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Technical Paper
2014-10-13
Hadeel Solaka Aronsson, Ida Truedsson, Martin Tuner, Bengt Johansson, William Cannella
The current research focus on fuel effects on low temperature reactions (LTR) in Homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC). LTR result in a first stage of heat release with decreasing reaction speed at increasing temperature. This makes LTR important for the onset of the main combustion. However, auto-ignition is also affected by other parameters and all fuel does not exhibit LTR. Moreover, the LTR does not only depend on fuel type but also on engine conditions. This research aims to understand the importance of LTR for HCCI and PPC and how fuel composition affects LTR in each type of combustion mode. The HCCI experiment was carried out in co-operative fuel research (CFR) engine, while PPC experiment was carried out in a single cylinder high speed direct injected (HSPDI) diesel engine. A Gaussian profile was used to determine the fraction of LTR for each type of combustion. The fuels used in this study are a blend of ethanol, n-heptane, and isooctane (ERF) and toluene, n-heptane, and isooctane (TRF).
Technical Paper
2014-10-13
Slavey Tanov, Robert Collin, Bengt Johansson, Martin Tuner
Partially Premixed Combustion (PPC) is used to meet the increasing demands of emission legislation and to improve fuel efficiency. PPC with gasoline fuels have the advantage of a longer premixed duration of fuel/air mixture which prevents soot formation at higher loads. The objective of this paper is to investigate the degree of stratification of low load (towards idle) engine conditions for different multiple – injection strategies and negative valve overlap. The question is, how homogenous is the partially premixed combustion for a given setting of negative valve overlap and fuel injection strategy. In this work PRF 69 has been used as PPC fuel. The experimental engine is a light duty diesel engine that has been modified to a single cylinder to provide optical access into the combustion chamber, equipped with a fully variable valve train system. Hot residual gases are trapped by using negative valve overlap. An images of chemiluminescence of the combustion chamber are allowing to follow the combustion process and to analyze the degree of stratification.
Technical Paper
2014-10-13
Martin Tuner, Thomas Johansson, Hans Aulin, Per Tunestal, Bengt Johansson, William Cannella
A 1.9l VGT turbocharged diesel engine was used to investigate partially premixed combustion, PPC, operation using RON 70 gasoline. With the standard hardware an operating range for PPC from idle at 1000 rpm up to a peak load of 10 bar IMEPnet at 3000 rpm could be reached. Compared to conventional diesl combustion, CDC, higher efficiency combined with low NOx and soot operation could be realized with gasoline PPC. Typically, soot levels where three orders of magnitude lower than for CDC. Low pressure EGR routing was beneficial for efficiency and combined with the maximum possible injection pressure of 1500 bar a peak gross indicated efficiency of above 51% was recorded, regardless if a single or double injection strategy was used. The split injection strategy showed in general slightly higher efficiency and did lead to noticeable smoother engine operation with a strong reduction of combustion noise, but was plagued with a major increase of soot emissions. The reason for this increase of soot could possibly be found in the short pulse in-between injections that could lead to increased droplet size.
Technical Paper
2014-10-13
Ida Truedsson, William Cannella, Bengt Johansson, Martin Tuner
This study examines fuel auto-ignitability and shows a method for determining fuel performance for HCCI combustion by doing engine experiments. Previous methods proposed for characterizing HCCI fuel performance were assessed in this study and found not able to predict required compression ratio for HCCI auto-ignition (CRAI) at a set combustion phasing. The previous indices that were studied were the Octane Index (OI), developed by Kalghatgi, and the HCCI Index, developed by Shibata and Urushihara. Fuels with the same OI or HCCI Index were seen to correspond to a wide range of compression ratios in these experiments, so a new way to describe HCCI fuel performance was sought. The Lund-Chevron HCCI Number was developed, using fuel testing in a CFR engine just as for the indices for spark ignition (research octane number and motor octane number, RON and MON) and compression ignition (cetane number, CN). By running the engine in HCCI mode, the required compression ratio for achieving auto-ignition with a combustion phasing of CA50 3° after TDC was determined for various gasoline surrogate fuels prepared from blends of n-heptane, iso-octane, toluene, and ethanol.
