard partial reforming of base fuel to produce reformer gas (RG) for blending
2007-01-0208
Introduction
(5)
Reformer gas (RG)- Part 1
A mixture of light gases dominated by H2 and CO Can be produced onboard with a fuel processor from hydrocarbons or alcohols Various techniques: Partial oxidation Steam reforming Autothermal reforming
2007-01-0208
Introduction
(6)
Reformer gas (RG)- Part 2
Depending on technique, base fuel, catalysts, temperatures, etc … H2 concentration may vary Some other gases may present There is an efficiency loss incorporated with reforming
Autothermal reformer efficiency is 78%~84%*
*Docter and Lamm J. of Power Sources, 1999, 84, 194-200
2007-01-0208
Introduction
(7)
Application of Reformer gas in HCCI engine
Three fuel categories have been investigated
Natural gas because of industrial applications High octane fuels (PRF100, PRF80)* suitable for Gasoline / HCCI engines Low octane fuels (PRF0, PRF20)* suitable for Diesel / HCCI engines
*PRF = Primary Reference Fuel, iso-Octane/n-Heptane blend
2007-01-0208
Introduction
(7)
Application of Reformer gas in HCCI engine
Three fuel categories have been investigated
Natural gas because of industrial applications
High octane fuel (PRF100, 80), Gasoline HCCI
Preliminary results in 2006-01-3247
Current paper (2007-01-0208)
Low octane fuel (PRF0, 20) , Diesel HCCI
Associated paper (2007-01-0206)
PRF: Primary Reference Fuel
2007-01-0208
Outline
Introduction
Experimental instrumentation Definitions Results and discussions
HCCI combustion timing, Dual fuel HCCI, Reformer gas and it’s application in HCCI
Operating region, pressure trace characteristics, heat release analysis, engine operating parameters
Conclusions 2007-01-0208
Experimental Setup
(8)
Engine, Instrumentation, and operating condition
Waukesha CFR Engine
Variable compression ratio, using octane testing head but upgraded to achieve high compression ratios
Wide open throttle, natural aspiration Steady state constant speed of 700 RPM The engine was not motored Simulated RG mixture: H2 (75%) + CO (25%) Inert gases in RG compensated by more EGR Labview DAQ Engine Monitoring System Pressure measurement with 0.1 CAD resolution
2007-01-0208
Experimental Setup
(9)
Engine and Instrumentation
Port fuel injection, manual EGR control and intake heater Electrical intake heat controlled by mixture temperature at intake port, after EGR and fuel injection T
Throttle
EGR
Heater
RG
P
Fuel
Feedback to heater
Air
Constant Tmixture
P
T
T
CFR Engine
2007-01-0208
Outline
Introduction
Experimental instrumentation Definitions Results and discussions
HCCI combustion timing, Dual fuel HCCI, Reformer gas and it’s application in HCCI
Operating region, pressure trace characteristics, heat release analysis, engine operating parameters
Conclusions 2007-01-0208
Definitions
(10)
Engine operating parameters
λ was calculated based on the both fuel and reformer gas Tintake is the temperature of the mixture (air, fuel, RG, and EGR) entering cylinder & RG m RG mass fraction (%) = 100 × & RG + m & fuel m 2007-01-0208
Definitions
(11)
Example of RG replacement effect
N=700 RPM, EGR=0%, WOT, PRF100, λ=2.0 PRF100 flow rate reduction 0% 23%
RG mass fraction 0% 30%
Air flow reduction 0% 3% Energy flow reduction 0% 1%
2007-01-0208
Definitions
(12) GHRmax
heat release analysis
A single-zone heat release model using air as working fluid*
90% GHRmax Gross Heat Release (GHR)
Combustion Duration (CD)
10% GHRmax
-40
-20 CAD, aTDC
* Internal Combustion Engine Fundamentals, Heywood ** SAE 2004-01-2996
0
Start Of Combustion (SOC)
Woschni heat transfer correlation for HCCI combustion **
20
40
2007-01-0208
Outline
Introduction
Experimental instrumentation Definitions Results and discussions
HCCI combustion timing, Dual fuel HCCI, Reformer gas and it’s application in HCCI
Operating region, pressure trace characteristics, heat release analysis, engine operating parameters
Conclusions 2007-01-0208
Results
(13)
Operating regions
Operating range was limited between knock and low IMEP RG addition did not change the operating region significantly Widest operating region was PRF80 at CR= 14.4
PRF80 CR=14.4 w/o RG
2.4
2
λ
2.8
1.6
1.2
0
10
20 30 EGR (%)
40
50
2007-01-0208
Results
(13)
Operating regions
Operating range was limited between knock and low IMEP RG addition did not change the operating region significantly Widest operating region was PRF80 at CR= 14.4
PRF80 CR=14.4 w/o RG
2.4
2
λ
2.8
1.6
PRF80 CR=14.4 w RG
1.2
0
10
20 30 EGR (%)
