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ORNL is managed by UT-Battelle, LLC for the US Department of
Energy
Impacts of Air-Fuel Stratification in ACI Combustion on Particulate Matter (PM) and Gaseous EmissionsMelanie Moses-DeBusk*, John M. Storey, Samuel A. Lewis Jr, R. Maggie Connatser, Scott J. Curran
National Transportation Research Center, Oak Ridge National Laboratory
2018 CLEERS Workshop
September 18-20, 2018
Ann Arbor, MI
DOE VTO Program Mangers: Gurpreet Singh, Kevin Stork & Michael Weismiller
Funding: DOE Vehicle Technology Office, Co-Optima Program
2
BackgroundU.S. Department of Energy’s Co-Optima program is working to advance the underlying science needed to develop fuel and engine technologies that will work in tandem to achieve significant efficiency gains
• Current medium and heavy duty (MD/HD) combustion research focus:
• Improve engine emissions
• Improve engine efficiency
• Advanced Compression Ignition (ACI): LTGC, GCI, GDCI
• Varies in-cylinder air-fuel stratification
• Control injection timing, number of injections and amount of fuel in each injections
• Ideal fuel properties
• Fuel economy improvement
Increasing Air-Fuel Stratification
dieselgasoline
3
Problem
Ideal fuel for ACI Combustion:
• ACI combustion needs a fuel with high volatility and reactivity
• Diesel fuel - low volatility and low resistance to autoignition (i.e. high cetane)
• Gasoline fuel - high volatility and high resistance to autoignition (i.e. high RON)
Emissions:
• Lower engine out NOx (lower peak combustion temperatures + lean operation)
• High engine out hydrocarbon emission typically observed
• Significant particulate matter (PM) emissions at hot operation
• Regulated PM emissions can be composed of more than just soot
• PM regulated based on a mass value (US EPA)
• Teflon membrane filter collection with gravimetric measurement
• ACI significant organic particulate fraction of PM
• PM collection essential for capturing all PM
• Smoke meter (FSN) and Microsoot Sensors (MSS) not sufficient
4
Challenge:
Balance: Engine Efficiency and Emissions Trade-offs
1) How does air-fuel stratification and fuel properties impact emissions?
• Sample along the ACI Air-Fuel Stratification from HCCI toward conventional diesel combustion (CDC)
2) Can we understand ACI soot formation?
• How does PM and hydrocarbon compositions change?
• Do the fuel properties impact PM?
Localized In-cylinder(a) Regions of NOx and soot formation in local
equivalence ratio (F) versus local temperature
space. NOx and soot
islands from Kitamura et al.1 are based on
chemical kinetic simulations of n-heptane. (b)
Conceptual model of mixing limited diesel
combustion illustrating the locations of NOx
and soot formation.2
1 Kitamura, et.al. Int J Engine Res2002; 3(4): 223–248.
2 Musculus, et.al. Prog Energ Combust 2013; 39(2–3): 246–283.
Dempsey, A B; Curran, S J; Wagner, R M. Int. J. Eng. Res., 2016, 17(8) 897-917.
5
Approach
ACI Engine ExperimentsGM 1.9-L multi-cylinder diesel engine
• OEM diesel pistons
(compression ratio = 16.5)
• OEM diesel fuel system with DI
injectors
• Variable geometry turbocharger with
cooled EGR
FUELS RON 70 RON 87
Reid Vapor Pressure (RVP, psi) 7.0 11.7
Distillation T50 (F) 210.5 214
Distillation T90 (F) 271.2 285
Aromatics (vol%) 15.5% 19.4%
Olefins (vol%) 0.3% 3.7%
Saturates (vol%) 84.2% 75.7%
MON 68 83
2000 rpm, 4/5 bar
DATA LABELING
6
Approach
Emission Sampling:
(~2x)
7
283°C
314°C
266°C
263°C
266°C233-239°C
ACI Gaseous Emissions
NOx (pre-DOC):
• Engine out NOx below 6ppm (0.06 g/bhp*hr) for Lt-Combustion ACI operation
• NOx emission varies across HFS air-fuel stratification
LT-Combustion
LT-Combustion
233-239°C
8
ACI Gaseous Emissions
Hydrocarbons (pre-DOC):
• Total Hydrocarbon Emissions
− FID: Non-Oxygenated (C1)
− DNPH: Aldehydes (convert to C1)
• Total hydrocarbon emissions do not correlate with Air-Fuel Stratification
• LT-combustion produces more aldehyde than non – LT Combustion for both RON 87 and RON 70 fuels
• Aldehyde productions does not directly correlate with non-oxygenated hydrocarbon production for non-LT combustion
• Combustion temperature and fuel may contribute
LT-Combustion
283°
C
314°
C
266°
C
263°
C
266°
C
233°
C
239°
C
234°
C
9
Nuclei Accumulation
Larg
e A
gglo
mer
ates
Particulate Emissions (pre-DOC)
PMP (double dilution) EEPS
• LT Combustion shows a tri-model size distribution (nuclei, accumulation and large agglomerates)
• Tri-model distribution still present at increasing air-fuel stratification
– Nuclei mode particles still present at increasing air-fuel stratification but smaller fraction of total particulate
– Increase in Accumulation mode particles blurs tri-model distinction
– Tri-model distribution still visible for RON 87 HFS (least stratification of HFS conditions)
– Greatest stratification for each fuel has no large agglomerates
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Larg
e A
gglo
mer
ates
Nuclei Accumulation
Increasing Air-Fuel Stratification
Larg
e A
gglo
mer
ates
Nuclei Accumulation
Increasing Air-Fuel Stratification
Particulate Emissions
RON 87
RON 70
11
Particulate Matter Emission
• EC/OC sampling: elemental carbon and organic carbon
• EC large fraction of total PM mass at higher air-fuel stratifications
• LT-combustion and less air-fuel stratified HFS are predominately OC
– OC not measured by traditional time-resolved exhaust monitoring: Microsoot Sensor (MSS) or Smoke Meter (FSN)
Filter Sampling (single dilution)
1212
Summary
• Total Hydrocarbon Emissions (non-oxygenated HC & aldehydes) do not correlate with Air-Fuel Stratification
• Non-oxygenated HC and Aldehydes do not trends together
• Increased hydrocarbon contributing to significant PM mass production
• NOx emission varies across HFS air-fuel stratification
• Trend in HFS NOx may be related to exhaust temp/catalyst light-off and fuel properties
• Lowest NOx and HC not at same air-fuel stratification in HFS bin
• Tri-model particle size distribution still present at increasing air-fuel stratification
• EC large fraction of total PM mass at higher air-fuel stratifications
• LT-combustion and less air-fuel stratified HFS are predominately OC