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SAE 2014 World Congress

Tuesday, April 8

Diagnostic Development

(Session Code PFL150)

Room 410 B

9:50 a.m.

2014-01-1175

On the Accuracy of Dissipation Scale Measurements in IC Engines

Michael Tess, Jaal Ghandhi, University of Wisconsin-Madison

ABSTRACT

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 resolution of the imaging system does not need to conform to the Nyquist condition, where at least two pixels are required to measure a given turbulence length scale, when using a spectral analysis method to calculate the Batchelor scale. Rather, the turbulence length scales can be estimated with 10% accuracy at an effective resolution equal to 1.4 times the Batchelor scale. The major developments of this work are two methods to correct the measured Batchelor scale for finite resolution effects. Based on these results and guidelines, researchers can estimate the error of existing measurements in the literature and design experiments to faithfully resolve the turbulence in engine flows.

Tuesday, April 8

Combustion in Compression-Ignition Engines: Efficiency and Emissions

(Session Code: PFL221)

Room 411 A

2:40 p.m.

2014-01-1248

Effects of Temporal-Spatial Distribution of Ignition and Combustion on Thermal Efficiency and Combustion Noise in DICI Engine

Jian Huang, Zhi Wang, Martin Wissink, Rolf Reitz, Tsinghua Univ., University of Wisconsin-Madison

ABSTRACT

The effects of the temporal and spatial distributions of ignition timings of combustion zones on combustion noise in a Direct Injection Compression Ignition (DICI) engine were studied using experimental tests and numerical simulations. The experiments were performed with different fuel injection strategies on a heavy-duty diesel engine. Cylinder pressure was measured with the sampling intervals of 0.1°CA in order to resolve noise components. The simulations were performed using the KIVA-3V code with detailed chemistry to analyze the in-cylinder ignition and combustion processes. The experimental results show that optimal sequential ignition and spatial distribution of combustion zones can be realized by adopting a two-stage injection strategy in which the proportion of the pilot injection fuel and the timings of the injections can be used to control the combustion process, thus resulting in simultaneously higher thermal efficiency and lower noise emissions. Simulated results show that if a large amount of the combustion occurs near the liner walls of the combustion chamber, this significantly contributes to high amplitude pressure oscillations, which leads to heavy knock and low thermal efficiency. Therefore, a well-organized combustion process would be one in which low temperature combustion occurs in the wall regions and subsequently high temperature combustion occurs at the central regions of the chamber, resulting in higher thermal efficiency and lower noise emissions.

Wednesday, April 9

Models for CI Combustion and Emissions
(Session Code: PFL113)

Room 140 C

8:20 a.m.

2014-01-1074

A Zero-Dimensional Phenomenological Model for RCCI Combustion Using Reaction Kinetics

Johannes Ulrich Eichmeier, KIT Karlsruhe Institute of Technology; Rolf Reitz, Christopher Rutland, University of Wisconsin

ABSTRACT

Homogeneous low temperature combustion is believed to be a promising approach to resolve the conflict of goals between high efficiency and low exhaust emissions. Disadvantageously for this kind of combustion, the whole process depends on chemical kinetics and thus is hard to control. Reactivity controlled combustion can help to overcome this difficulty. In the so-called RCCI (reactivity controlled compression ignition) combustion concept a small amount of pilot diesel that is injected directly into the combustion chamber ignites a highly diluted gasoline-air mixture. As the gasoline does not ignite without the diesel, the pilot injection timing and the ratio between diesel and gasoline can be used to control the combustion process.

A phenomenological multi-zone model to predict RCCI combustion has been developed and validated against experimental and 3D-CFD data. The model captures the main physics governing ignition and combustion. The direct diesel injection is modeled using Hiroyasu's packet approach, where all packets are treated as thermodynamic zones. After the end of injection, mixture formation is modeled as a process dominated by turbulent mixing with mass transfer from zone to zone. Therefore, an algebraic turbulence model has been implemented and compared to 3D-CFD turbulence data. As RCCI combustion is kinetically controlled, heat release is solely modeled using reaction kinetics. To account for chemical reactions a reduced mechanism is used and each zone is considered as a constant volume reactor.

