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Technical Paper

Particulate Characteristics for Varying Engine Operation in a Gasoline Spark Ignited, Direct Injection Engine

2011-04-12
2011-01-1220
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.
Technical Paper

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

2014-04-01
2014-01-1299
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).
Technical Paper

Thermodynamic Benefits of Opposed-Piston Two-Stroke Engines

2011-09-13
2011-01-2216
A detailed thermodynamic analysis was performed to demonstrate the fundamental efficiency advantage of an opposed-piston two-stroke engine over a standard four-stroke engine. Three engine configurations were considered: a baseline six-cylinder four-stroke engine, a hypothetical three-cylinder opposed-piston four-stroke engine, and a three-cylinder opposed-piston two-stroke engine. The bore and stroke per piston were held constant for all engine configurations to minimize any potential differences in friction. The closed-cycle performance of the engine configurations were compared using a custom analysis tool that allowed the sources of thermal efficiency differences to be identified and quantified.
Journal Article

Analysis of Deviations from Steady State Performance During Transient Operation of a Light Duty Diesel Engine

2012-04-16
2012-01-1067
Deviations between transient and steady state operation of a modern light duty diesel engine were identified by comparing rapid load transitions to steady state tests at the same speeds and fueling rates. The validity of approximating transient performance by matching the transient charge air flow rate and intake manifold pressure at steady state was also assessed. Results indicate that for low load operation with low temperature combustion strategies, transient deviations of MAF and MAP from steady state values are small in magnitude or short in duration and have relatively little effect on transient engine performance. A new approximation accounting for variations in intake temperature and excess oxygen content of the EGR was more effective at capturing transient emissions trends, but significant differences in magnitudes remained in certain cases indicating that additional sources of variation between transient and steady state performance remain unaccounted for.
Journal Article

Experimental Investigation of Transient Response and Turbocharger Coupling for High and Low Pressure EGR Systems

2014-04-01
2014-01-1367
The transient response of an engine with both High Pressure (HP) and Low Pressure (LP) EGR loops was compared by conducting step changes in EGR fraction at a constant engine speed and load. The HP EGR loop performance was shown to be closely linked to turbocharger performance, whereas the LP EGR loop was relatively independent of turbocharger performance and vice versa. The same experiment was repeated with the variable geometry turbine vanes completely open to reduce turbocharger action and achieve similar EGR rate changes with the HP and LP EGR loops. Under these conditions, the increased loop volume of the LP EGR loop prolonged the response of intake O2 concentration following the change in air-fuel ratio. The prolonged change of intake O2 concentration caused emissions to require more time to reach steady state as well. Strong coupling between the HP EGR loop and turbochargers was again observed using a hybrid EGR strategy.
Technical Paper

Optimization of Heat Release Shape and the Connecting Rod Crank Radius Ratio for Low Engine Noise and High Thermal Efficiency of Premixed Diesel Engine Combustion

2015-04-14
2015-01-0825
Premixed diesel combustion offers the potential of high thermal efficiency and low emissions, however, because the rapid rate of pressure rise and short combustion durations are often associated with low temperature combustion processes, noise is also an issue. The reduction of combustion noise is a technical matter that needs separate attention. Engine noise research has been conducted experimentally with a premixed diesel engine and techniques for engine noise simulation have been developed. The engine employed in the research here is a supercharged, single cylinder DI diesel research engine with a high pressure common rail fuel injection system. In the experiments, the engine was operated at 1600 rpm and 2000 rpm, the engine noise was sampled by two microphones, and the sampled engine noise was averaged and analyzed by an FFT sound analyzer.
Technical Paper

Experimental Investigation into the Effects of Direct Fuel Injection During the Negative Valve Overlap Period in an Gasoline Fueled HCCI Engine

