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Ghandhi, Jaal
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Optical Investigation of the Impact of Pilot Ratio Variations on Natural Gas Diesel Dual-Fuel Combustion

University of Wisconsin - Madison-Keith R. Dahl, Jaal Ghandhi, David Rothamer
Published 2019-04-02 by SAE International in United States
Experiments were performed on a small-bore optically accessible engine to investigate diesel pilot ignition (DPI) and reactivity controlled compression ignition (RCCI) dual-fuel combustion strategies with direct injection of natural gas and diesel. Parametric variations of pilot ratio were performed. Natural luminosity and OH chemiluminescence movies of the combustion processes were captured at 28.8 and 14.4 kHz, respectively. These data were used to create ignition maps, which aided in comparing the propagation modes of the two combustion strategies. Lower pilot ratios resulted in lower initial heat release rates, and the initial ignition sites were generally smaller and less luminous; for increased pilot ratios the initial portion of the heat release was larger, and the ignition sites were large and bright. Comparisons between diesel pilot ignition and reactivity controlled compression ignition showed differences in combustion propagation mechanisms. DPI displayed a steady combustion propagation speed with regularly sized ignition sites. These sites grow into wedges that follow the shape of the diesel jets. From there, the combustion spreads to the spaces between the wedges and fills the field…
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Pressure-Based Knock Measurement Issues

University of Wisconsin-Arsham J. Shahlari, Jaal Ghandhi
Published 2017-03-28 by SAE International in United States
Highly time resolved measurements of cylinder pressure acquired simultaneously from three transducers were used to investigate the nature of knocking combustion and to identify biases that the pressure measurements induce. It was shown by investigating the magnitude squared coherence (MSC) between the transducer signals that frequency content above approximately 40 kHz does not originate from a common source, i.e., it originates from noise sources. The major source of noise at higher frequency is the natural frequency of the transducer that is excited by the impulsive knock event; even if the natural frequency is above the sampling frequency it can affect the measurements by aliasing. The MSC analysis suggests that 40 kHz is the appropriate cutoff frequency for low-pass filtering the pressure signal. Knowing this, one can isolate the knock event from noise more accurately. Four time windows are identified for a knock event: (1) pressure rise due to flame propagation; (2) a rapid but resolved pressure rise that is ~50 µs in duration; (3) a transducer shock period that is highly contaminated by noise that…
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A Statistical Description of Knock Intensity and Its Prediction

Army Research Laboratory-Kenneth Seonguk Kim
University of Wisconsin-Jaal Ghandhi
Published 2017-03-28 by SAE International in United States
Cycle-to-cycle variation in combustion phasing and combustion rate cause knock to occur differently in every cycle. This is found to be true even if the end gas thermo-chemical time history is the same. Three cycles are shown that have matched combustion phasing, combustion rate, and time of knock onset, but have knock intensity that differs by a factor of six. Thus, the prediction of knock intensity must include a stochastic component. It is shown that there is a relationship between the maximum possible knock intensity and the unburned fuel energy at the time of knock onset. Further, for a small window of unburned energy at knock onset, the probability density function of knock intensity is self similar when scaled by the 95th percentile of the cumulative distribution, and log-normal in shape. A methodology to predict the maximum possible knock intensity based on the volumetric expansion rate of the end gas was developed, and the expansion rate was modeled based on blast wave theory, which is proportional to the energy of the initial explosion. The results…
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Effects of Fuel Chemistry and Spray Properties on Particulate Size Distributions from Dual-Fuel Combustion Strategies