Technical Paper
2014-10-13
Ida Truedsson, William Cannella, Bengt Johansson, Martin Tuner
Homogeneous charge compression ignition (HCCI) is a promising concept that can be used to reduce NOx and soot emissions in combustion engines, keeping efficiency as high as for diesel engines. To be able to accurately control the combustion behavior, more information is needed about the auto-ignition of fuels. Many fuels, especially those containing n-paraffins, exhibit pre-reactions before the main heat release event, originating from reactions that are terminated when the temperature in the cylinder reaches a certain temperature level. These pre-reactions are called low temperature heat release (LTHR), and are known to be affected by engine speed. This paper goes through engine speed effects on auto-ignition temperatures and LTHR for primary reference fuels. Earlier studies show effects on both quantity and timing of the low temperature heat release when engine speed is varied. In this study, these effects are further explored by looking at the auto-ignition temperatures and the pressure and temperature evolution in the cylinder.
Technical Paper
2014-10-13
Kenan Muric, Ola Stenlaas, Per Tunestal, Bengt Johansson
n the last couple of decades, countries have enacted new laws concerning environmental pollution caused by heavy-duty commercial and passenger vehicles. This is done mainly in an effort to reduce smog and health impacts caused by the different pollutions. One of the legislated pollutions, among a wide range of regulated pollutions, is nitrogen oxides (commonly abbreviated as NOx). The SCR (Selective Catalytic Reduction) was introduced in the automotive industry to reduce NOx emissions leaving the vehicle. The basic idea is to inject a urea solution (AdBlue™) in the exhaust gas before the gas enters the catalyst. The optimal working temperature for the catalyst is somewhere in the range of 300 to 400 Celsius. For the reactions to occur without a catalyst, the gas temperature has to be at least 800 oC. These temperatures only occur in the engine cylinder itself, during and after the combustion. In this paper a study is presented where a second injector is installed in a Scania D13 cylinder head for urea injection purposes.
Technical Paper
2014-04-01
Rikard Wellander, Joakim Rosell, Mattias Richter, Marcus Alden, Oivind Andersson, Bengt Johansson, Jeudi Duong, Jari Hyvonen
In this work the pre- to main chamber ignition process is studied in a Wärtsilä 34SG spark-ignited lean burn four-stroke large bore optical engine (bore 340 mm) operating on natural gas. Unburnt and burnt gas regions in planar cross-sections of the combustion chamber are identified by means of planar laser induced fluorescence (PLIF) from acetone seeded to the fuel. The emerging jets from the pre-chamber, the ignition process and early flame propagation are studied. Measurements reveal the presence of a significant temporal delay between the occurrence of a pressure difference across the pre-chamber holes and the appearance of hot burnt/burning gases at the nozzle exit. Variations in the delay affect the combustion timing and duration. The combustion rate in the pre-chamber does not influence the jet propagation speed, although it still has an effect on the overall combustion duration. PLIF images also show that there is mainly lean unburnt gas, originating from the main-chamber, that exit the pre-chamber in the initial phase of ignition, indicating incomplete mixing of the gases in the pre-chamber prior ignition.
Technical Paper
2014-04-01
Ashish Shah, Per Tunestal, Bengt Johansson
Abstract This article deals with application of a pre-chamber type ignition device in a heavy duty engine operated with natural gas. A particular pre-chamber ignition strategy called Avalanche Activated Combustion (originally ‘Lavinia Aktyvatsia Gorenia’ in Russian), commonly referred to as LAG-ignition process, has been studied by performing a parametric study of various pre- and main chamber mixture strength combinations. This strategy was first proposed in 1966 and has been mostly applied in light duty automotive engines. A majority of published data are results from developmental studies but the fundamental mechanism of the LAG-ignition process is unclear to date. To the best of authors' knowledge, the study presented in this article is the first generalized study to gain deeper understanding of the LAG-ignition process in heavy duty engines operating with natural gas as fuel for both chambers. The experiments are performed on a single cylinder 2.1 L engine fitted with a custom made pre-chamber capable of spark ignition, fuel injection and pressure measurement.