2007-04-16
2007-01-0219
A single cylinder Yamaha research engine was operated with gasoline HCCI combustion using negative valve overlap (NVO). The injection strategy for this study involved using fuel injected directly into the cylinder during the NVO period (pre-DI) along with a secondary injection either in the intake port (PI) or directly into the cylinder (DI). The effects of timing of the pre-DI injection along with the percent of fuel injected during the pre-DI injection were studied in two sets of experiments using secondary PI and DI injections in separate experiments. Results have shown that by varying the pre-DI timing and pre-DI percent the main HCCI combustion timing can be influenced as a result of varied heat release during the negative valve overlap period along with hypothesized varied degrees of reformation of the pre-DI injected fuel. In addition to varying the main combustion timing the ISFC, emissions and combustion stability are all influenced by changes in pre-DI timing and percent.
Technical Paper

A Computational Analysis of Direct Fuel Injection During the Negative Valve Overlap Period in an Iso-Octane Fueled HCCI Engine

2007-04-16
2007-01-0227
This computational study compares predictions and experimental results for the use of direct injected iso-octane fuel during the negative valve overlap (NVO) period to achieve HCCI combustion. The total fuel injection was altered in two ways. First the pre-DI percent, (the ratio of direct injected fuel during the NVO period “pre-DI” to the secondary fuel supplied at the intake manifold “PI”), was varied at a fixed pre-DI injection timing, Secondly the timing of the pre-DI injection was varied while all of the fuel was supplied during the NVO period. A multi-zone, two-dimensional CFD simulation with chemistry was performed using KIVA-3V release 2 implemented with the CHEMKIN solver. The simulations were performed during the NVO period only.
Technical Paper

Investigation of Mixing and Temperature Effects on HC/CO Emissions for Highly Dilute Low Temperature Combustion in a Light Duty Diesel Engine

2007-04-16
2007-01-0193
There is a significant global effort to study low temperature combustion (LTC) as a tool to achieve stringent emission standards with future light duty diesel engines. LTC utilizes high levels of dilution (i.e., EGR > 60% with <10%O2 in the intake charge) to reduce overall combustion temperatures and to lengthen ignition delay, This increased ignition delay provides time for fuel evaporation and reduces in-homogeneities in the reactant mixture, thus reducing NOx formation from local temperature spikes and soot formation from locally rich mixtures. However, as dilution is increased to the limits, HC and CO can significantly increase. Recent research suggests that CO emissions during LTC result from the incomplete combustion of under-mixed fuel and charge gas occurring after the premixed burn period [1, 2]1. The objective of the present work was to increase understanding of the HC/CO emission mechanisms in LTC at part-load.
Technical Paper

Modeling Iso-octane HCCI Using CFD with Multi-Zone Detailed Chemistry; Comparison to Detailed Speciation Data Over a Range of Lean Equivalence Ratios

2008-04-14
2008-01-0047
Multi-zone CFD simulations with detailed kinetics were used to model iso-octane HCCI experiments performed on a single-cylinder research engine. The modeling goals were to validate the method (multi-zone combustion modeling) and the reaction mechanism (LLNL 857 species iso-octane) by comparing model results to detailed exhaust speciation data, which was obtained with gas chromatography. The model is compared to experiments run at 1200 RPM and 1.35 bar boost pressure over an equivalence ratio range from 0.08 to 0.28. Fuel was introduced far upstream to ensure fuel and air homogeneity prior to entering the 13.8:1 compression ratio, shallow-bowl combustion chamber of this 4-stroke engine. The CFD grid incorporated a very detailed representation of the crevices, including the top-land ring crevice and head-gasket crevice. The ring crevice is resolved all the way into the ring pocket volume. The detailed grid was required to capture regions where emission species are formed and retained.
Technical Paper

Chemiluminescence Measurements of Homogeneous Charge Compression Ignition (HCCI) Combustion

2006-04-03
2006-01-1520
A spectroscopic diagnostic system was designed to study the effects of different engine parameters on the chemiluminescence characteristic of HCCI combustion. The engine parameters studied in this work were intake temperature, fuel delivery method, fueling rate (load), air-fuel ratio, and the effect of partial fuel reforming due to intake charge preheating. At each data point, a set of time-resolved spectra were obtained along with the cylinder pressure and exhaust emissions data. It was determined that different engine parameters affect the ignition timing of HCCI combustion without altering the reaction pathways of the fuel after the combustion has started. The chemiluminescence spectra of HCCI combustion appear as several distinct peaks corresponding to emission from CHO, HCHO, CH, and OH superimposed on top of a CO-O continuum. A strong correlation was found between the chemiluminescence light intensity and the rate of heat release.
Journal Article

