Showing papers by "Bengt Johansson published in 2005"

Exercise intolerance in adult congenital heart disease: comparative severity, correlates, and prognostic implication.

Abstract: BACKGROUND: Although some patients with adult congenital heart disease (ACHD) report limitations in exercise capacity, we hypothesized that depressed exercise capacity may be more widespread than s ...

Operating Conditions Using Spark Assisted HCCI Combustion During Combustion Mode Transfer to SI in a Multi-Cylinder VCR-HCCI Engine

Abstract: Fuel economy improvement using combined CAI and cylinder deactivation (CDA)-an initial study p. 15 Co-evaporative tracer-PRF mixtures for LIF measurements in optical HCCI engines p. 23 Potential of thermal stratification and combustion retard for reducing pressure-rise rates in HCCI engines, based on multi-zone modeling and experiments p. 33 Analysis of premixed charge compression ignition combustion with a sequential fluid mechanics-multizone chemical kinetics model p. 49 Injection mode modulation for HCCI diesel combustion p. 61 A new reduced chemical kinetic model for autoignition and oxidation of lean n-heptane/air mixtures in HCCI engines p. 71 HCCI operation control in a multi-cylinder gasoline engine p. 85 Modeling the effects of EGR and injection pressure on soot formation in a high-speed direct-injection (HSDI) diesel engine using a multi-step phenomenological soot model p. 93 NOx and N2O formation in HCCI engines p. 115 Investigation of nano-particulate production from low temperature combustion p. 125 Optical diagnostics of laser-induced and spark plug-assisted HCCI combustion p. 135 Cylinder-to-cylinder and cycle-to-cycle variations at HCCI operation with trapped residuals p. 147 Control of HCCI during engine transients by aid of variable valve timings through the use of model based non-linear compensation p. 161 Effects of injection timing and valve timings on CAI operation in a multi-cylinder DI gasoline engine p. 177 The effects of combined internal and external exhaust gas recirculation on gasoline controlled auto-ignition p. 189 Control of CAI combustion through injection timing in a GDI engine with an air-assisted injector p. 205 Visualization and performance analysis of gasoline homogeneous charge induced ignition by diesel p. 217 Effects of spark ignition and stratified charge on gasoline HCCI combustion with direct injection p. 225 Correlation of low temperature heat release with fuel composition and HCCI engine combustion p. 237 HCCI combustion with internal fuel reforming, varied levels of EGR and charge preheat-a computational study p. 251 Investigation of mixture quality effect on CAI combustion p. 261 Numerical study of effects of fuel injection timings on CAI/HCCI combustion in a four-stroke GDI engine p. 281 Variable valve actuation for timing control of a homogeneous charge compression ignition engine p. 301 The use of variable geometry sprays with low pressure injection for optimization of diesel HCCI engine combustion p. 311 Basic research on the suitable fuel for HCCI engine from the viewpoint of chemical reaction p. 323 Load control for an HCCI engine p. 337

Lean Burn Natural Gas Operation vs. Stoichiometric Operation with EGR and a Three Way Catalyst

Abstract: Exhaust emissions from lean burn natural gas engines may not always be as low as the potential permits, especially engines with open-loop lambda control. These engines can produce much higher emissions than a comparable diesel engine without exhaust gas aftertreatment. Even if the engine has closed-loop lambda control, emissions are often unacceptably high for future emission regulations. A three-way catalyst is, today, the best way to reduce hazardous emissions. The drawback is that the engine has to operate with a stoichiometric mixture and this leads to; higher heat losses, higher pumping work at low to medium loads, higher thermal stress on the engine and higher knock tendency (requiring lower compression ratio, and thus lower brake efficiency). One way to reduce these drawbacks is to dilute the stoichiometric mixture with EGR. This paper compares lean burn operation with operation at stoichiometric conditions diluted with EGR, and using a three-way catalyst. The results show that nitric oxides (NOdx) and hydrocarbon (HC) emissions are several orders of magnitude lower than at lean operation. Higher loads can be achieved, and brake efficiency is higher than lean operation optimized for low NOdx production. A fast burning (high turbulence) combustion chamber is used to allow high amounts of dilution. (Less)

Number of patients potentially eligible for proton therapy.

