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Technical Paper

Study on Combustion Chamber Geometry Effects in an HCCI Engine Using High-Speed Cycle-Resolved Chemiluminescence Imaging

2007-04-16
2007-01-0217
The aim of this study is to see how geometry generated turbulence affects the Rate of Heat Release (ROHR) in an HCCI engine. HCCI combustion is limited in load due to high peak pressures and too fast combustion. If the speed of combustion can be decreased the load range can be extended. Therefore two different combustion chamber geometries were investigated, one with a disc shape and one with a square bowl in piston. The later one provokes squish-generated gas flow into the bowl causing turbulence. The disc shaped combustion chamber was used as a reference case. Combustion duration and ROHR were studied using heat release analysis. A Scania D12 Diesel engine, converted to port injected HCCI with ethanol was used for the experiments. An engine speed of 1200 rpm was applied throughout the tests. The effect of air/fuel ratio and combustion phasing was also studied.
Technical Paper

The Effect of Swirl on Spark Assisted Compression Ignition (SACI)

2007-07-23
2007-01-1856
Auto ignition with SI compression ratio can be achieved by retaining hot residuals, replacing some of the fresh charge. In this experimental work it is achieved by running with a negative valve overlap (NVO) trapping hot residuals. The experimental engine is equipped with a pneumatic valve train making it possible to change valve lift, phasing and duration, as well as running with valve deactivation. This makes it possible to start in SI mode, and then by increasing the NVO, thus raising the initial charge temperature it is possible to investigate the intermediate domain between SI and HCCI. The engine is then running in spark assisted HCCI mode, or spark assisted compression ignition (SACI) mode that is an acronym that describes the combustion on the borderline between SI and HCCI. In this study the effect of changing the in-cylinder flow pattern by increased swirl is studied. This is achieved by deactivating one of the two intake valves.
Technical Paper

The Effect of Piston Topland Geometry on Emissions of Unburned Hydrocarbons from a Homogeneous Charge Compression Ignition (HCCI) Engine

2001-05-07
2001-01-1893
The effect of crevice volumes on the emissions of unburned hydrocarbons from a Homogeneous Charge Compression Ignition (HCCI) engine has been experimentally investigated. By varying the size and the geometry of the largest crevice, the piston topland, it was possible to ascertain whether or not crevices are the largest source of HC. Additionally, information on quenching distances for ultra lean mixtures was obtained. The tests were performed on a single cylinder engine fuelled with iso-octane. The results showed that most of the unburned hydrocarbons descend from the crevices. Increasing the topland width to some degree lead to an increase in HC. A further increase in topland width (>1.3 mm) resulted in a reduction of HC when using mixtures richer than λ ≈ 2.8, indicating that some of the mixture trapped in the topland participates in the combustion. In conditions when combustion occurred in the topland, the HC was rather insensitive to the height of the topland.
Technical Paper

A Turbo Charged Dual Fuel HCCI Engine

2001-05-07
2001-01-1896
A 6-cylinder truck engine is modified for turbo charged dual fuel Homogeneous Charge Compression Ignition (HCCI) engine operation. Two different fuels, ethanol and n-heptane, are used to control the ignition timing. The objective of this study is to demonstrate high load operation of a full size HCCI engine and to discuss some of the typical constraints associated with HCCI operation. This study proves the possibility to achieve high loads, up to 16 bar Brake Mean Effective Pressure (BMEP), and ultra low NOx emissions, using turbo charging and dual fuel. Although the system shows great potential, it is obvious that the lack of inlet air pre heating is a drawback at low loads, where combustion efficiency suffers. At high loads, the low exhaust temperature provides little energy for turbo charging, thus causing pump losses higher than for a comparable diesel engine. Design of turbo charger therefore, is a key issue in order to achieve high loads in combination with high efficiency.
Technical Paper

Experimental and Simulated Results Detailing the Sensitivity of Natural Gas HCCI Engines to Fuel Composition

2001-09-24
2001-01-3609
Natural gas quality, in terms of the volume fraction of higher hydrocarbons, strongly affects the auto-ignition characteristics of the air-fuel mixture, the engine performance and its controllability. The influence of natural gas composition on engine operation has been investigated both experimentally and through chemical kinetic based cycle simulation. A range of two component gas mixtures has been tested with methane as the base fuel. The equivalence ratio (0.3), the compression ratio (19.8), and the engine speed (1000 rpm) were held constant in order to isolate the impact of fuel autoignition chemistry. For each fuel mixture, the start of combustion was phased near top dead center (TDC) and then the inlet mixture temperature was reduced. These experimental results have been utilized as a source of data for the validation of a chemical kinetic based full-cycle simulation.
Technical Paper