Sources of UHC Emissions from a Light-Duty Diesel Engine Operating in a Partially Premixed Combustion Regime

2009-04-20
2009-01-1446
Sources of unburned hydrocarbon (UHC) emissions are examined for a highly dilute (10% oxygen concentration), moderately boosted (1.5 bar), low load (3.0 bar IMEP) operating condition in a single-cylinder, light-duty, optically accessible diesel engine undergoing partially-premixed low-temperature combustion (LTC). The evolution of the in-cylinder spatial distribution of UHC is observed throughout the combustion event through measurement of liquid fuel distributions via elastic light scattering, vapor and liquid fuel distributions via laser-induced fluorescence, and velocity fields via particle image velocimetry (PIV). The measurements are complemented by and contrasted with the predictions of multi-dimensional simulations employing a realistic, though reduced, chemical mechanism to describe the combustion process.
Journal Article

A Detailed Comparison of Emissions and Combustion Performance Between Optical and Metal Single-Cylinder Diesel Engines at Low Temperature Combustion Conditions

2008-04-14
2008-01-1066
A detailed comparison of cylinder pressure derived combustion performance and engine-out emissions is made between an all-metal single-cylinder light-duty diesel engine and a geometrically equivalent engine designed for optical accessibility. The metal and optically accessible single-cylinder engines have the same nominal geometry, including cylinder head, piston bowl shape and valve cutouts, bore, stroke, valve lift profiles, and fuel injection system. The bulk gas thermodynamic state near TDC and load of the two engines are closely matched by adjusting the optical engine intake mass flow and composition, intake temperature, and fueling rate for a highly dilute, low temperature combustion (LTC) operating condition with an intake O2 concentration of 9%. Subsequent start of injection (SOI) sweeps compare the emissions trends of UHC, CO, NOx, and soot, as well as ignition delay and fuel consumption.
Technical Paper

Soot Structure in a Conventional Non-Premixed Diesel Flame

2006-04-03
2006-01-0196
An analysis of the soot formation and oxidation process in a conventional direct-injection (DI) diesel flame was conducted using numerical simulations. An improved multi-step phenomenological soot model that includes particle inception, particle coagulation, surface growth and oxidation was used to describe the soot formation and oxidation process. The soot model has been implemented into the KIVA-3V code. Other model Improvements include a piston-ring crevice model, a KH/RT spray breakup model, a droplet wall impingement model, a wall-temperature heat transfer model, and the RNG k-ε turbulence model. The Shell model was used to simulate the ignition process, and a laminar-and-turbulent characteristic time combustion model was used for the post-ignition combustion process. Experimental data from a heavy-duty, Cummins N14, research DI diesel engine operated with conventional injection under low-load conditions were selected as a benchmark.
Journal Article

Detailed Unburned Hydrocarbon Investigations in a Highly-Dilute Diesel Low Temperature Combustion Regime

2009-04-20
2009-01-0928
The objective of this research is a detailed investigation of unburned hydrocarbon (UHC) in a highly-dilute diesel low temperature combustion (LTC) regime. This research concentrates on understanding the mechanisms that control the formation of UHC via experiments and simulations in a 0.48L signal-cylinder light duty engine operating at 2000 r/min and 5.5 bar IMEP with multiple injections. A multi-gas FTIR along with other gas and smoke emissions instruments are used to measure exhaust UHC species and other emissions. Controlled experiments in the single-cylinder engine are then combined with three computational tools, namely heat release analysis of measured cylinder pressure, analysis of spray trajectory with a phenomenological spray model using in-cylinder thermodynamics [1], and KIVA-3V Chemkin CFD computations recently tested at LTC conditions [2].
Journal Article

Multiple-Event Fuel Injection Investigations in a Highly-Dilute Diesel Low Temperature Combustion Regime