Technical Paper
2014-04-01
Hadeel Solaka Aronsson, Martin Tuner, Bengt Johansson
Abstract Gasoline fuels are complex mixtures which consist of more than 200 different hydrocarbon species. In order to decrease the chemical and physical complexity, oxygenated surrogate components were used to enhance the fundamental understanding of partially premixed combustion (PPC). The ignition quality of a fuel is measured by octane number. There are two methods to measure the octane number: research octane number (RON) and motor octane number (MON). In this paper, RON and MON were measured for a matrix of n-heptane, isooctane, toluene, and ethanol (TERF) blends spanning a wide range of octane number between 60.6 and 97. First, regression models were created to derive RON and MON for TERF blends. The models were validated using the standard octane test for 17 TERF blends. Second, three different TERF blends with an ignition delay (ID) of 8 degrees for a specific operating condition were determined using a regression model. This was done to examine the model accuracy for ID and study fuel composition effect on combustion events and emissions.
Technical Paper
2013-10-14
Hadeel Solaka, Martin Tuner, Bengt Johansson, William Cannella
Partially premixed combustion (PPC) is intended to improve fuel efficiency and minimize the engine-out emissions. PPC is known to have the potential to reduce emissions of nitrogen oxides (NOx) and soot, but often at the expense of increased emissions of unburned hydrocarbons (HC) and carbon monoxide (CO). PPC has demonstrated remarkable fuel flexibility and can be operated with a large variety of liquid fuels, ranging from low-octane, high-cetane diesel fuels to high-octane gasolines and alcohols. Several research groups have demonstrated that naphtha fuels provide a beneficial compromise between functional load range and low emissions. To increase the understanding of the influence of individual fuel components typically found in commercial fuels, such as alkenes, aromatics and alcohols, a systematic experimental study of 15 surrogate fuel mixtures of n-heptane, isooctane, toluene and ethanol was performed in a light-duty PPC engine using a design of experiment methodology. The impacts of oxygen concentration, injection pressure, combustion phasing and premixed fraction were investigated for all fuel blends.
Technical Paper
2013-10-14
Kihyun Kim, Choongsik Bae, Bengt Johansson
Spray and combustion of gasoline and diesel were visualized under different ambient conditions in terms of pressure, temperature and density in a constant volume chamber. Three different ambient conditions were selected to simulate the three combustion regimes of homogeneous charge compression ignition, premixed charge compression ignition and conventional combustion. Ambient density was varied from 3.74 to 23.39 kg/m3. Ambient temperature at the spray injection were controlled to the range from 474 to 925 K. Intake oxygen concentration was also modulated from 15 % to 21 % in order to investigate the effects of intake oxygen concentrations on combustion characteristics. The injection pressure of gasoline and diesel were modulated from 50 to 150 MPa to analyze the effect of injection pressure on the spray development and combustion characteristics. Liquid penetration length and vapor penetration length were measured based on the methods of Mie-scattering and Schileren, respectively. Direct combustion visualization was also carried out to figure out the lift-off length and flame structure.
Technical Paper
2013-10-14
Prakash Narayanan Arunachalam, Martin Tuner, Per Tunestal, Bengt Johansson, Marcus Thern
In the quest for efficiency improvement in heavy duty truck engines, waste heat recovery could play a valuable role. The evaporative cycle is a waste heat recovery technology aimed at improving efficiency and decreasing emissions. A humid air motor (HAM) uses the waste heat from the exhaust of the engine to humidify the inlet air; this humid air, with higher specific heat, reduces NOx emission to a greater extent [1] [2]. Despite this benefit of emission reduction, the increase or decrease in efficiency of the humid air motor compared to the conventional engine is not discussed in the literature [3] [4] [5]. In this paper, an attempt is made to study the efficiency of the HAM using system model simulations of a 13-liter heavy duty Volvo engine with a humidifier. The commercial software GT-SUITE is used to build the system model and to perform the simulations. The efficiency improvement of the HAM comes from the expansion of the vapor mass flow produced as a result of humidification. An effort is also made to understand the relationship between the humidified engine and its efficiency.
Technical Paper
2013-10-14
Ida Truedsson, Martin Tuner, Bengt Johansson, William Cannella
HCCI combustion can be enabled by many types of liquid and gaseous fuels. When considering what fuels will be most suitable, the emissions also have to be taken into account. This study focuses on the emissions formation originating from different fuel components. A systematic study of over 40 different gasoline surrogate fuels was made. All fuels were studied in a CFR engine running in HCCI operation. Many of the fuels were blended to achieve similar RON's and MON's as gasoline fuels, and the components (n-heptane, iso-octane, toluene, and ethanol) were chosen to represent the most important in gasoline; nparaffins, iso-paraffins, aromatics and oxygenates. The inlet air temperature was varied from 50°C to 150°C to study the effects on the emissions. The compression ratio was adjusted for each operating point to achieve combustion 3 degrees after TDC. The engine was run at an engine speed of 600 rpm, with ambient intake air pressure and with an equivalence ratio of 0.33. NOx emissions were low for all operating points, and ethanol and toluene addition was found to decrease NOx emissions for higher octane fuels.
