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Study of In-Cylinder Combustion and Multi-Cylinder Light Duty Compression Ignition Engine Performance Using Different RON Fuels at Light Load Conditions

Univ of Wisconsin-Madison-Rolf D. Reitz
Univ. of Wisconsin-Madison-Bishwadipa Das Adhikary
Published 2013-04-08 by SAE International in United States
The effects of different Research Octane Number [RON] fuels on a multi-cylinder light-duty compression ignition [CI] engine were investigated at light load conditions. Experiments were conducted on a GM 1.9L 4-cylinder diesel engine at Argonne National Laboratory, using two different fuels, i.e., 75 RON and 93 RON.Emphasis was placed on 5 bar BMEP load, 2000 rev/min engine operation using two different RON fuels, and 2 bar BMEP load operating at 1500 rev/min using 75 RON gasoline fuel. The experiments reveal difficulty in controlling combustion at low load points using the higher RON fuel. In order to explain the experimental trends, simulations were carried out using the KIVA3V-Chemkin Computational Fluid Dynamics [CFD] Code. The numerical results were validated with the experimental results and provided insights about the engine combustion characteristics at different speeds and low load conditions using different fuels. It was observed that cycle-to-cycle and cylinder-to-cylinder variability issues complicate the multi-cylinder engine operation to a significant extent. Effective compression ratios [CR] of all 4 cylinders were found to be different, which indicates the variability in…
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Modeling the Influence of Molecular Interactions on the Vaporization of Multi-component Fuel Sprays

Univ. of Wisconsin-Madison-Qi Jiao, Youngchul Ra, Rolf D. Reitz
Published 2011-04-12 by SAE International in United States
A vaporization model for realistic multi-component fuel sprays is described. The equilibrium at the interface between liquid droplets and the surrounding gas is obtained based on the UNIFAC method, which considers non-ideal molecular interactions that can greatly enhance or suppress the vaporization of the components in the system compared to predictions from ideal mixing using Raoult's Law, especially for polar fuels. The present results using the UNIFAC method are shown to be able to capture the azeotropic behaviors of polar molecule blends, such as mixtures of benzene and ethanol, benzene and iso-propanol, and ethanol and water [1]. Predicted distillation curves of mixtures of ethanol and multi-component gasoline surrogates are compared to those from experiments, and the model gives good improvements on predictions of the distillation curves for initial ethanol volume fractions ranging from 0% to 100%. The results show that the mixture tends to exhibit an azeotrope behavior which significantly influences the shape of the distillation curves, and expands the boiling point range due to the azeotrope behavior. Finally, the model is applied to spray…
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Investigation of Post-Flame Oxidation of Unburned Hydrocarbons in Small Engines

SAE International Journal of Engines

Univ. of Wisconsin-Madison-Javier Vera, Jaal Ghandhi
  • Journal Article
  • 2011-01-0141
Published 2011-04-12 by SAE International in United States
The post-flame oxidation of unburned hydrocarbons released from the ring-pack crevice was investigated for a small, air-cooled, spark-ignition utility engine. Spark timing sweeps were performed at 50, 75 and 100% load and speeds of 1800, 2400 and 3060 RPM while operating at a 12:1 air-fuel ratio, which is typical for these engines. A global HC consumption rate (GCR) was introduced based on the temporal profile of the mass released from the ring pack; the mass release after CA90 and up to the point where the remainder of the ring pack HC mass is equal to the exhaust HC level was taken as the mass oxidized, and a rate was defined based on this mass and the corresponding crank angle period over which this took place. For all conditions tested, the GCR varied with the spark timing; advanced spark timing gave higher GCR. A threshold temperature, which corresponds to the bulk gas temperature at the end of the post-oxidation process, was found to vary with operating condition, and thus a simple model based on a kinetically…
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Study of High Speed Gasoline Direct Injection Compression Ignition (GDICI) Engine Operation in the LTC Regime