2009-04-20
2009-01-0925
The objective of this research is a detailed investigation of multiple injections in a highly-dilute diesel low temperature combustion (LTC) regime. This research concentrates on understanding the performance and emissions benefits of multiple injections via experiments and simulations in a 0.48L signal cylinder light-duty engine operating at 2000 r/min and 5.5 bar IMEP. Controlled experiments in the single-cylinder engine are then combined with three computational tools, namely heat release analysis of measured cylinder pressure, a phenomenological spray model using in-cylinder thermodynamics [1], and KIVA-3V Chemkin CFD computations recently tested at LTC conditions [2]. This study examines the effects of fuel split distribution, injection event timing, rail pressure, and boost pressure which are each explored within a defined operation range in LTC.
Technical Paper

Modeling of Soot Formation During DI Diesel Combustion Using a Multi-Step Phenomenological Model

1998-10-19
982463
Predictive models of soot formation during Diesel combustion are of great practical interest, particularly in light of newly proposed strict regulations on particulate emissions. A modified version of the phenomenological model of soot formation developed previously has been implemented in KIVA-II CFD code. The model includes major generic processes involved in soot formation during combustion, i.e., formation of soot precursors, formation of surface growth species, soot particle nucleation, coagulation, surface growth and oxidation. The formulation of the model within the KIVA-II is fully coupled with the mass and energy balances in the system. The model performance has been tested by comparison with the results of optical in-cylinder soot measurements in a single cylinder Cummins NH Diesel engine. The predicted soot volume fraction, number density and particle size agree reasonably well with the experimental data.
Technical Paper

Expanding the HCCI Operation With the Charge Stratification

2004-03-08
2004-01-1756
A single cylinder CFR research engine has been run in HCCI combustion mode at the rich and the lean limits of the homogeneous charge operating range. To achieve a variation of the degree of charge stratification, two GDI injectors were installed: one was used for generating a homogeneous mixture in the intake system, and the other was mounted directly into the side of the combustion chamber. At the lean limit of the operating range, stratification showed a tremendous improvement in IMEP and emissions. At the rich limit, however, the stratification was limited by the high-pressure rise rate and high CO and NOx emissions. In this experiment the location of the DI injector was in such a position that the operating range that could be investigated was limited due to liquid fuel impingement onto the piston and liner.
Technical Paper

A Computational Investigation into the Cool Flame Region in HCCI Combustion

2004-03-08
2004-01-0552
Multi-dimensional computational efforts using comprehensive and skeletal kinetics have been made to investigate the cool flame region in HCCI combustion. The work was done in parallel to an experimental study that showed the impact of the negative temperature coefficient and the cool flame on the start of combustion using different fuels, which is now the focus of the simulation work. Experiments in a single cylinder CFR research engine with n-butane and a primary reference fuel with an octane number of 70 (PRF 70) were modeled. A comparison of the pressure and heat release traces of the experimental and computational results shows the difficulties in predicting the heat release in the cool flame region. The behavior of the driving radicals for two-stage ignition is studied and is compared to the behavior for a single-ignition from the literature. Model results show that PRF 70 exhibits more pronounced cool flame heat release than n-butane.
Technical Paper

Modeling the Effects of Late Cycle Oxygen Enrichment on Diesel Engine Combustion and Emissions

2002-03-04
2002-01-1158
A multidimensional simulation of Auxiliary Gas Injection (AGI) for late cycle oxygen enrichment was exercised to assess the merits of AGI for reducing the emissions of soot from heavy duty diesel engines while not adversely affecting the NOx emissions of the engine. Here, AGI is the controlled enhancement of mixing within the diesel engine combustion chamber by high speed jets of air or another gas. The engine simulated was a Caterpillar 3401 engine. For a particular operating condition of this engine, the simulated soot emissions of the engine were reduced by 80% while not significantly affecting the engine-out NOx emissions compared to the engine operating without AGI. The effects of AGI duration, timing, and orientation are studied to confirm the window of opportunity for realizing lower engine-out soot while not increasing engine out NOx through controlled enhancement of in-cylinder mixing.
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