SAE International Journal of Engines

University of Wisconsin-Yizhou Zhang, Jaal Ghandhi, David Rothamer
  • Journal Article
  • 2017-01-1005
Published 2017-03-28 by SAE International in United States
The effect of direct-injected fuel on particle size distributions (PSDs) of particulate matter emitted from dual-fuel combustion strategies was investigated. The PSD data were acquired from a light-duty single-cylinder diesel engine operated using conventional diesel combustion (CDC) and two diesel/natural gas dual-fuel combustion strategies. Three different direct-injection (DI) fuels (diesel, 2,6,10-trimethyldodecane, and a primary reference fuel blend) and two different injector nozzles were studied. The DI fuels were chosen to have similar energy and ignition characteristics (heat of combustion and cetane number) but different physical and chemical properties (volatility, aromatics %, viscosity, density). The two nozzles (with different orifice diameter and spray angle) allowed a wide range in DI fuel quantity for the dual-fuel combustion strategies. The results suggest that the physical and chemical properties of the DI fuel may have a strong impact on PSD distribution shape and accumulation-mode particle concentration for CDC and natural gas combustion with a diesel-pilot-injection strategy. For diesel/natural gas RCCI combustion the PSD was found to be insensitive to the DI fuel when using two-stage dilution with a volatile…
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Experimental Investigation of the Impact of In-Cylinder Pressure Oscillations on Piston Heat Transfer

SAE International Journal of Engines

U.S. Army TARDEC-Eric Gingrich
Univ of Wisconsin Madison-Daniel Janecek, Jaal Ghandhi
  • Journal Article
  • 2016-01-9044
Published 2016-10-03 by SAE International in United States
An experimental investigation was conducted to explore the impact in-cylinder pressure oscillations have on piston heat transfer. Two fast-response surface thermocouples embedded in the piston top measured transient temperature and a commercial wireless telemetry system was used to transmit thermocouple signals from the moving piston. Measurements were made in a light-duty single-cylinder research engine operated under low temperature combustion regimes including Homogeneous Charge Compression Ignition (HCCI) and Reactivity Controlled Compression Ignition (RCCI) and Conventional Diesel (CDC). The HCCI data showed a correlated trend of higher heat transfer with increased pressure oscillation strength, while the RCCI and CDC data did not. An extensive HCCI data set was acquired. The heat transfer rate - when corrected for differences in cylinder pressure and gas temperature - was found to positively correlate with increased pressure oscillations. It is important to normalize the data before drawing conclusions as the magnitude of the effect was diminished significantly by the normalization procedure.
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Investigation of the Combustion Front Structure during Homogeneous Charge Compression Ignition Combustion via Laser Rayleigh Scattering Thermometry

SAE International Journal of Engines

University of Wisconsin-Matthew Blessinger, Jaal Ghandhi
  • Journal Article
  • 2016-01-0746
Published 2016-04-05 by SAE International in United States
The combustion propagation mechanism of homogeneous charge compression ignition combustion was investigated using planar laser Rayleigh scattering thermometry, and was compared to that of spark-ignition combustion. Ethylene and dimethyl ether were chosen as the fuels for SI and HCCI experiments and have nearly constant Rayleigh scattering cross-sections through the combustion process. Beam steering at the entrance window limited the load range for HCCI conditions and confined the quantitative interpretation of the results to local regions over which an effective beam steering correction could be applied. The SI conditions showed a clear bimodal temperature behavior with a well-defined interface between reactants and products. The HCCI results showed large regions that were partially combusted, i.e., at a temperature above the reactants but below the adiabatic flame temperature. Dual-imaging experiments confirm that the burned region was progressing towards the fully burned state. This suggests that combustion is a distributed (spatially) ignition process. There were, however, a significant number of regions of the HCCI temperature field that had relatively steep temperature gradients, which could signify the presence of a…
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Experimental Investigation of Piston Heat Transfer in a Light Duty Engine Under Conventional Diesel, Homogeneous Charge Compression Ignition, and Reactivity Controlled Compression Ignition Combustion Regimes

SAE International Journal of Engines

University of Wisconsin-Eric Gingrich, Jaal Ghandhi, Rolf D. Reitz
  • Journal Article
  • 2014-01-1182
Published 2014-04-01 by SAE International in United States
An experimental study has been conducted to provide insight into heat transfer to the piston of a light-duty single-cylinder research engine under Conventional Diesel (CDC), Homogeneous Charge Compression Ignition (HCCI), and Reactivity Controlled Compression Ignition (RCCI) combustion regimes. Two fast-response surface thermocouples embedded in the piston top measured transient temperature. A commercial wireless telemetry system was used to transmit thermocouple signals from the moving piston. A detailed comparison was made between the different combustion regimes at a range of engine speed and load conditions. The closed-cycle integrated and peak heat transfer rates were found to be lower for HCCI and RCCI when compared to CDC. Under HCCI operation, the peak heat transfer rate showed sensitivity to the 50% burn location.
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Experimental and Computational Assessment of Inlet Swirl Effects on a Gasoline Compression Ignition (GCI) Light-Duty Diesel Engine