Technical Paper
2013-10-14
Marcus Lundgren, Martin Tuner, Bengt Johansson, Simon Bjerkborn, Karin Frojd, Arne Andersson, Fabian Mauss, Bincheng Jiang
The relatively new combustion concept known as partially premixed combustion (PPC) has high efficiency and low emissions. However, there are still challenges when it comes to fully understanding and implementing PPC. Thus a predictive combustion tool was used to gain further insight into the combustion process in late cycle mixing. The modeling tool is a stochastic reactor model (SRM) based on probability density functions (PDF). The model requires less computational time than a similar study using computational fluid dynamics (CFD). A novel approach with a two-zone SRM was used to capture the behavior of the partially premixed or stratified zones prior to ignition. This study focuses on PPC mixing conditions and the use of an efficient analysis approach. It was done in three steps: a validation of the two-zone SRM against CFD and experimental data, a parametric study using a design of experiment (DOE) approach to late cycle mixing conditions, and analyses of fuel mass distribution with time-resolved probability density functions (TPDF).
Technical Paper
2013-10-14
Kenan Muric, Ola Stenlaas, Per Tunestal, Bengt Johansson
The emission control in heavy-duty vehicles today is based on predefined injection strategies and after-treatment systems such as SCR (selective catalytic reduction) and DPF (diesel particulate filter). State-of-the-art engine control is presently based on cycle-to-cycle resolution. The introduction of the crank angle resolved pressure measurement, from a piezo-based pressure sensor, enables the possibility to control the fuel injection based on combustion feedback while the combustion is occurring. In this paper a study is presented on the possibility to control NOx (nitrogen oxides) formation with a crank angle resolved NOx estimator as feedback. The estimator and the injection control are implemented on an FPGA (Field-Programmable Gate Array) to manage the inherent time constraints. The FPGA is integrated with the rest of the engine control system for injection control and measurement. Studies of injection strategies show that one of the feasible approaches, using a solenoid injector to control NOx, is a split-main injection based strategy.
Technical Paper
2013-10-14
Jessica Dahlstrom, Alessandro Schönborn, Per Tunestal, Bengt Johansson
Using diluted methane/air mixtures in internal combustion engines has a potential of reducing emissions and increasing efficiency. However, the ignition systems used today show difficulties igniting lean mixtures. For this purpose a new high frequency (HF) ignition system using pulse generators and a resonance circuit to achieve a controlled number of sparks during a controlled period of time has been developed. A first prototype of this high frequency system has been tested in a flow-reactor and compared to a conventional ignition system. Results show that the high frequency system improves the flame development under lean conditions compared to the conventional system. Higher frequencies have higher capability of igniting lean mixtures than lower frequencies. Lower spark frequencies were found to travel faster across the electrodes than high frequencies and also compared to the conventional system. High pressure and high flow rates affected the lean limit of all ignition strategies, but especially high spark frequencies had difficulties igniting the charge under high pressures, due to the resonant frequency changing with pressure.
Technical Paper
2013-10-14
Martin Tuner, Bengt Johansson, Philip Keller, Michael Becker
Partially Premixed Combustion (PPC) has demonstrated substantially higher efficiency compared to conventional diesel combustion (CDC) and gasoline engines (SI). By combining experiments and modeling the presented work investigates the underlying reasons for the improved efficiency, and quantifies the loss terms. The results indicate that it is possible to operate a HD-PPC engine with a production two-stage boost system over the European Stationary Cycle while likely meeting Euro VI and US10 emissions with a peak brake efficiency above 48%. A majority of the ESC can be operated with brake efficiency above 44%. The loss analysis reveals that low in-cylinder heat transfer losses are the most important reason for the high efficiencies of PPC. In-cylinder heat losses are basically halved in PPC compared to CDC, as a consequence of substantially reduced combustion temperature gradients, especially close to the combustion chamber walls. Pumping losses are on the other hand three times higher than for CDC due to the increased mass flow rate over the valves from the charge dilution and the high amounts of EGR.