Wednesday, April 9

Combustion in Compression-Ignition Engines: In-Cylinder Processes
(Session Code: PFL222)

Room 411 A

9:40 a.m.

2014-01-1256

A CFD Study of Post Injection Influences on Soot Formation and Oxidation under Diesel-Like Operating Conditions

Randy Hessel, Rolf Reitz, Mark Musculus, Jacqueline O'Connor, Daniel Flowers, University of Wisconsin, Sandia National Labs., Pennsylvania State Univ., Lawrence Livermore National Labs.

ABSTRACT

One in-cylinder strategy for reducing soot emissions from diesel engines while maintaining fuel efficiency is the use of close-coupled post injections, which are small fuel injections that follow the main fuel injection after a short delay. While the in-cylinder mechanisms of diesel combustion with single injections have been studied extensively and are relatively well understood, the in-cylinder mechanisms affecting the performance and efficacy of post injections have not been clearly established. Here, experiments from a single-cylinder heavy-duty optical research engine incorporating close- coupled post injections are modeled with three dimensional (3D) computational fluid dynamics (CFD) simulations. The overall goal is to complement experimental findings with CFD results to gain more insight into the relationship between post-injections and soot.

This paper documents the first stage of CFD results for simulating and analyzing the experimental conditions. In this stage, an engineering CFD model with a two-stage soot sub-model facilitates development of new and appropriate analysis methods. The methods include new ways to visualize and quantify soot formed, soot oxidized and net soot. Parameters used to evaluate formation and oxidation, like fuel and oxygen concentrations, are also visualized and quantified to provide a deeper understanding of the in-cylinder evolution of soot.

Experiments found and CFD replicated a trend where engine-out soot first decreases, then increases with increasing postinjection duration when both the main injection duration and dwell between injections are held constant. To help understand this trend, a number of factors that influence soot formation and oxidation are analyzed, including changes in temperature, pressure, oxygen, fuel vapor and soot distributions. Fuel vapor distribution and burn rate variation appear to be dominant factors in determining whether soot increases or decreases with post injections.

The prime conclusion regarding the in-cylinder mechanism of soot reduction by post injections is that the simulations predict that short post injections increase the rate of fuel burning, thereby reducing the soot precursor species (vapor fuel) concentration, leading to lower soot formation. The model does not predict any appreciable increase in soot oxidation with a short post injection. Indeed, late in the cycle, soot oxidation with a short post injection is slower than with only the main injection because less oxygen is available for soot oxidation after combustion of the larger injected fuel mass and because there is less soot to oxidize.

Wednesday, April 9

Combustion in Compression-Ignition Engines: In-Cylinder Processes
(Session Code: PFL222)

Room 411 A

10:00 a.m.

2014-01-1258

Modeling the Ignitability of a Pilot Injection for a Diesel Primary Reference Fuel: Impact of Injection Pressure, Ambient Temperature and Fuel Mass

Federico Perini, Dipankar Sahoo, Paul Miles, Rolf Reitz, University of Wisconsin, Sandia National Labs.

ABSTRACT

In this paper, we studied the accuracy of computational modeling of the ignition of a pilot injectionin the Sandia National Laboratories (SNL) light-duty optical engine facility, using the physical properties of a cetane/iso-cetane Diesel Primary Reference Fuel (DPRF) mixture and the reaction kinetics of a well-validated mechanism for primary reference fuels. Local fuel-air equivalence ratio measurements from fuel tracer based planar laser-induced fluorescence (PLIF) experiments were used to compare the mixture formation predictions with KIVA-ERC-based simulations. The effects of variations in injection mass from 1 mg to 4 mg, in-cylinder swirl ratio, and near-TDC temperatures on non-combusting mixture preparation were analyzed, to assess the accuracy of the model in capturing average jet behavior, despite its inability to model the non-negligible jet-by-jet variations seen in the experiments. Fired simulations were able to capture well the measured ignitability trends at the different injection conditions tested, but showed some deviations in the minimum temperature needed for robust ignition, pointing out the need for further work to focus on achieving fully comprehensive modeling with detailed chemical kinetics of the DPRF58 mixture and a full engine geometry representation.