SAE International Journal of Engines

Univ. of Wisconsin-Madison-Paul Loeper, Roger Krieger, David E. Foster
General Motors LLC-Russ Durrett, Venkatesh Gopalakrishnan, Alejandro Plazas, Richard Peterson, Patrick Szymkowicz
  • Journal Article
  • 2011-01-1182
Published 2011-04-12 by SAE International in United States
An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline (termed GDICI for Gasoline Direct-Injection Compression Ignition) in the low temperature combustion (LTC) regime is presented. As an aid to plan engine experiments at full load (16 bar IMEP, 2500 rev/min), exploration of operating conditions was first performed numerically employing a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion. Operation ranges of a light-duty diesel engine operating with GDICI combustion with constraints of combustion efficiency, noise level (pressure rise rate) and emissions were identified as functions of injection timings, exhaust gas recirculation rate and the fuel split ratio of double-pulse injections. Parametric variation of the operation ranges was also investigated with respect to initial gas temperature, boost pressure and injection pressure. Following the modeling, experiments were performed under the conditions suggested by the numerical results in order to confirm the feasibility of GDICI operation at full load, as…
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Particulate Characteristics for Varying Engine Operation in a Gasoline Spark Ignited, Direct Injection Engine

Univ. of Wisconsin-Madison-Carolyn Farron, Nicholas Matthias, David E. Foster, Michael Andrie, Roger Krieger
General Motors LLC-Paul Najt, Kushal Narayanaswamy, Arun Solomon
Published 2011-04-12 by SAE International in United States
The objective of this research is a detailed investigation of particulate sizing and number count from a spark-ignited, direct-injection (SIDI) engine at different operating conditions. The engine is a 549 [cc] single-cylinder, four-valve engine with a flat-top piston, fueled by Tier II EEE. A baseline engine operating condition, with a low number of particulates, was established and repeatability at this condition was ascertained. This baseline condition is specified as 2000 rpm, 320 kPa IMEP, 280 [°bTDC] end of injection (EOI), and 25 [°bTDC] ignition timing.The particle size distributions were recorded for particle sizes between 7 and 289 [nm]. The baseline particle size distribution was relatively flat, around 1E6 [dN/dlogDp], for particle diameters between 7 and 100 [nm], before dropping off to decreasing numbers at larger diameters. Distributions resulting from a matrix of different engine conditions were recorded. These varied parameters include load, air-to-fuel ratio (A/F), spark timing, injection timing, fuel rail pressure, and oil and coolant temperatures. Most conditions resulted with uni-modal type distributions usually with an increase in magnitude of particles in comparison to…
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Assessment of RNG Turbulence Modeling and the Development of a Generalized RNG Closure Model

Univ. of Wisconsin-Madison-Rolf D. Reitz
Hunan Univ.-Bao-Lin Wang, Zhiyu Han
Published 2011-04-12 by SAE International in United States
RNG k-ε closure turbulence dissipation equations are evaluated employing the CFD code KIVA-3V Release 2. The numerical evaluations start by considering simple jet flows, including incompressible air jets and compressible helium jets. The results show that the RNG closure turbulence model predicts lower jet tip penetration than the "standard" k-ε model, as well as being lower than experimental data. The reason is found to be that the turbulence kinetic energy is dissipated too slowly in the downstream region near the jet nozzle exit. In this case, the over-predicted R term in RNG model becomes a sink of dissipation in the ε-equation. As a second step, the RNG turbulence closure dissipation models are further tested in complex engine flows to compare against the measured evolution of turbulence kinetic energy, and an estimate of its dissipation rate, during both the compression and expansion processes. In this case the turbulence energy is also over-predicted, because the turbulence model is not sufficiently dissipative. To improve predictions of the current RNG turbulence model, possible optimization approaches are explored. In particular,…
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Diesel Engine Size Scaling at Medium Load without EGR