Technical Paper
2013-10-14
Mengqin Shen, Martin Tuner, Bengt Johansson, William Cannella
Partially Premixed Combustion (PPC) has the potential of simultaneously providing high engine efficiency and low emissions. Previous research has shown that with proper combination of Exhaust-Gas Recirculation (EGR) and Air-Fuel equivalence ratio, it is possible to reduce engine-out emissions while still keeping the engine efficiency high. In this paper, the effect of changes in intake pressure (boost) and EGR fraction on PPC engine performance (e.g. ignition delay, burn duration, maximum pressure rise rate) and emissions (carbon monoxide (CO), unburned hydrocarbon (UHC), soot and NOX) was investigated in a single-cylinder, heavy-duty diesel engine. Swedish diesel fuel (MK1), RON 69 gasoline fuel and 99.5 vol% ethanol were tested. Fixed fueling rate and single injection strategy were employed. For diesel and gasoline PPC, in those conditions with a predominantly mixing-controlled combustion process, increasing EGR or reducing intake boost could increase ignition delay and shorten burn duration.
Technical Paper
2013-09-08
Jos Reijnders, Michael Boot, Philip de Goey, Bengt Johansson
Styrene, or ethylbenzene, is mainly used as a monomer for the production of polymers, most notably Styrofoam. In the synthetis of styrene, the feedstock of benzene and ethylene is converted into aromatic oxygenates such as benzaldehyde, 2-phenyl ethanol and acetophenone. Benzaldehyde and phenyl ethanol are low value side streams, while acetophenone is a high value intermediate product. The side streams are now principally rejected from the process and burnt for process heat. Previous in-house research has shown that such aromatic oxygenates are suitable as diesel fuel additives and can in some cases improve the soot-NOx trade-off. In this study acetophenone, benzaldehyde and 2-phenyl ethanol are each added to commercial EN590 diesel at a ratio of 1:9, with the goal to ascertain whether or not the lower value benzaldehyde and 2-phenyl ethanol can perform on par with the higher value acetophenone. These compounds are now used in pure form. In future work, real streams, which are rich of these compounds, but contain various other chemicals as well, will be used.
Technical Paper
2013-04-08
Mehrzad Kaiadi, Bengt Johansson, Marcus Lundgren, John A. Gaynor
Partially Premixed Combustion (PPC) is a combustion concept which aims to provide combustion with low smoke and NOx with high efficiency. Extending the ignition delay to enhance the premixing, avoiding spray-driven combustion and controlling the combustion temperature to optimum levels through use of suitable lambda and EGR levels, have been recognized as key factors to achieve such combustion. Fuels with high ignitability resistance have been proven to be a good mean to extend the ignition delay. In this work pure ethanol has been used as a PPC fuel. The objective of this research was to investigate a suitable injection strategy for PPC combustion fueled with ethanol. Extensive experimental investigations were performed on a single-cylinder heavy-duty engine. The number of injections for each cycle, timing of the injections and the ratio between different injection pulses was varied one at a time and the combustion behavior was investigated at medium and low loads. The engine performance was evaluated in terms of controllability, stability, combustion noise, emissions and different efficiencies.
Technical Paper
2013-04-08
Mehrzad Kaiadi, Bengt Johansson, Marcus Lundgren, John A. Gaynor
Partially Premixed Combustion (PPC) is a combustion concept which aims to provide combustion with low smoke and NOx with high thermal efficiency. Extending the ignition delay to enhance the premixing, avoiding spray-driven combustion and controlling the combustion temperature at an optimum level through use of suitable lambda and EGR levels have been recognized as key factors to achieve such a combustion. Fuels with high ignitability resistance have been proven to be a useful to extend the ignition delay. In this work pure ethanol has been used as a PPC fuel. The objective of this research was initially to investigate the required operating conditions for PPC with ethanol. Additionally, a sensitivity analysis was performed to understand how the required parameters for ethanol PPC such as lambda, EGR rate, injection pressure and inlet temperature influence the combustion in terms of controllability, stability, emissions (i.e. HC, CO, NOx and Soot) and combustion and thermodynamic efficiency.