Abstract: A group of Swedish radiation oncologists and hospital physicists have estimated the number of patients in Sweden suitable for proton beam therapy in a facility where one of the principal aims is to facilitate randomized and other studies in which the advantage of protons can be shown and the magnitude of the differences compared with optimally administered conventional radiation treatment, also including intensity-modulated radiation therapy (IMRT) and brachytherapy, can be shown. The estimations have been based on current statistics of tumour incidence in Sweden, number of patients potentially eligible for radiation treatment, scientific support from clinical trials and model dose planning studies and knowledge of the dose-response relations of different tumours together with information on normal tissue complication rates. In Sweden, it is assessed that between 2200 and 2500 patients annually are eligible for proton beam therapy, and that for these patients the potential therapeutic benefit is so great as to justify the additional expense of proton therapy. This constitutes between 14-15% of all irradiated patients annually.

Variable Valve Actuation for Timing Control of a Homogeneous Charge Compression Ignition Engine

Abstract: Autoignition of a homogeneous mixture is very sensitiveto operating conditions. Therefore fast combustion phasingcontrol is necessary for reliable operation. There areseveral means to control the combustion phasing of a Homogeneous Charge Compression Ignition (HCCI) engine.This paper presents cycle-to-cycle cylinder individual controlresults from a six-cylinder HCCI engine using a VariableValve Actuation (VVA) system. As feedback signal,the crank angle for 50% burned, based on cylinder pressure,is used. Three control structures are evaluated,Model Predictive Control (MPC), Linear Quadratic Gaussiancontrol (LQG) and PID control. In the control designof the MPC and LQG controller, dynamic models obtainedby system identication were used. Successful experimentswere performed on a port-injected six-cylinderheavy-duty Diesel engine operating in HCCI mode.

Analysis of the Effect of Geometry Generated Turbulence on HCCI Combustion by Multi-Zone Modeling

Abstract: This paper illustrates the applicability of a sequential fluid mechanics, multi-zone chemical kinetics model to analyze HCCI experimental data for two combustion chamber geometries with different levels of turbulence: a low turbulence disc geometry (flat top piston), and a high turbulence square geometry (piston with a square bowl). The model uses a fluid mechanics code to determine temperature histories in the engine as a function of crank angle. These temperature histories are then fed into a chemical kinetic solver, which determines combustion characteristics for a relatively small number of zones (40). The model makes the assumption that there is no direct linking between turbulence and combustion. The results show that the multi-zone model yields good results for both the disc and the square geometries. The model makes good predictions of pressure traces and heat release rates. The experimental results indicate that the high turbulence square geometry has longer burn duration than the low turbulence disc geometry. This difference can be explained by the sequential multi-zone model, which indicates that the cylinder with the square bowl has a thicker boundary layer that results in a broader temperature distribution. This broader temperature distribution tends to lengthen the combustion, as cold mass withinmore » the cylinder takes longer to reach ignition temperature when compressed by the expansion of the first burned gases. The multi-zone model, which makes the basic assumption that HCCI combustion is controlled by chemical kinetics, is therefore capable of explaining the experimental results obtained for different levels of turbulence, without considering a direct interaction between turbulence and combustion. A direct connection between turbulence and HCCI combustion may still exists, but it seems to play a relatively minor role in determining burn duration at the conditions analyzed in this paper.« less

Transient Control of a Multi Cylinder HCCI Engine During a Drive Cycle

Abstract: This study applies a state feedback-based Closed-Loop Combustion Control (CLCC) using Fast Thermal Management (FTM) on a multi-cylinder Variable Compression Ratio (VCR) engine. At speeds above 1500 rpm is the FTM's bandwidth broadened by using the VCR feature of this engine, according to a predefined map, which is a function of load and engine speed. Below 1500 rpm is the PID-based CLCC using VCR applied instead of the FTM while slow cylinder balancing is effectuated by the FTM. Performance of the two CLCC controllers are evaluated during a European EC2000 drive cycle, while HC, CO and CO2 emissions are measured online by a Fast Response Infrared (FRI) emission equipment. A load and speed map calculated for a 1.6L Opel Astra is used to get reference values for the dynamometer speed and the load control. The drive cycle test is initiated from a hot engine and hence no cold start is included. Commercial RON/MON 92/82 gasoline, which corresponds to US regular, is utilized. The Linear Quadratic Gaussian (LQG) state feedback controller handles most tasks well, but has some difficulty with retarded combustion phasings, where the controller is outside of its design range. A mean fuel mileage of 6.8 L/100 km is achieved, which is an improvement of 13% compared to an equivalent SI simulation using steady state data from the same engine. (Less)