Wednesday, April 9

Multi-Dimensional Engine Modeling (Part 3 of 4)
(Session Code: PFL120)

Room 140 B

10:20 a.m.

2014-01-1113

Improved Chemical Kinetics Numerics for the Efficient Simulation of Advanced Combustion Strategies

Federico Perini, Bishwadipa Das Adhikary, Jae Hyung Lim, Xingyuan Su, Youngchul Ra, Hu Wang, Rolf Reitz, University of Wisconsin

ABSTRACT

The incorporation of detailed chemistry models in internal combustion engine simulations is becoming mandatory as local, globally lean, low-temperature combustion strategies are setting the path towards a more efficient and environmentally sustainable use of energy resources in transportation. In this paper, we assessed the computational efficiency of a recently developed sparse analytical Jacobian chemistry solver, namely ‘SpeedCHEM’, that features both direct and Krylov-subspace solution methods for maximum efficiency for both small and large mechanism sizes. The code was coupled with a high-dimensional clustering algorithm for grouping homogeneous reactors into clusters with similar states and reactivities, to speed-up the chemical kinetics solution in multi-dimensional combustion simulations. The methodology was validated within the KIVA-ERC code, and the computational efficiency of both methods was evaluated for different, challenging engine combustion modeling cases, including dual fuel, dual direct-injection and low-load, multiple-injection RCCI, direct injection gasoline compression ignition (GDICI), and HCCI engine operation using semi-detailed chemistry representations. Reaction mechanisms of practical applicability in internal combustion engine CFD simulations were used, ranging from about 50 up to about 200 species. Computational performance for both methods was observed to reduce the computational time for the chemistry solution by up to more than one order of magnitude in comparison to a traditional, dense solution approach, even when employing the same high-efficiency internal sparse algebra and analytical formulations. This confirms that consideration of detailed chemistry is not a bottleneck anymore, allowing use of larger and more refined meshes. Further research that focused on algorithms for fast and efficient advection with a large number of species is suggested.

Wednesday, April 9

RCCI Combustion
(Session Code: PFL262)

Room 414 A/B

1:00 p.m.

2014-01-1320

High Speed Dual-Fuel RCCI Combustion for High Power Output

Jae Hyung Lim, N. Ryan Walker, Sage Kokjohn, Rolf Reitz, University of Wisconsin

ABSTRACT

In recent years society's demand and interest in clean and efficient internal combustion engines has grown significantly. Several ideas have been proposed and tested to meet this demand. In particular, dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion has demonstrated high thermal efficiency, and low engine-out NOx, and soot emissions. Unlike homogeneous charge compression ignition (HCCI) combustion, which solely relies on the chemical kinetics of the fuel for ignition control, RCCI combustion has proven to provide superior combustion controllability while retaining the known benefits of low emissions and high thermal efficiency of HCCI combustion. However, in order for RCCI combustion to be adopted as a high efficiency and low engine-out emission solution, it is important to achieve high-power operation that is comparable to conventional diesel combustion (CDC).

The present study includes experimental results that show that load increase at mid-speed operation is limited by increasing peak pressure rise rates (PPRR). Accordingly, as a high power output strategy, high speed engine operation was examined. Using CFD simulations, high speed engine operation using iso-octane and n-heptane as surrogate fuels was tested in a light-duty diesel engine. Compared to mid-speed (1900 rev/min) operation, high-speed (3000 rev/min) operation was shown to allow increased combustion controllability. The increased engine speed also reduced NOx formation residence times, resulting in reduced NOx emissions. In one particular case examined the PPRR was reduced by 56% and NOx emission decreased by 24% with high-speed operation. The improved combustion controllability also enabled the use of early injection strategies, which gave more time for the direct-injected fuel to mix, thus providing low soot and CO emissions. One potential disadvantage of high-speed operation is increased frictional losses. However, the Chen-Flynn model was used to estimate friction mean effective pressure (FMEP), which increased by only 0.5 bar as the speed was changed from 1900 to 3000 rev/min. As a result, considering the corresponding dramatic increase in power output and the accompanying low emissions and combustion controllability advantages of RCCI combustion, the present study suggests that high speed operation is a very promising path to high power density operation with RCCI combustion.