Technical Paper
2013-04-08
Mengqin Shen, Martin Tuner, Bengt Johansson
Partially Premixed Combustion, PPC, with 50% Exhaust Gas Recirculation (EGR) at lean combustion conditions λ =1.5, has shown good efficiency and low emissions in a heavy-duty single-cylinder engine. To meet emission requirements in all loads and transient operation, aftertreatment devices are likely needed. Reducing λ to unity, when a three-way catalyst can be applied, extremely low emissions possibility exists for stoichiometric PPC. In this study, the possibility to operate clean PPC from lean condition to stoichiometric equivalence ratio with reasonable efficiency and non-excessive soot emission was investigated. Two EGR rates, 48% and 38% with two fuel rates were determined for 99.5 vol% ethanol in comparison with one gasoline fuel and Swedish diesel fuel (MK1). Engine was operated at 1250 rpm and 1600 bar injection pressure with single injection. Results revealed that efficiency was reduced and soot emission increased from lean PPC to stoichiometric PPC operation. Significant increase in soot emission and pronounced efficiency reduction makes stoichiometric diesel PPC impossible.
Technical Paper
2013-04-08
Hadeel Solaka, Martin Tuner, Bengt Johansson
Fuel effects on ignition delay and low temperature reactions (LTR) during partially premixed combustion (PPC) were analyzed using Design of Experiments (DoE). The test matrix included seventeen mixtures of n-heptane, isooctane, toluene and ethanol covering a broad range of ignition quality and fuel chemistry. Experiments were performed on a light-duty diesel engine at 8 bar IMEP g , 1500 rpm with a variation in combustion phasing, inlet oxygen concentration and injection pressure. A single injection strategy was used and the start of injection and injection duration were adjusted to achieve the desired load and combustion phasing. The experimental data show that fuels with higher Research Octane Number (RON) values generally produced longer ignition delays. In addition, the alcohol content had significantly stronger effect on ignition delay than the aromatic content. Fuels with more ethanol gave longer ignition delays and a combination of high level of ethanol and toluene produced the longest ignition delay.
Technical Paper
2013-04-08
Patrick Borgqvist, Per Tunestal, Bengt Johansson
Gasoline partially premixed combustion (PPC) has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions. The problem is the ignitability at low load and idle operating conditions. In a previous study it was shown that it is possible to use NVO to improve combustion stability and combustion efficiency at operating conditions where available boosted air is assumed to be limited. NVO has the disadvantage of low net indicated efficiency due to heat losses from recompressions of the hot residual gases. An alternative to NVO is the rebreathing valve strategy where the exhaust valves are reopened during the intake stroke. The net indicated efficiency is expected to be higher with the rebreathing strategy but the question is if similar improvements in combustion stability can be achieved with rebreathing as with NVO. The results show that the rebreathing valve strategy has similar improvements on combustion stability as NVO when the same fuel injection strategy is used.
Technical Paper
2013-04-08
Guillaume Lequien, Edouard Berrocal, Yann Gallo, Augusto Themudo e Mello, Oivind Andersson, Bengt Johansson
The liquid phase penetration of diesel sprays under reacting conditions is measured in an optical heavy-duty Direct Injection (DI) diesel engine. Hot gas reservoirs along the diffusion flames have previously been shown to affect the liftoff length on multi hole nozzles. The aim of this study is to see if they also affect the liquid length. The inter-jet spacing is varied together with the Top Dead Center density and the inlet temperature. To avoid unwanted interferences from the natural flame luminosity the illumination wavelength is blue shifted from the black body radiation spectrum and set to 448 nm. Filtered Mie scattered light from the fuel droplets is recorded with a high speed camera. The liquid fuel penetration is evaluated from the start of injection to the quasi steady phase of the jets. Knowledge of jet-jet interaction effects is of interest for transferring fundamental understanding from combustion vessels to practical engine applications. It is found that the hot gas reservoirs do not significantly affect the liquid length.
Technical Paper
2013-04-08
Jessica Dahlstrom, Per Tunestal, Bengt Johansson
Running an internal combustion engine with diluted methane/air mixtures has a potential of reducing emissions and increasing efficiency. However, diluted mixtures need high ignition energy in a sufficiently large volume, which is difficult to accomplish. Increasing the spark duration has shown to be a promising way of delivering more energy into the diluted charge, but this requires a more sophisticated ignition system. This work focuses on evaluating the effects regarding enhancing early flame development, reducing cyclic variations and extending the lean limit using a new capacitive ignition system as compared to a conventional inductive ignition system. The new system offers the opportunity to customise the spark by altering the electric pulse train characteristics choosing the number of pulses, the length of the individual pulses as well as the time delay between them. Several different spark configurations were evaluated for the new capacitive system, including varying spark duration between approximately 0.5-1.2 ms and maximum current levels of 0.2-0.4 A.