An air hybrid for high power absorption and discharge

Abstract: An air hybrid is a vehicle with an ICE modified to also work as an air compressor and air motor. The engine is connected to two air reservoirs, normally the atmosphere and a high pressure tank. The main benefit of such a system is the possibility to make use of the kinetic energy of the vehicle otherwise lost when braking. The main difference between the air hybrid developed in this paper and earlier air hybrid concepts is the introduction of a pressure tank that substitutes the atmosphere as supplier of low air pressure. By this modification, a very high torque can be achieved in compressor mode as well as in air motor mode. A model of an air hybrid with two air tanks was created using the engine simulation code GT-Power. The results from the simulations were combined with a driving cycle to estimate the reduction in fuel consumption. The system was designed to slow down a bus that stops from its maximum speed in urban traffic without using the friction brakes or any other braking system. When this criterion was applied to a 15000 kg bus, the required high pressure tank capacity was 140 litres and the low pressure tank capacity was 600 litres. The low pressure tank can be made very light and is ideally placed on the roof of the vehicle. According to the simulations, 55 percent of the energy absorbed by the engine when braking can be regenerated and returned to the drivetrain. The total reduction in fuel consumption was estimated at 23 percent for urban driving.

Studies of the Combustion Process with Simultaneous Formaldehyde and OH PLIF in a Direct-Injected HCCI Engine

Abstract: This paper presents simultaneous laser based measurements of formaldehyde and OH-radical distributions in a 0.5 liter optical HCCI engine with direct injection. Formaldehyde is formed as an intermediate species when combusting hydrocarbons. The formation occurs through low temperature reactions in an early phase of the combustion process. Later in the process formaldehyde is being consumed. Formaldehyde is, therefore, used as indicator of the first stage of combustion and a marker of zones with low-lemperature reactions. The OH radical is formed as an intermediate during the high temperature reactions, and is used as a marker of zones where the combustion is ongoing. The purpose of the investigation was to study how the combustion process is affected by the change in homogeneity that arises from early and late injection, respectively. The measurement technique used was planar laser-induced fluorescence where formaldehyde was excited at 355 nm and OH at 283 nm. (Less)

Combustion Chamber Wall Temperature Measurement and Modeling During Transient HCCI Operation

Abstract: In this paper the combustion chamber wall temperature was measured by the use of thermographic phosphor. The temperature was monitored over a large time window covering a load transient. Wall temperature measurement provide helpful information in all engines. This temperature is for example needed when calculating heat losses to the walls. Most important is however the effect of the wall temperature on combustion. The walls can not heat up instantaneously and the slowly increasing wall temperature following a load transient will affect the combustion events sucseeding the transient. The HCCI combustion process is, due to its dependence on chemical kinetics more sensitive to wall temperature than Otto or Diesel engines. In depth knowledge about transient wall temperature could increase the understanding of transient HCCI control. A ``black box'' state space model was derived which is useful when predicting transient wall temperature. To produce a model the engine is run with the load described by a Pseudo Random Binary Sequence (PRBS). Standard system identification methodology was then applied to acquire a state space model which calculate the combustion chamber wall temperature given IMEPn. Such a model is useful when controlling HCCI combustion and makes it possible to compensate the impact of wall temperature delay following a load transient. (Less)

Optical Diagnostics of HCCI and UNIBUS Using 2-D PLIF of OH and Formaldehyde

Abstract: Simultaneous OH- and formaldehyde planar-LIF measurements have been performed in an optical engine using two laser sources working on 283 and 355 nm, respectively. The measurements were performed in a light- duty diesel engine, using n-heptane as fuel, converted to single- cylinder operation and modified for optical access. It was also equipped with a direct-injection, common-rail system as well as an EGR system. The engine was operated in both HCCI mode, using a single fuel injection, and UNIBUS (Uniform Bulky Combustion System) mode, using two injections of fuel with one of the injections at 50 CAD before TDC and the other one just before TDC. The OH and formaldehyde LIF images were compared with the heat- release calculated from the pressure-traces. Analyses of the emissions, for example NOx and HC, were also performed for the different operating conditions. (Less)

The potential of proton beam radiation therapy in gastrointestinal cancer

Abstract: A group of Swedish oncologists and hospital physicists have estimated the number of patients in Sweden suitable for proton beam therapy. The estimations have been based on current statistics of tumour incidence, number of patients potentially eligible for radiation treatment, scientific support from clinical trials and model dose planning studies and knowledge of the dose-response relations of different tumours and normal tissues. In gastrointestinal cancers, it is assessed that at least 345 patients, mainly non-resectable rectal cancers, oesophageal and liver cancers, are eligible. Great uncertainties do however exist both in the number of patients with gastrointestinal cancers suitable for radiation therapy, and in the proportion of those where proton beams may give sufficiently better results.

