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Efficiency and Emissions Characteristics of Partially Premixed Dual-Fuel Combustion by Co-Direct Injection of NG and Diesel Fuel (DI2) - Part 2

Southwest Research Institute-Gary D. Neely, Radu Florea, Jason Miwa, Zainal Abidin
Published 2017-03-28 by SAE International in United States
The CO2 advantage coupled with the low NOX and PM potential of natural gas (NG) makes it well-suited for meeting future greenhouse gas (GHG) and NOX regulations for on-road medium and heavy-duty engines. However, because NG is mostly methane, reduced combustion efficiency associated with traditional NG fueling strategies can result in significant levels of methane emissions which offset the CO2 advantage due to reduced efficiency and the high global warming potential of methane. To address this issue, the unique co-direct injection capability of the Westport HPDI fuel system was leveraged to obtain a partially-premixed fuel charge by injecting NG during the compression stroke followed by diesel injection for ignition timing control. This combustion strategy, referred to as DI2, was found to improve thermal and combustion efficiencies over fumigated dual-fuel combustion modes. In addition, DI2 provided significant thermal efficiency improvement over the baseline diffusion-controlled combustion strategy (HPDI) where NG injection occurs after diesel injection. The DI2 combustion process was analyzed using 3D-CFD and indicated that additional CH4 reductions from the crevice region may be possible by…
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Efficiency and Emissions Characteristics of Partially Premixed Dual-Fuel Combustion by Co-Direct Injection of NG and Diesel Fuel (DI2)

Southwest Research Institute-Radu Florea, Gary D. Neely, Zainal Abidin, Jason Miwa
Published 2016-04-05 by SAE International in United States
For the US market, an abundant supply of natural gas (NG) coupled with recent green-house gas (GHG) regulations have spurred renewed interest in dual-fuel combustion regimes. This paper explores the potential of co-direct injection to improve the efficiency and reduce the methane emissions versus equivalent fumigated dual-fuel combustion systems. Using the Westport HPDI engine as the experimental test platform, the paper reports the results obtained using both diffusion controlled (HPDI) combustion strategy as well as a partially-premixed combustion strategy (DI2). The DI2 combustion strategy shows good promise, as it has been found to improve the engine efficiency by over two brake thermal efficiency (BTE) points (% fuel energy) compared to the diffusion controlled combustion strategy (HPDI) while at the same time reducing the engine-out methane emissions by 75% compared to an equivalent fumigated dual-fuel combustion system. Details of the DI2 combustion process were obtained using 3D-CFD simulations and suggest further improvements of the dual-fuel combustion system are possible.
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Dual Fuel Combustion Study Using 3D CFD Tool

Southwest Research Institute-Zainal Abidin, Radu Florea, Timothy Callahan
Published 2016-04-05 by SAE International in United States
The current boom in natural gas from shale formations in the United States has reduced the price of natural gas to less than the price of petroleum fuels. Thus it is attractive to convert high horsepower diesel engines that use large quantities of fuel to dual fuel operation where a portion of the diesel fuel is replaced by natural gas. The substitution is limited by emissions of unburned natural gas and severe combustion phenomena such as auto-ignition or knock of the mixture and high rates of pressure rise during the ignition and early phase combustion of the diesel and natural gas-air mixture. In this work, the combustion process for dual fuel combustion was investigated using 3D CFD. The combustion process was modeled using detailed chemistry and a simulation domain sensitivity study was conducted to investigate the combustion to CFD geometry assumptions. A baseline model capturing the onset of knock was validated against experimental data from a heavy-duty dual-fuel engine. The model was then applied to different operating conditions exhibiting varying levels of knock strength. The…
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Numerical and Experimental Characterization of the Dual-Fuel Combustion Process in an Optically Accessible Engine