Wednesday, April 9

RCCI Combustion
(Session Code: PFL262)

Room 414 A/B

1:20 p.m.

2014-01-1325

Improving the Understanding of Intake and Charge Effects for Increasing RCCI Engine Efficiency

Derek Splitter, Martin Wissink, Dan Delvescovo, Rolf Reitz, University of Wisconsin

ABSTRACT

The present experimental engine efficiency study explores the effects of intake pressure and temperature, and premixed and global equivalence ratios on gross thermal efficiency (GTE) using the reactivity controlled compression ignition (RCCI) combustion strategy. Experiments were conducted in a heavy-duty single-cylinder engine at constant net load (IMEPn) of 8.45 bar, 1300 rev/min engine speed, with 0% EGR, and a 50% mass fraction burned combustion phasing (CA50) of 0.5°CA ATDC. The engine was port fueled with E85 for the low reactivity fuel and direct injected with 3.5% 2-ethylhexyl nitrate (EHN) doped into 91 anti-knock index (AKI) gasoline for the high-reactivity fuel. The resulting reactivity of the enhanced fuel corresponds to an AKI of approximately 56 and a cetane number of approximately 28.

The engine was operated with a wide range of intake pressures and temperatures, and the ratio of low- to high-reactivity fuel was adjusted to maintain a fixed speed-phasing-load condition. This allowed for the investigation of several combinations of intake temperature, intake pressure, and charge stratification at otherwise constant thermodynamic conditions. The results show that sources of engine inefficiency compete as functions of premixed and global equivalence ratios. Losses are minimized through proper balancing of intake pressure and temperature, such that the global equivalence ratio (Φglobal) is as lean as possible without overly lean regions of the stratified charge causing an increase in incomplete combustion. The explored speed-load-phasing combination shows that losses are minimized at conditions where approximately 2/3 of the fuel is fully premixed. The results exhibit a pathway for achieving simultaneous increases in combustion and fuel efficiency through proper fuel reactivity and initial condition management.

Wednesday, April 9

RCCI Combustion
(Session Code: PFL262)

Room 414 A/B

1:40 p.m.

2014-01-1323

Experimental Investigation of Engine Speed Transient Operation in a Light Duty RCCI Engine

Reed Hanson, Rolf Reitz, University of Wisconsin

ABSTRACT

Reactivity Controlled Compression Ignition (RCCI) is an engine combustion strategy that utilizes in-cylinder fuel blending to produce low NOx and PM emissions while maintaining high thermal efficiency. The current study investigates RCCI and conventional diesel combustion (CDC) operation in a light-duty multi-cylinder engine over transient operating conditions using a high-bandwidth, transient capable engine test cell. Transient RCCI and CDC combustion and emissions results are compared over an up-speed change from 1,000 to 2,000 rev/min. and a down-speed change from 2,000 to 1,000 rev/min. at a constant 2.0 bar BMEP load.

The engine experiments consisted of in-cylinder fuel blending with port fuel-injection (PFI) of gasoline and early-cycle, direct-injection (DI) of ultra-low sulfur diesel (ULSD) for the RCCI tests and the same ULSD for the CDC tests. At the selected engine load, a step speed change was commanded and both combustion modes were compared for performance and emissions using fast response HC, NO and PM instruments. Optimized intake conditions (i.e., intake pressure, temperature and exhaust gas recirculation (EGR)) were used to explore the robustness of RCCI using real-world operating conditions. It was found that the engine was able to operate in the RCCI combustion mode using production level engine hardware with significantly lower engine-out PM and NOx emissions than CDC over the specified transient engine operating conditions.

Wednesday, April 9

Emission Control Modeling (Part 2 of 2)

Room 411 B

1:40 p.m.