SAE International Journal of Engines

Univ. of Wisconsin-Madison-Michael J. Tess, Chang-Wook Lee, Rolf D. Reitz
  • Journal Article
  • 2011-01-1384
Published 2011-04-12 by SAE International in United States
Several diffusion combustion scaling models were experimentally tested in two geometrically similar single-cylinder diesel engines with a bore diameter ratio of 1.7. Assuming that the engines have the same in-cylinder thermodynamic conditions and equivalence ratio, the combustion models primarily change the fuel injection pressure and engine speed in order to attain similar performance and emissions. The models tested include an extended scaling model, which scales diffusion flame lift-off length and jet spray penetration; a simple scaling model, which only scales spray penetration at equal mean piston speed; and a same speed scaling model, which holds crankshaft rotational velocity constant while also scaling spray penetration.Successfully scaling diffusion combustion proved difficult to accomplish because of apparent differences that remained in the fuel-air mixing and heat transfer processes. A computational investigation revealed that the larger nozzle diameter (relative to the ideal scaled value) used in the small engine experiments caused spray-wall impingement, which altered the mixing and subsequent combustion event. Similar pressure profiles and combustion could be achieved by increasing the injection pressure of the small engine relative…
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Validation of Mesh- and Timestep- Independent Spray Models for Multi-Dimensional Engine CFD Simulation

SAE International Journal of Fuels and Lubricants

Univ. of Wisconsin-Madison-Yue Wang, Hai-Wen Ge, Rolf D. Reitz
  • Journal Article
  • 2010-01-0626
Published 2010-04-12 by SAE International in United States
Resolution of droplet-scale processes occurring within engine sprays in multi-dimensional Computational Fluid Dynamics (CFD) simulations is not possible because impractically refined numerical meshes or time steps would be required. As a result, simulations that use coarse meshes and large time steps suffer from inaccurate predictions of mass, momentum and energy transfer between the spray drops and the combustion chamber gas, or poor prediction of droplet breakup and collision and coalescence processes. Several new spray models have been proposed to address these deficiencies, including use of an unsteady gas jet model to improve momentum transfer predictions in under-resolved regions of the spray, a vapor particle model to minimize numerical diffusion effects, and a Radius of Influence drop collision model to ensure consistent collision computations on different meshes. The present work combines these models with improved KH-RT models to improve the consistency of drop breakup predictions. A modified mean collision time model is also proposed to reduce timestep dependency of droplet collision prediction. The models have been implemented into the KIVA CFD code and are demonstrated to…
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Study the DPF Regeneration at Transient Operating Conditions Using Integrated System-Level Model

Univ. of Wisconsin-Madison-Jian Gong, Christopher J. Rutland
Published 2010-04-12 by SAE International in United States
System-level models containing engine model, emission models, and aftertreatment device models have been developed. All the sub-models have been developed separately and come from a variety of different sources. A new phenomenological CO model recently has been coupled into the previous integrated model. The emission models, including PM (particulate matter), NOx, and CO are also calibrated from experimental data. Some modification has been added to improve the integrated model and accept different aftertreatment device models for future work. The objective of this work is to study the DPF (Diesel Particulate Filter) regeneration during transient operating conditions using the integrated model.The integrated system-level model is used to studying the dynamic performance between engine and aftertreatment system. In this study, the calibrated emission models are validated at transient operating conditions. Passive and active DPF regenerations are also conducted for load and speed transients to study the transient effects on regeneration. The effects of exhaust mass flow rate, and temperature on pressure drop across the DPF during regeneration are investigated.
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Model-Based Diesel HCCI Combustion Phasing Controller in Integrated System Level Modeling

Univ. of Wisconsin-Madison-Sriram Sridharan, Christopher J. Rutland
Published 2010-04-12 by SAE International in United States
This work integrated a CA10 (crank angle at 10% heat release) controller into an integrated engine, emissions and aftertreatment model platform. Two CA10 phasing targets were chosen to analyze how advancing (or retarding) the target combustion phasing (CA10) affect the formation of NO and CO. The effect of intake valve closure (IVC) timing, which is the control mechanism for maintaining the target combustion phasing, on the cylinder trapped mass, and hence the charge temperature after compression is detailed. Finally, the relation between combustion phasing and the blow-down process leading to the exhaust process is discussed. Retarding the target combustion phasing by two degrees saw a 330 K drop in compressed charge temperature and a quadrupled reduction of peak NO emitted. Peak NO₂ emission reduced three times on account of the same. However, an increase in CO emission was observed when the combustion phasing was advanced. An integrated engine, emissions and aftertreatment models platform was used for this study. A low-temperature combustion (LTC) cylinder model was linked to serve the purpose of studying homogeneous charge compression…
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