Extinction Measurements of In-Cylinder Soot Deposition in a Heavy-Duty DI Diesel Engine

2001-03-05
2001-01-1296
The combustion process in diesel engines deposits soot on the in-cylinder surfaces. Previous works have suggested that these soot deposits eventually break off during cylinder blow-down and the exhaust stroke and contribute significantly to exhaust soot emissions. In order to better understand this potential pathway to soot emissions, the authors recently investigated combusting fuel-jet/wall interactions in a diesel engine. This work, published as a companion paper, showed how soot escaped from the combusting fuel jet and was brought in close proximity to the wall so that it could become a deposit. The current study extends this earlier work with laser-extinction measurements of the soot-deposition rate in the same single-cylinder, heavy-duty DI diesel engine. Measurements were made by passing the beam of a CW-diode laser through a window in the piston bowl rim that was in-line with one of the fuel jets.
Technical Paper

Diffusion-Flame / Wall Interactions in a Heavy-Duty DI Diesel Engine

2001-03-05
2001-01-1295
Over the past decade, laser diagnostics have improved our understanding of many aspects of diesel combustion. However, interactions between the combusting fuel jet and the piston-bowl wall are not well understood. In heavy-duty diesel engines, with typical fuels, these interactions occur with the combusting vapor-phase region of the jet, which consists of a central region containing soot and other products of rich-premixed combustion, surrounded by a diffusion flame. Since previous work has shown that the OH radical is a good marker of the diffusion flame, planar laser-induced fluorescence (PLIF) imaging of OH was applied to an investigation of the diffusion flame during wall interaction. In addition, simultaneous OH PLIF and planar laser-induced incandescence (PLII) soot imaging was applied to investigate the likelihood for soot deposition on the bowl wall.
Technical Paper

The Effect of Combustion Chamber Geometry on HCCI Operation

2002-03-04
2002-01-0425
The effect of the combustion chamber geometry and the turbulence on Homogeneous Charge Compression Ignition (HCCI) operation has been experimentally investigated. A high turbulent square bowl in piston combustion chamber has been compared with a low turbulent disc combustion chamber. The results showed that the combustion chamber geometry plays large role for HCCI combustion. At the same operating conditions, the peak combustion rate for the square bowl combustion chamber was much lower compared to the disc combustion chamber. The combustion duration was in some cases almost a factor two longer for the square bowl combustion chamber. The lower combustion rate with the square bowl was due larger heat losses, lower combustion efficiency and higher turbulence.
Technical Paper

Improving Ion Current Feedback for HCCI Engine Control

2007-10-29
2007-01-4053
In HCCI you do not have the same control of the combustion like in SI and Diesel engines. Controlling the start of a combustion event is a difficult task and requires feedback from previous cycles. This feedback can be retrieved from ion current measurements. By applying a voltage over the spark gap, ions will lead a current and a signal that represents the combustion in the cylinder will be retrieved. Voltages of 450 V were used. The paper describes a new method to enhance the combustion phasing from the Ion current trace in HCCI engines. The method is using the knowledge of how the signal should look. This is known due to the fact that the shape of the ion current signal is similar from cycle to cycle. This new observation is shown in the paper. Also the correlation between the ion current and CA50 was studied. Later the signals have been used for combustion feedback.
Technical Paper

Fuel Stratification for Low-Load HCCI Combustion: Performance & Fuel-PLIF Measurements

2007-10-29
2007-01-4130
Fuel stratification has been investigated as a means of improving the low-load combustion efficiency in an HCCI engine. Several stratification techniques were examined: different GDI injectors, increased swirl, and changes in injection pressure, to determine which parameters are effective for improving the combustion efficiency while maintaining NOx emissions below U.S. 2010 limits. Performance and emission measurements were obtained in an all-metal engine. Corresponding fuel distribution measurements were made with fuel PLIF imaging in a matching optically accessible engine. The fuel used was iso-octane, which is a good surrogate for gasoline. For an idle fueling rate (ϕ = 0.12), combustion efficiency was improved substantially, from 64% to 89% at the NOx limit, using delayed fuel injection with a hollow-cone injector at an injection pressure of 120 bar.
Technical Paper

Particle Image Velocimetry Flow Measurements and Heat-Release Analysis in a Cross-Flow Cylinder Head