Southwest Research Institute-Radu Florea
Published 2013-04-08 by SAE International in United States
The dual-fuel combustion process of ethanol and n-heptane was characterized experimentally in an optically accessible engine and numerically through a chemical kinetic 3D-CFD investigation. Previously reported formaldehyde PLIF distributions were used as a tracer of low-temperature oxidation of straight-chained hydrocarbons and the numerical results were observed to be in agreement with the experimental data.The numerical and experimental evidence suggests that a change in the speed of flame propagation is responsible for the observed behavior of the dual-fuel combustion, where the energy release duration is increased and the maximum rate of pressure rise is decreased.Further, an explanation is provided for the asymmetrical energy release profile reported in literature which has been previously attributed to an increase in the diffusion-controlled combustion phase.
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Air-Assisted Direct Injection Diesel Investigations

Southwest Research Institute-Chad Koci, Radu Florea, Sudhakar Das, Mark Walls, Stefan Simescu, Charles Roberts
Published 2013-04-08 by SAE International in United States
Enhancement of fuel/air mixing is one path towards enabling future diesel engines to increase efficiency and control emissions. Air-assist fuel injections have shown potential for low pressure applications and the current work aims to extend air-assist feasibility understanding to high pressure environments. Analyses were completed and carried out for traditional high pressure fuel-only, internal air-assist, and external air-assist fuel/air mixing processes. A combination of analytical 0-D theory and 3D CFD were used to help understand the processes and guide the design of the air-assisted setup. The internal air-assisted setup was determined to have excellent liquid fuel vaporization, but poorer fuel dispersion than the traditional high-pressure fuel injections. The external air-assist setup showed potential in enhancing the fuel/air mixing process by a reduction in local equivalence ratios, and was selected over the internal air-assisted concept for manufacturing and experimental testing.Experiments in a constant volume combustion reactor were completed using a pre-burn technique to prepare the ambient gases to diesel auto-ignition temperature ranges (+750 K). High-speed Schlieren photography and laser extinction measurements were employed to assess both…
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Impact of Biodiesel Blends on In-cylinder Soot Temperature and Concentrations in a Small-Bore Optical Diesel Engine

Wayne State University-Kan Zha, Xin Yu, Radu Florea, Marcis Jansons
Published 2012-04-16 by SAE International in United States
Biodiesel is a desirable alternative fuel for the diesel engine due to its low engine-out soot emission tendency. When blended with petroleum-based diesel fuels, soot emissions generally decrease in proportion to the volume fraction of biodiesel in the mixture. This paper presents an experimental investigation of biodiesel impact on in-cylinder soot temperature and concentrations in a single-cylinder, small-bore, optical access, compression ignition engine. While in-cylinder soot measurements have been widely performed with two-color thermometry implemented on digital cameras, their finite dynamic range limits the observation of soot due to its dramatically different radiation intensities. To expand the dynamic range of two-color measurements, this investigation utilizes three cameras. A high-speed CMOS color camera with a wide-band Bayer filter is used to obtain simultaneous measurements of soot temperature and KL factor for high intensity soot clouds within one cycle. Additionally, two intensified CCD cameras with one narrow band pass filter on each lens are simultaneously used to measure low intensity soot clouds.The three-camera, two-color thermometry technique for determination of soot temperature and concentration is applied in an…
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Comparison of In-Cylinder Soot Evolution in an Optically Accessible Engine Fueled with JP-8 and ULSD

SAE International Journal of Fuels and Lubricants

Wayne State University-Xin Yu, Kan Zha, Radu Florea, Marcis Jansons
  • Journal Article
  • 2012-01-1315
Published 2012-04-16 by SAE International in United States
Due to the single fuel concept implemented by the US military, the soot production of diesel engines fueled with JP-8 has important implications for military vehicle visual signature and survivability. This work compares in-cylinder soot formation and oxidation of JP-8 and ULSD in a small-bore, optical diesel engine. Experimental engine-out soot emission measurements are compared to crank-angle resolved two-color measurements of soot temperature and optical thickness, KL. A 3-D chemical kinetic-coupled CFD model with line of sight integration is employed in order to investigate the soot distribution in a 2-D projection associated with the imaging plane, as well as to aid in interpreting the third dimension along the optical depth which is not available within the experimental work. The study also examines the effect of volatility on soot emission characteristics by CFD simulation.With the same injection pressure and timing for both fuels considered, heat release analysis shows JP-8 has more energy release than ULSD, however two color measurements indicate JP-8 produces less in-cylinder soot throughout the cycle as well as lower engine out measurements compared…
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Ethanol/N-Heptane Dual-Fuel Partially Premixed Combustion Analysis through Formaldehyde PLIF

