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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

*mosesmj@ornl.gov

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

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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

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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

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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.

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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

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Approach

Emission Sampling:

(~2x)

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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

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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

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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

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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)

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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