2002-10-21
2002-01-2840
A specially designed cylinder head, enabling unthrottled operation with a standard cam-phasing mechanism, was tested in an optical single-cylinder engine. The in-cylinder flow was measured with particle image velocimetry (PIV) and the results were compared with heat release and emission measurements. The article also discusses effects of residual gas and effective compression ratio on heat-release and emissions. The special design of the cylinder head, with one inlet and one exhaust valve per camshaft, made it possible to operate the engine unthrottled at part load. Cam phasing led to late inlet valve closing, but also to increased valve overlap. The exhaust valve closing was late in the intake stroke, resulting in high amounts of residual gases. Two different camshafts were used with late inlet valve closing. One of the camshafts had shorter valve open duration on the phased exhaust cam lobe.
Technical Paper

Effects of Fuel Parameters and Diffusion Flame Lift-Off on Soot Formation in a Heavy-Duty DI Diesel Engine

2002-03-04
2002-01-0889
To better understand the factors affecting soot formation in diesel engines, in-cylinder soot and diffusion flame lift-off were measured in a heavy-duty, direct-injection diesel engine. Measurements were obtained at two operating conditions using two commercial diesel fuels and a range of oxygenated paraffinic fuel blends. A line-of-sight laser extinction diagnostic was improved and employed to measure the relative soot concentration within the jet (“jet-soot”) and the rates of soot-wall deposition on the piston bowl-rim. An OH chemiluminescence imaging technique was developed to determine the location of the diffusion flame and to measure the lift-off lengths of the diffusion flame to estimate the amount of oxygen entrainment in the diesel jets. Both the jet-soot and the rate of soot-wall deposition were found to decrease with increasing fuel oxygen-to-carbon ratio (O/C) over a wide range of O/C.
Technical Paper

A Computational Study of the Effects of Low Fuel Loading and EGR on Heat Release Rates and Combustion Limits in HCCI Engines

2002-03-04
2002-01-1309
Two fundamental aspects of HCCI engine combustion have been investigated using a single-zone model with time-varying compression and the full chemical-kinetic mechanisms for iso-octane, a representative liquid-phase fuel. This approach allows effects of the kinetics and thermodynamics to be isolated and evaluated in a well-characterized manner, providing an understanding of the selected fundamental processes. The computations were made using the CHEMKIN-III kinetic-rate code for an 1800 rpm operating condition. The study consists of two parts. First, low-load HCCI operation was investigated to determine the role of bulk-gas reactions as a source for HC and CO emissions. The computations show that as fueling is reduced to equivalence ratios of 0.15 and lower (very light load and idle), the bulk-gas reactions do not go to completion, leading to inefficient combustion and high emissions of HC and CO.
Technical Paper

Hydrogen Addition For Improved Lean Burn Capability of Slow and Fast Burning Natural Gas Combustion Chambers

2002-10-21
2002-01-2686
One way to extend the lean burn limit of a natural gas engine is by addition of hydrogen to the primary fuel. This paper presents measurements made on a one cylinder 1.6 liter natural gas engine. Two combustion chambers, one slow and one fast burning, were tested with various amounts of hydrogen (0, 5, 10 and 15 %-vol) added to natural gas. Three operating points were investigated for each combustion chamber and each hydrogen content level; idle, part load (5 bar IMEP) and 13 bar IMEP (simulated turbocharging). Air/fuel ratio was varied between stoichiometric and the lean limit. For each operating point, a range of ignition timings were tested to find maximum brake torque (MBT) and/or knock. Heat-release rate calculations were made in order to assess the influence of hydrogen addition on burn rate. Addition of hydrogen showed an increase in burn rate for both combustion chambers, resulting in more stable combustion close to the lean limit.
Technical Paper

Load Control Using Late Intake Valve Closing in a Cross Flow Cylinder Head

2001-09-24
2001-01-3554
A newly developed cross flow cylinder head has been used for comparison between throttled and unthrottled operation using late intake valve closing. Pressure measurements have been used for calculations of indicated load and heat-release. Emission measurements has also been made. A model was used for estimating the amount of residual gases resulting from the different load strategies. Unthrottled operation using late intake valve closing resulted in lower pumping losses, but also in increased amounts of residual gases, using this cylinder head. This is due to the special design, with one intake valve and one exhaust valve per camshaft. Late intake valve closing was achieved by phasing one of the camshafts, resulting in late exhaust valve closing as well. With very late phasing - i.e. low load - the effective compression ratio was reduced. This, in combination with high amount of residual gases, resulted in a very unstable combustion.
Technical Paper