Technical Paper
2013-04-08
Ida Truedsson, Martin Tuner, Bengt Johansson, William Cannella
An index to relate fuel properties to HCCI auto-ignition would be valuable to predict the performance of fuels in HCCI engines from their properties and composition. The indices for SI engines, the Research Octane Number (RON) and Motor Octane Number (MON) are known to be insufficient to explain the behavior of oxygenated fuels in an HCCI engine. One way to characterize a fuel is to use the Auto-Ignition Temperature (AIT). The AIT can be extracted from the pressure trace. Another potentially interesting parameter is the amount of Low Temperature Heat Release (LTHR) that is closely connected to the ignition properties of the fuel. A systematic study of fuels consisting of gasoline surrogate components of n-heptane, iso-octane, toluene, and ethanol was made. 21 fuels were prepared with RON values ranging from 67 to 97. Five different inlet air temperatures ranging from 50°C to 150°C were used to achieve different cylinder pressures and the compression ratio was changed accordingly to keep a constant combustion phasing, CA50, of 3 ± 1° after TDC.
Technical Paper
2012-09-24
Ashish Shah, Per Tunestal, Bengt Johansson
This article deals with application of turbulent jet ignition technique to heavy duty multi-cylinder natural gas engine for mobile application. Pre-chamber spark plugs are identified as a promising means of achieving turbulent jet ignition as they require minimal engine modification with respect to component packaging in cylinder head and the ignition system. Detailed experiments were performed with a 6 cylinder 9.4 liter turbo-charged engine equipped with multi-point gas injection system to compare performance and emissions characteristics of operation with pre-chamber and conventional spark plug. The results indicate that ignition capability is significantly enhanced as flame development angle and combustion duration are reduced by upto 30 % compared to those with conventional spark plugs at certain operating points. Maximum possible dilution (limited by combustion stability index, Coefficient of Variation (COV) of Gross Indicated Mean Effective Pressure (IMEPg)) with excess air and EGR were investigated experimentally at engine speed of 1500 rpm and 5, 12 and 18 bar IMEPg operating load and results indicate that the lean limit is extended by 0.8-1 Lambda unit and 5-8% EGR rate units.
Technical Paper
2012-09-10
Ashish Shah, Per Tunestal, Bengt Johansson
This article deals with study of ionization current sensing technique's signal characteristics while operating with pre-chamber spark plug to achieve plasma jet ignition in a 6 cylinder 9 liter turbo-charged natural gas engine under EGR and excess air dilution. Unlike the signal with conventional spark plug which can be divided into distinct chemical and thermal ionization peaks, the signal with pre-chamber spark plug shows a much larger first peak and a negligible second peak thereafter. Many studies in past have found the time of second peak coinciding with the time of maximum cylinder pressure and this correlation has been used as an input to combustion control systems but the absence of second peak makes application of this concept difficult with pre-chamber spark plug. However, it has been observed that the first peak is very strong and does not deteriorate much even under lean operation and hence ion current signal integral can be used to calculate real time combustion stability parameters for combustion control systems.
Technical Paper
2012-09-10
Patrick Borgqvist, Martin Tuner, Augusto Mello, Per Tunestal, Bengt Johansson
Partially premixed combustion has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions, even at higher loads. The problem is the ignitability at low load and idle operating conditions. The objective is to investigate the usefulness of negative valve overlap on a light duty diesel engine running with gasoline partially premixed combustion at low load operating conditions. The idea is to use negative valve overlap to trap hot residual gases to elevate the global in-cylinder temperature to promote auto-ignition of the high octane number fuel. This is of practical interest at low engine speed and load operating conditions because it can be assumed that the available boost is limited. The problem with NVO at low load operating conditions is that the exhaust gas temperature is low. While an increase of NVO potentially increases the in-cylinder temperature at intake valve closing, increasing NVO also increases the EGR fraction which lowers the global in-cylinder temperature.
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