40
50
2007-01-0208
Results 2.8
Operating regions
Operating range was limited between knock and low IMEP RG addition did not change the operating region significantly Widest operating region was PRF80 at CR= 14.4
PRF80 CR=14.4 w/o RG
2.4
2
λ
(13)
1.6
PRF100 CR=14.4 w/o RG PRF100 CR=14.4 w RG
1.2
0
10
20 30 EGR (%)
PRF80 CR=14.4 w RG 40
50
2007-01-0208
Results
(14)
Pressure Trace Characteristics
RG=0% RG=5% RG=20% RG=30%
n tio ac fr e s as as e m ncr i
40
G
PRF80 EGR=33% λ= 1.61 ± 0.03 CR=14.4
50
R
Replacing PRF base fuel with RG could significantly alter ignition timing and other combustion phenomena
cyl. pressure (bar)
60
30
-10
0
CAD, aTDC
10
20
2007-01-0208
Results
(14)
Pressure Trace Characteristics
RG=0% RG=5% RG=20% RG=30%
60
n tio ac fr e s as as e m ncr i
PRF80 EGR=33% λ= 1.61 ± 0.03 CR=14.4
40
G
50
R
cyl. pressure (bar)
Knocking cycle, PRF80 + 0% RG
30
-10
0
CAD, aTDC
10
20
2007-01-0208
Diagnosis of Pressure traces
(dP/dθ)max
Increasing RG fraction led to smoother combustion ie. lower Pmax and lower dP/dθmax
PRF80 EGR=33% λ= 1.61 ± 0.03 CR=14.4
cyl. max. pressure rate (bar/CAD)
12
(15)
Pmax
60
10
56
8
52
6
48
4
44
2
40 0
10 20 RG mass fraction (%)
cyl. max. pressure (bar)
Results
30
2007-01-0208
Results
Main heat release is retarded and peak heat release is reduced
PRF80 EGR=33% λ= 1.61 ± 0.03 CR=14.4
(16)
160 rate of apparent heat release (J/CAD)
Apparent net rate of heat release
RG=0% RG=5% RG=20% RG=30%
120
80 RG
m in ass cr fr ea ac se tio n
40
0
-10
0
CAD, aTDC
10
20
2007-01-0208
Results
Increasing RG mass fraction:
retards ignition timing prolongs combustion duration
PRF80 EGR=33% λ= 1.61 ± 0.03 CR=14.4
combustion duration (CD), (CAD)
Diagnosis of heat release
8
6 CD SOC
5
4 4
3
0 2
start of combustion (SOC), (CAD, aTDC)
(17)
-4
1 0
10
20
RG mass fraction (%)
30
2007-01-0208
Results
(18)
Increasing RG mass fraction:
increases thermal efficiency reduces combustion efficiency Mild Knock with PRF80 + 0% RG
PRF80 EGR=33% λ= 1.61 ± 0.03 CR=14.4
indicated thermal efficiency (%)
32
100
thermal efficiency combustion efficiency
30
95 28
26
combustion efficiency (%)
Efficiencies
90 0
10 20 30 RG mass fraction (%)
40
2007-01-0208
Results knocking
PRF80 EGR=33% λ= 1.61 ± 0.03 CR=14.4
∆P
3
0.2 2
1
0.1
0
∆P knock intensity (bar)
Knock pressure fluctuation intensity reduced
RMS RMS knock intensity (bar2)
4
0.3
(19)
0 0
10 20 30 RG mass fraction (%)
∆P = max( Praw − Pfiltered ) − average( Praw − Pfiltered ) 2007-01-0208
Results
(20)
Power and Cyclic variation 3
PRF80 EGR=33% λ= 1.61 ± 0.03 CR=14.4
imep COVimep
4
3 2.5 2
COVimep (%)
IMEP goes up with RG fuel fraction (improved combustion phasing)
IMEP (bar)
5
1
2
0 0
10 20 30 RG mass fraction (%)
40
2007-01-0208
Results
(21)
Emissions: CO & HC 25
15
PRF80 EGR=33% λ= 1.61 ± 0.03 CR=14.4
isHC isCO
20
10
15
5 0
isCO (g/kW-hr)
HC emissions increase less
isHC (g/kW-hr)
CO emissions go up (CO is 25% of RG)
10 20 30 RG mass fraction (%)
2007-01-0208
Results
(22)
0.1
NOx, (already low) goes down with smoother combustion
PRF80 EGR=33% λ= 1.61 ± 0.03 CR=14.4
isNOx (g/kW-hr)
Emissions: NOx
0.05
0 0
10 20 30 RG mass fraction (%)
40
2007-01-0208
Outline
Introduction
Experimental instrumentation Definitions Results and discussions
HCCI combustion timing, Dual fuel HCCI, Reformer gas and it’s application in HCCI
Operating region, pressure trace characteristics, heat release analysis, engine operating parameters
Conclusions 2007-01-0208
Conclusions: 1
(23)
Achieving proper HCCI combustion with a high octane fuel in a non-motored CFR engine is difficult due to low power of HCCI mode and high internal friction of the engine. Reformer Gas fuel replacement can be used to control HCCI combustion timing while keeping other influential parameters (λ, EGR, Tintake, CR) constant. Operating range boundaries were not shifted significantly when replacing PRF100 or 80 base fuel with Reformer Gas. 2007-01-0208
Conclusions: 2
(24)
Keeping other influential parameters constant, RG replacement of high-octane PRF fuel retarded combustion timing leading to: Improved combustion phasing Smoother combustion Lower knock intensity Higher thermal efficiency Higher HC and CO emissions Even lower NOx emissions
A modeling approach is underway to understand the retardation effect 2007-01-0208
Thank you for your attention QUESTIONS? Vahid Hosseini
[email protected]
The contribution of the Auto21 National Center of Excellence to supporting this work is gratefully acknowledged. 2007-01-0208