Closed-Loop Control of an HCCI Engine

2001-03-05
2001-01-1031
This paper presents a strategy for closed-loop control of a multi cylinder turbo charged Homogeneous Charge Compression Ignition (HCCI) engine. A dual fuel port injection system allows control of combustion timing and load individually for each cylinder. The two fuels used are isooctane and n-heptane, which provides a wide range of autoignition properties. Cylinder pressure sensors provide feedback and information regarding combustion. The angle of 50% heat release is calculated in real time for each cycle and used for timing feedback. Inlet air preheating is used at low loads to maintain a high combustion efficiency.
Technical Paper

Overview of Techniques for Measuring Friction Using Bench Tests and Fired Engines

2000-06-19
2000-01-1780
This paper presents an overview of techniques for measuring friction using bench tests and fired engines. The test methods discussed have been developed to provide efficient, yet realistic, assessments of new component designs, materials, and lubricants for in-cylinder and overall engine applications. A Cameron-Plint Friction and Wear Tester was modified to permit ring-in-piston-groove movement by the test specimen, and used to evaluate a number of cylinder bore coatings for friction and wear performance. In a second study, it was used to evaluate the energy conserving characteristics of several engine lubricant formulations. Results were consistent with engine and vehicle testing, and were correlated with measured fuel economy performance. The Instantaneous IMEP Method for measuring in-cylinder frictional forces was extended to higher engine speeds and to modern, low-friction engine designs.
Technical Paper

The Application of Ceramic and Catalytic Coatings to Reduce the Unburned Hydrocarbon Emissions from a Homogeneous Charge Compression Ignition Engine

2000-06-19
2000-01-1833
An experimental and theoretical study of the effect of thermal barriers and catalytic coatings in a Homogeneous Charge Compression Ignition (HCCI) engine has been conducted. The main intent of the study was to investigate if a thermal barrier or catalytic coating of the wall would support the oxidation of the near-wall unburned hydrocarbons. In addition, the effect of these coatings on thermal efficiency due to changed heat transfer characteristics was investigated. The experimental setup was based on a partially coated combustion chamber. The upper part of the cylinder liner, the piston top including the top land, the valves and the cylinder head were all coated. As a thermal barrier, a coating based on plasma-sprayed Al2O3 was used. The catalytic coating was based on plasma-sprayed ZrO2 doped with Platinum. The two coatings tested were of varying thickness' of 0.15, 0.25 and 0.6 mm. The compression ratio was set to 16.75:1.
Technical Paper

Supercharged Homogeneous Charge Compression Ignition (HCCI) with Exhaust Gas Recirculation and Pilot Fuel

2000-06-19
2000-01-1835
In an attempt to extend the upper load limit for Homogeneous Charge Compression Ignition (HCCI), supercharging in combination with Exhaust Gas Recirculation (EGR) have been applied. Two different boost pressures were used, 1.1 bar and 1.5 bar. High EGR rates were used in order to reduce the combustion rate. The highest obtained IMEP was 16 bar. This was achieved with the higher boost pressure, at close to stoichiometric conditions and with approximately 50 % EGR. Natural gas was used as the main fuel. In the case with the higher boost pressure, iso-octane was used as pilot fuel, to improve the ignition properties of the mixture. This made it possible to use a lower compression ratio and thereby reducing the maximum cylinder pressure. The tests were performed on a single cylinder engine operated at low speed (1000 rpm). The test engine was equipped with a modified cylinder head, having a Variable Compression Ratio (VCR) mechanism.
Technical Paper

An Investigation of Thermal Stratification in HCCI Engines Using Chemiluminescence Imaging

2006-04-03
2006-01-1518
Chemiluminescence imaging has been applied to investigate the naturally occurring charge stratification in an HCCI engine. This stratification slows the pressure-rise rate (PRR) during combustion, making it critical to the high-load operating limit of these engines. Experiments were conducted in a single-cylinder HCCI engine modified with windows in the combustion chamber for optical access. Using this engine, chemiluminescence images were obtained from three different view angles. These included both single-shot images with intensified CCD cameras and high-speed (20kHz) sequences with an intensified CMOS video camera. The engine was fueled with iso-octane, which has been shown to be a reasonable surrogate for gasoline and exhibits only single-stage ignition at these naturally aspirated conditions. The chemiluminescence images show that the HCCI combustion is not homogeneous but has a strong turbulent structure even when the fuel and air are fully premixed prior to intake.
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