Fuel Effects on Ion Current in an HCCI Engine

Abstract: An interest in measuring ion current in Homogeneous Charge Compression Ignition (HCCI) engines arises when one wants to use a cheaper probe for feedback of the combustion timing than expensive piezo electric pressure transducers. However the location of the ion current probe, in this case a spark plug, is of importance for both signal strength and the crank angle position where the signal is obtained. Different fuels will probably affect the ion current in both signal strength and timing and this is the main interest of this investigation. The measurements were performed on a Scania D12 engine in single cylinder operation and ion current was measured at 7 locations simultaneously. By arranging this setup there was a possibility to investigate if the ion current signals from the different spark plug locations would correlate with the fact that, for this particular engine, the combustion starts at the walls and propagates towards the center of the combustion chamber. The fuels investigated were isooctane, n-heptane, PRF80, gasoline, diesel, ethanol and methanol. A special interest was how the ion current timing was affected by low temperature reactions, which were present with the n-heptane and diesel fuels as well as mixtures of isooctane and n-heptane, i.e., PRF80. The most interesting results were that ion current is both affected by the ion current probe location in the combustion chamber and the fuel used. Fuels with higher octane numbers seem to provoke ion current more easily, thus with LTR fuels as n-heptane and diesel ion current was only achieved at richer mixtures. The cycle-to-cycle variations of ion current increased with leaner mixtures. Ion current was also affected by combustion phasing and engine speed. (Less)

Cycle Resolved Wall Temperature Measurements Using Laser-Induced Phosphorescence in an HCCI Engine

Abstract: Cycle-resolved wall temperature measurements have been performed in a one-cylinder, port-injected optical Scania D12 truck engine run in HCCI mode. Point measurements at various locations were made using Laser-Induced Phosphorescence (LIP). Single point measurements with thermographic phosphors utilize the temperature dependency of the phosphorescence decay time. The phosphorescence peak at 538 nm from the thermographic phosphor La2O2S:Eu was used to determine temperature. A frequency tripled 10 Hz pulsed Nd:YAG laser delivering ultraviolet (UV) radiation at 355 nm was used for excitation of the phosphor. Detection in the spectral region 535 - 545 nm was performed every cycle with a photo multiplier tube connected to a 3 GHz oscilloscope. Measurements were made at four points on the cylinder head surface and two points on the outlet and inlet valves respectively. For each location measurements were made at different loads and at different crank angle degrees (CAD). The aim of the presented work was to study the feasibility of using LIP for single-shot, cycle-resolved wall temperature measurements. (Less)

High-Speed LIF Imaging for Cycle-Resolved Formaldehyde Visualization in HCCI Combustion

Abstract: High-speed laser diagnostics was utilized for single-cycle resolved studies of the formaldehyde distribution in the combustion chamber of an HCCI engine. A multi-YAG laser system consisting of four individual Q-switched, flash lamp-pumped Nd:YAG lasers has previously been developed in order to obtain laser pulses at 355 nm suitable for performing LIF measurements of the formaldehyde molecule. Bursts of up to eight pulses with very short time separation can be produced, allowing capturing of LIF image series with high temporal resolution. The system was used together with a high-speed framing camera employing eight intensified CCD modules, with a frame-rate matching the laser pulse repetition rate. The diagnostic system was used to study the combustion in a truck-size HCCI engine, running at 1200 rpm using n-heptane as fuel. By using laser pulses with time separations as short as 70 μs, cycle-resolved image sequences of the formaldehyde distribution were obtained. Thus, with this technique it is possible to follow the formaldehyde formation and consumption processes within a single cycle. The combustion evolution was studied in terms of the rate and spatial structure of formaldehyde formation and consumption for different engine operating conditions, e.g. different stoichiometries. Also, the impact on the rate of heat-release was investigated.