2014-01-1558

Design & Evaluation of an Exhaust Filtration Analysis (EFA) System

Sandeep Viswanathan, Stephen Sakai, David Rothamer, University of Wisconsin.

ABSTRACT

The Diesel Exhaust Filtration Analysis System (DEFA) developed at the University of Wisconsin Madison was modified to perform fundamental filtration experiments using particulate matter (PM) generated by a spark-ignition direct-injection (SIDI) engine fueled with gasoline. The newly modified system, termed the Exhaust Filtration Analysis (EFA) system, enables small-scale fundamental studies of wall-flow filtration processes. A scanning mobility particle sizer (SMPS) was used to characterize running conditions with unique particle size distributions (PSDs). The SMPS and an engine exhaust particle sizer (EEPS) were used to simultaneously measure the PSD downstream of the EFA and the real-time particulate emissions from the SIDI engine, to determine the evolution of filtration efficiency during filter loading. Corrections were developed for each running condition to compare measured PSDs between the EEPS and the SMPS in the raw, as well as, filtered exhaust stream. Background losses in the EFA system (without a filter sample) were quantified for each operating condition. Several steps were taken to minimize these losses using conventional knowledge on Brownian diffusion of particulates. Results from filtration experiments for one of the engine operating conditions using cordierite filter samples showed peak initial penetration for particles with mobility diameter (Dm) of approximately 100 nm. The most penetrating particle size reduced from approximately 90 nm to 60 nm during the filtration tests. A slight increase was observed in the penetration of particles less than 50 nm in mobility diameter, potentially due to increased velocities in the filter as flow area reduces during filter loading, or due to decreasing wall area for capture of particles by diffusion. Transition to soot cake filtration was not seen during filtration of SIDI particulates. Results from previous diesel exhaust filtration experiments using wafers with similar properties showed complete transition to cake filtration over comparable loading durations.

Wednesday, April 9

Particle Emissions from Combustion Sources (Part 3 of 3)
(Session Code: PFL450)

Room 413 B

2:20 p.m.

2014-01-1607

Modeling of Equivalence Ratio Effects on Particulate Formation in a Spark-Ignition Engine under Premixed Conditions

Qi Jiao, Rolf Reitz, University of Wisconsin.

ABSTRACT

3-D Computational Fluid Dynamics (CFD) simulations have been performed to study particulate formation in a Spark-Ignition (SI) engine under premixed conditions. A semi-detailed soot model and a chemical kinetic model, including poly-aromatic hydrocarbon (PAH) formation, were coupled with a spark ignition model and the G equation flame propagation model for SI engine simulations and for predictions of soot mass and particulate number density. The simulation results for in-cylinder pressure and particle size distribution (PSDs) are compared to available experimental studies of equivalence ratio effects during premixed operation. Good predictions are observed with regard to cylinder pressure, combustion phasing and engine load. Qualitative agreements of in-cylinder particle distributions were also obtained and the results are helpful to understand particulate formation processes.

Wednesday, April 9

Alternative and Advanced Fuels (Part 1 of 2)
(Session Code: PFL330)

Room 412 A

2:40 p.m.

2014-01-1464

A Surrogate Fuel Formulation Approach for Real Transportation Fuels with Application to Multi-Dimensional Engine Simulations

Xingyuan Su, Youngchul Ra, Rolf Reitz, University of Wisconsin.

ABSTRACT

Real transportation fuels, such as gasoline and diesel, are mixtures of thousands of different hydrocarbons. For multidimensional engine applications, numerical simulations of combustion of real fuels with all of the hydrocarbon species included exceeds present computational capabilities. Consequently, surrogate fuel models are normally utilized. A good surrogate fuel model should approximate the essential physical and chemical properties of the real fuel. In this work, we present a novel methodology for the formulation of surrogate fuel models based on local optimization and sensitivity analysis technologies. Within the proposed approach, several important fuel properties are considered. Under the physical properties, we focus on volatility, density, lower heating value (LHV), and viscosity, while the chemical properties relate to the chemical composition, hydrogen to carbon (H/C) ratio, and ignition behavior. An error tolerance is assigned to each property for convergence checking. In addition, a weighting factor is given to each property indicating its individual importance among all properties considered; the overall quality of the surrogate fuel model is controlled by a weighted error tolerance. It is observed that the solver can find an accurate surrogate fuel model for a low-cetane diesel fuel with 11 iterations. Finally, to further check the fidelity of the approach, the proposed surrogate fuel model is validated using a multi-dimensional engine simulation operated under a low temperature combustion (LTC) condition against the available experimental data. The results are also compared with a conventional single component model, viz., n-tetradecane representing physical properties and n-heptane representing chemistry. The results show that the proposed surrogate fuel model can accurately predict the overall combustion process and emissions, simultaneously; while the single component model is unable to predict the combustion process and emissions in the LTC condition for the low cetane diesel fuel.