Univ. of Wisconsin-Paul Loeper, Youngchul Ra, David E. Foster, Jaal Ghandhi
Published 2014-04-01 by SAE International in United States
The light-medium load operating regime (4-8 bar net IMEP) presents many challenges for advanced low temperature combustion strategies (e.g. HCCI, PPC) in light-duty, high speed engines. In this operating regime, lean global equivalence ratios (Φ<0.4) present challenges with respect to autoignition of gasoline-like fuels. Considering this intake temperature sensitivity, the objective of this work was to investigate, both experimentally and computationally, gasoline compression ignition (GCI) combustion operating sensitivity to inlet swirl ratio (Rs) variations when using a single fuel (87-octane gasoline) in a 0.475-liter single-cylinder engine based on a production GM 1.9-liter high speed diesel engine.For the first part of this investigation, an experimental matrix was developed to determine how changing inlet swirl affected GCI operation at various fixed load and engine speed operating conditions (4 and 8 bar net IMEP; 1300 and 2000 RPM). Here, experimental results showed significant changes in CA50 due to changes in inlet swirl ratio. For example, at the 4 bar net IMEP operating condition at 1300 RPM, a reduction in swirl ratio (from 2.2 to 1.5) caused a 6…
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On the Accuracy of Dissipation Scale Measurements in IC Engines

SAE International Journal of Engines

University of Wisconsin-Michael Tess, Jaal Ghandhi
  • Journal Article
  • 2014-01-1175
Published 2014-04-01 by SAE International in United States
The effects of imaging system resolution and laser sheet thickness on the measurement of the Batchelor scale were investigated in a single-cylinder optical engine. The Batchelor scale was determined by fitting a model spectrum to the dissipation spectrum that was obtained from fuel tracer planar laser-induced fluorescence (PLIF) images of the in-cylinder scalar field. The imaging system resolution was quantified by measuring the step-response function; the scanning knife edge technique was used to measure the 10-90% clip width of the laser sheet. In these experiments, the spatial resolution varied from a native resolution of 32.0 μm to 137.4 μm, and the laser sheet thickness ranged from 108 μm to 707 μm. Thus, the overall resolution of the imaging system was made to vary by approximately a factor of four in the in-plane dimension and a factor of six in the out-of-plane dimension. The Batchelor scale was found to increase linearly with the laser sheet thickness; a beam half-width of less than six times the effective in-plane resolution was required for 10% accuracy. The in-plane spatial…
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Comparison of Particulate Size Distributions from Advanced and Conventional Combustion - Part I: CDC, HCCI, and RCCI

SAE International Journal of Engines

Univ. of Wisconsin-Yizhou Zhang, Jaal Ghandhi, David Rothamer
  • Journal Article
  • 2014-01-1296
Published 2014-04-01 by SAE International in United States
Comparison of particulate size distribution measurements from different combustion strategies was conducted with a four-stroke single-cylinder diesel engine. Measurements were performed at four different load-speed points with matched combustion phasing. Particle size distributions were measured using a scanning mobility particle sizer (SMPS). To study the influence of volatile particles, measurements were performed with and without a volatile particle remover (thermodenuder) at low and high dilution ratios. The use of a single testing platform enables quantitative comparison between combustion strategies since background sources of particulate are held constant. A large number of volatile particles were present under low dilution ratio sample conditions for most of the operating conditions. To avoid the impact of volatile particles, comparisons were made based on the high dilution ratio measurements with the thermodenuder. As anticipated, CDC had the highest particle number emissions for all operating conditions for particle sizes greater than the 23 nm PMP cutoff. Somewhat surprisingly, the RCCI data show significantly higher particle numbers than the HCCI data for all operating conditions. The higher RCCI particle number emissions indicate…
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