SAE International Journal of Engines

Wayne State University-Radu Florea, Kan Zha, Xin Yu, Marcis Jansons, Dinu Taraza, Naeim Henein
  • Journal Article
  • 2012-01-0685
Published 2012-04-16 by SAE International in United States
As a result of recent focus on the control of Low Temperature Combustion (LTC) modes, dual-fuel combustion strategies such as Reactivity Controlled Compression Ignition (RCCI) have been developed. Reactivity stratification of the auto-igniting mixture is thought to be responsible for the increase in allowable engine load compared to other LTC combustion modes such as Homogenous Charge Compression Ignition (HCCI). The current study investigates the effect of ethanol intake fuel injection on in-cylinder formaldehyde formation and stratification within an optically accessible engine operated with n-heptane direct injection using optical measurements and zero-dimensional chemical kinetic models. Images obtained by Planar Laser Induced Fluorescence (PLIF) of formaldehyde using the third harmonic of a pulsed Nd:YAG laser indicate an increase in formaldehyde heterogeneity as measured by the fluorescence signal standard deviation. The experimental observations are complemented by a discussion regarding definitions of “reactivity”.
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The Combined Effect of HCHO and C2H4 Addition on Combustion in an Optically Accessible Diesel Engine Fueled with JP-8

SAE International Journal of Engines

Wayne State University-Marcis Jansons, Radu Florea, Kan Zha, Elena Florea
  • Journal Article
  • 2011-01-1392
Published 2011-04-12 by SAE International in United States
Misfiring or partial combustion during diesel engine operation results in the production of partial oxidation products such as ethylene (C₂H₄), carbon monoxide and aldehydes, in particular formaldehyde (HCHO). These compounds remain in the cylinder as residual gases to participate in the following engine cycle. Carbon monoxide and formaldehyde have been shown to exhibit a dual nature, retarding ignition in one temperature regime, yet decreasing ignition delay periods of hydrocarbon mixtures as temperatures exceed 1000°K. Largely unknown is the synergistic effects of such species. In this work, varying amounts of C₂H₄ and HCHO are added to the intake air of a naturally aspirated optical diesel engine and their combined effect on autoignition and subsequent combustion is examined. To observe the effect of these dopants on the low-temperature heat release (LTHR), ultraviolet chemiluminescent images are recorded using intensified CCD cameras. High-speed, crank-angle-resolved visible range images are recorded to examine soot-forming tendencies in the latter stages of combustion. Chemical kinetics modeling using a detailed hydrocarbon mechanism and a JP-8 surrogate blend is applied to track the behavior of…
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The Effect of HCHO Addition on Combustion in an Optically Accessible Diesel Engine Fueled with JP-8

SAE International Journal of Fuels and Lubricants

Wayne State University-Marcis Jansons, Radu Florea, Kan Zha, Eric Gingrich
  • Journal Article
  • 2010-01-2136
Published 2010-10-25 by SAE International in United States
Under the borderline autoignition conditions experienced during cold-starting of diesel engines, the amount and composition of residual gases may play a deterministic role. Among the intermediate species produced by misfiring and partially firing cycles, formaldehyde (HCHO) is produced in significant enough amounts and is sufficiently stable to persist through the exhaust and intake strokes to kinetically affect autoignition of the following engine cycle. In this work, the effect of HCHO addition at various phases of autoignition of n-heptane-air mixtures is kinetically modeled. Results show that HCHO has a retarding effect on the earliest low-temperature heat release (LTHR) phase, largely by competition for hydroxyl (OH) radicals which inhibits fuel decomposition. Conversely, post-LTHR, the presence of HCHO accelerates the occurrence of high-temperature ignition. Experimentally, these effects are observed by high-speed imaging of combustion in an optically-accessible diesel engine run in skip-fire mode and fueled with JP-8, whose intake is doped with HCHO. The occurrence of LTHR is both retarded and reduced in magnitude, peak heat release rates are strongly attenuated and combustion efficiency decreases as intake HCHO…
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