Thursday, April 10

PPC Combustion Processes Experiments

(Session Code: PFL252)

Room 414 A/B

8:00 a.m.

2014-01-1302

Extension of the Lower Load Limit of Gasoline Compression Ignition with 87 AKI Gasoline by Injection Timing and Pressure

Christopher P. Kolodziej, Stephen Ciatti, David Vuilleumier, Bishwadipa Das Adhikary, Rolf Reitz, Argonne National Lab., Univ. of California, University of Wisconsin-Madison

Abstract:

Previous work has demonstrated the capabilities of gasoline compression ignition to achieve engine loads as high as 19.5 bar BMEP with a production multi-cylinder diesel engine using gasoline with an anti-knock index (AKI) of 87. In the current study, the low load limit of the engine was investigated using the same engine hardware configurations and 87 AKI fuel that was used to achieve 19.5 bar BMEP. Single injection, “minimum fueling” style injection timing and injection pressure sweeps (where fuel injection quantity was reduced at each engine operating condition until the coefficient of variance of indicated mean effective pressure rose to 3%) found that the 87 AKI test fuel could run under stable combustion conditions down to a load of 1.5 bar BMEP at an injection timing of −30 degrees after top dead center (°aTDC) with reduced injection pressure, but still without the use of intake air heating or uncooled EGR. A 0.4% concentration (by volume) of 2-Ethylhexyl Nitrate (EHN) was added to the 87 AKI test fuel to test the effects of increased reactivity on the minimum load attainable and injection timing at which it would occur, while maintaining similar physical mixing properties. The results showed that a 0.4% EHN addition caused the minimum attainable load to be reduced to 1.3 bar BMEP at a slightly delayed injection timing of −24 °aTDC. Effects of the minimum load level, injection timing, injection pressure, and fuel reactivity on auto-ignition, combustion phasing, specific fuel consumption, and gaseous emissions are also discussed.

Thursday, April 10

PPC Combustion Processes Experiments

(Session Code: PFL252)

Room 414 A/B

8:20 a.m.

2014-01-1299

Experimental and Computational Assessment of Inlet Swirl Effects on a Gasoline Compression Ignition (GCI) Light-Duty Diesel Engine

Paul Loeper, Youngchul Ra, David Foster, Jaal Ghandhi, University of Wisconsin-Madison

Abstract:

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 CAD advancement of CA50, while increasing swirl ratio (from 2.2 to 3.5) resulted in a 2 CAD retard of CA50. This advancement in CA50 at the 1.5 swirl ratio operating point was accompanied with significant increases in NOx emissions (from 0.2 to 1.6 g/kg-fuel). Minor adjustments in injection strategy could be made to maintain NOx emissions less than 1 g/kg-fuel.

In subsequent experiments at 4 bar net IMEP, first equivalence ratio, then CA50 were matched in an effort to further isolate the effects of changing swirl ratio. In these later cases conditions allowed for a 25C reduction in the required inlet temperature at the lower swirl condition (from 77C to 52C when reducing swirl from 2.2 to 1.5). Experimental measurements were numerically simulated to help analyze the combustion behavior and emissions characteristics using a 3D-CFD code coupled with detailed chemistry. This numerical investigation quantified the thermal and mixing effects of swirl ratio variation on mixture conditions before ignition and subsequent influence on ignition timing, in-cylinder pressure profile, and emissions.