Simultaneous PLIF Measurements for Visualization of Formaldehyde- and Fuel- Distributions in a DI HCCI Engine

Abstract: Simultaneous laser-induced fluorescence (LIF) imaging of formaldehyde and a fuel-tracer have been performed in a direct-injection HCCI engine. A mix of N-heptane and iso-octane was used as fuel and Toluene as fluorescent tracer. The experimental setup involves two pulsed Nd:YAG lasers and two ICCD cameras. Frequency-quadrupled laser radiation at 266 nm from one of the Nd:YAG lasers was used for excitation of the fuel tracer. The resulting fluorescence was detected with one of the ICCD cameras in the spectral region 270-320 nm. The second laser system provided frequency-tripled radiation at 355 nm for excitation of formaldehyde. Detection in the range 395-500 nm was achieved with the second ICCD. The aim of the presented work is to investigate the applicability of utilizing formaldehyde as a naturally occurring fuel marker. Formaldehyde is formed in the low-temperature reactions (LTR) prior to the main combustion and should thus be present were fuel is located until it is consumed. Measurements were performed when injecting fuel early and late in the compression stroke. Early injection timing results in a homogeneous charge at the time of auto-ignition, while late timing gives a more stratified charge. The crank angle position at which measurements were performed was altered to cover the entire combustion cycle. The measurement images show instantaneous distributions of toluene and formaldehyde respectively. Images from both early and late injection and at all crank angle degrees show good spatial resemblance between toluene signal area and formaldehyde signal area. The work presented in this paper shows that formaldehyde is a feasible alternative to traditional fuel tracers for visualizing fuels featuring low-temperature reactions in HCCI combustion

Quantification of the Formaldehyde Emissions from Different HCCI Engines Running on a Range of Fuels

Abstract: In this paper, the formaldehyde emissions from three different types of homogenous charge compression ignition (HCCI) engines are quantified for a range of fuels by means of Fourier Transform Infra Red (FTIR) spectroscopic analysis. The engines types are differentiated in the way the charge is prepared. The characterized engines are; the conventional port fuel injected one, a type that traps residuals by means of a Negative Valve Overlap (NVO) and finally a Direct Injected (DI) one. Fuels ranging from pure n-heptane to iso-octane via diesel, gasoline, PRF80, methanol and ethanol were characterized. Generally, the amount of formaldehyde found in the exhaust was decreasing with decreasing air/fuel ratio, advanced timing and increasing cycle temperature. It was found that increasing the source of formaldehyde i.e. the ratio of heat released in the cool-flame, brought on higher exhaust contents of formaldehyde. The application of a standard three-way catalyst completely removed formaldehyde from the exhaust stream.

The potential of proton beam radiation therapy in prostate cancer, other urological cancers and gynaecological cancers.

Abstract: A group of Swedish oncologists and hospital physicists have estimated the number of patients in Sweden suitable for proton beam therapy. The estimations have been based on current statistics of tumour incidence, number of patients potentially eligible for radiation treatment, scientific support from clinical trials and model dose planning studies and knowledge of the dose-response relations of different tumours and normal tissues. In prostate cancer it is estimated that annually about 300 patients and in gynaecological cancer about 50 patients, are candidates for proton beam therapy. Owing to major uncertainties, it has not been possible to give an estimate of the number of potential patients with urinary bladder cancer.

Investigation of Boundary Layer Behaviour in HCCI Combustion using Chemiluminescence Imaging

Abstract: Investigation of Boundary Layer Behavior in Hcci Combustion Using Chemiluminescence Imaging

Simultaneous Formaldehyde and Fuel-Tracer LIF Imaging in a High-Speed Diesel Engine With Optically Accessible Realistic Combustion Chamber

Abstract: Simultaneous laser-induced fluorescence (LIF) imaging of formaldehyde and a fuel-tracer have been performed in a high-speed diesel engine. N-heptane and isooctane were used as fuel and toluene was used as a tracer. This arrangement made it possible to make simultaneous measurements of toluene by exciting at 266 nm and detecting at 270-320 nm while exciting formaldehyde at 355 nm and detecting at 400-500 nm.The aim of this study is to investigate how traditional fuel tracer and natural-occurring formaldehyde formed in the cool chemistry are transported in the piston bowl. A range of ignition delays were created by running the engine with different amounts of EGR. During this sweep the area where the low-temperature reactions take place were studied.The measurements were performed in a 0.5-l, single-cylinder optical engine running under conditions simulating a cruise-point, i.e., about 2.2 bar imep. The ignition delay was elongated compared to the normal mapping and the engine-out emissions of soot and NOx were ultra-low.It was found that the spatial location of LTR's does not shift significantly for different EGR levels. The formaldehyde signal overlaps the fuel signal in most cases before the onset of the main heat release.

Influence of homogeneity on HCCI combustion

Abstract: A new laser technique for detecting the air/fuel mixture in the combustion process is presented as a method for improving cycle-by-cycle variations in an HCCI engine.