Thursday, April 10

Abnormal SI Combustion (Part 2of 2)

(Session Code: PFL213)

Room 413 A

8:40 a.m.

2014-01-1221

Modeling Investigation of Auto-ignition and Engine Knock by HO2

Jiankun Shao, Christopher Rutland, University of Wisconsin-Madison

Abstract:

Knock in a Rotax-914 engine was modeled and investigated using an improved version of the KIVA-3V code with a G-equation combustion model, together with a reduced chemical kinetics model. The ERC-PRF mechanism with 47 species and 132 reactions [1] was adopted to model the end gas auto-ignition in front of the flame front. The model was validated by a Caterpillar SI engine and a Rotax-914 engine in different operating conditions. The simulation results agree well with available experimental results. A new engineering quantified knock criterion based on chemical mechanism was then proposed. Hydroperoxyl radical (HO2) shows obvious accumulation before auto-ignition and a sudden decrease after auto-ignition. These properties are considered to be a good capability for HO2 to investigate engine knock problems. The results of engine simulations show that HO2, as a criterion based on chemical mechanism, can give more detailed information of what is happening in the process of knock and the knock propensity in non-knock case. These capabilities make HO2 a very efficient tool for future knock research.

Thursday, April 10

PPC Combustion Processes Experiments

(Session Code: PFL252)

Room 414 A/B

9:00 a.m.

2014-01-1297

Computational Investigation of Low Load Operation in a Light-Duty Gasoline Direct Injection Compression Ignition [GDICI] Engine Using Single-Injection Strategy

Bishwadipa Das Adhikary,Rolf Reitz,Stephen Ciatti, Christopher P. Kolodziej, University of Wisconsin-Madison, Argonne National Lab.

Abstract:

The use of gasoline in a compression ignition engine has been a research focus lately due to the ability of gasoline to provide more premixing, resulting in controlled emissions of the nitrogen oxides [NOx] and particulate matter. The present study assesses the reactivity of 93 RON [87AKI] gasoline in a GM 1.9L 4-cylinder diesel engine, to extend the low load limit. A single injection strategy was used in available experiments where the injection timing was varied from −42 to −9 deg ATDC, with a step-size of 3 deg. The minimum fueling level was defined in the experiments such that the coefficient of variance [COV] of indicated mean effective pressure [IMEP] was less than 3%. The study revealed that injection at −27 deg ATDC allowed a minimum load of 2 bar BMEP. Also, advancement in the start of injection [SOI] timing in the experiments caused an earlier CA50, which became retarded with further advancement in SOI timing. To help explain these behaviors, simulations were carried out using the KIVA3V CFD code coupled with a Jacobian chemistry solver, SpeedChem. Six experimental data points were considered in order to explain the CA50 trend. The results showed that at low load conditions, the IVC temperature has a significant effect on combustion phasing control. Additional computational investigations were carried out by varying the injected fuel amount, SOI timing, swirl and nozzle hole diameter to study their effects on load minimization.

Thursday, April 10

Fundamental Advances in Heat Transfer and Thermal Sciences

(Session Code PFL160)

Room 140 B

1:00p.m.

2014-01-1182

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

Eric Gingrich, Jaal Ghandhi, Rolf Reitz, University of Wisconsin-Madison

ABSTRACT

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.

Thursday, April 10

PPC Combustion Processes Modeling

(Session Code PFL251)

Room 414 A/B

1:20p.m.

2014-01-1296

Comparison of Particulate Size Distributions from Advanced and Conventional Combustion - Part I: CDC, HCCI, and RCCI

Yizhou Zhang, Jaal Ghandhi, David Rothamer, University of Wisconsin-Madison

ABSTRACT

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 that the direct-injection of fuel and non-uniformity of the in-cylinder fuel distribution may contribute to particulate generated from RCCI. Both the RCCI and HCCI results show bimodal behavior with a large number of sub-23 nm particles present, even when high-dilution is used in conjunction with the thermodenuder. Some of these particles may be volatile particles that the thermodenuder is unable to eliminate. The nature of these particles needs to be further investigated in future work.