In-cylinder Surface Thermometry using Laser Induced Phosphorescence

Surface temperature in internal combustion engines is of high interest when studying heat losses. Two approaches for retrieving the surface temperatures are thermocouples and Laser Induced Phosphorescence, LIP. This study aims to analyze LIP as a technique for measuring surface temperature in internal combustion engines. The motivation for this study is the need for accurate surface temperatures which can be used by predictive models and increase knowledge about heat transfer. In this work LIP measurements have been carried out in two optical engines. In the first engine a thermographic phosphor was applied on top of a metal piston. The second engine was fitted with a quartz liner which was coated with phosphor material. Several coating thicknesses have been tested and the LIP temperature was extracted from both opposing sides of the phosphor. Both engines were run in HCCI mode with reference fuels and electrically heated air. In a previous publication, the authors showed that a layer of phosphor can show different temperatures i.e. a higher temperature on the side facing the cylinder gas than on the side facing the wall. In this study it is shown which thickness is needed to accurately present the temperature for typical engine combustion. With an increasing thickness of the phosphor material, the surface gets gradually insulated and the phosphor temperature reading becomes inaccurate. LIP measurements from a quartz ring and a metal piston have been compared and the temperature increase during combustion is similar although the heat conductivity of quartz is 40-200 times smaller than the metal piston. Measurements with thermocouples often show a lower temperature increase than what is seen in the LIP results. The difference in heat conductivity between the phosphor coating and the underlying surface is of importance for understanding what temperature is actually measured

Stochastic Reactor Models for Engine Simulations

The aim of the thesis work is the further development of practical engine simulation tools based on Stochastic Reactor Models, SRMs. Novel and efficient implementations were made of a variety of SRMs adapted to different engine types. The models in question are the HCCI-SRM, the TwoZone SI-SRM and the DI-SRM. The specific models developed were incorporated into two different interfaces: DARS-ESSA, which is a stand-alone tool, and DARS-ESM through which all the models can be operated in a simple and effective manner with use of several commercial 1-D engine simulation tools. The tools and couplings to commercial 1-D codes were successfully developed and employed to simulate such complex combustion processes as of HCCI engines with NVO combustion. SRMs are able to model cyclic variations, but these may be overpredicted if discretization is too coarse. It was found that for studies of cyclic variations in HCCI engines, by using the HCCI-SRM, discretization needs to have a level of resolution of 500 particles and of 0.5 CAD time steps, to provide the correct range of the cyclic variations. To get correct predictions of average values, of for example the pressure, temperature and species mass fractions, as few as 10 cycles are usually required, even when employing as coarse discretization of 100 particles and time steps of 0.5 CAD. Investigations to study the effects of turbulence and heat transfer in HCCI combustion were performed. In the case of high levels of turbulence and evenly distributed heat transfer, the in-cylinder conditions become homogeneous more quickly. The results indicate that in HCCI engines, inhomogeneties tend to promote earlier ignition and lower pressure rates as well as more stable operating conditions with lesser cyclic variations. Turbulence and the heat transfer distribution had little impact on the duration of combustion or on the amount of HC and NO at EVO. The calculated concentrations of hydroxyl radicals and formaldehyde were compared with LIF-measurements made in an optically accessed iso-octane / n-heptane fuelled HCCI engine. The averaged and distributed concentrations of CH2O and OH could be predicted with quite high accuracy by the SRM. This clearly proves the validity of the stochastic reactor model. The formation of exothermic centers was modeled with the SRM to investigate their impact on HCCI combustion. By varying the exhaust valve temperature, and thus assigning more realistic wall temperatures, the formation of exothermic centers and the ignition timing was shifted in time. It was shown that promoting exothermic centers provide more inhomogeneous conditions before ignition, and lead to earlier ignition. This in turn leads to more homogeneous conditions after combustion, counteracting emissions of hydrocarbons and CO which are a problem in HCCI engines. Studies involving the use of a novel approach with adaptive chemistry, POSM, were performed. Incorporated into the Two-Zone SI-SRM code, calculations showed almost no accuracy to be lost, while there was a decrease in calculation time by a factor of 3. For a further gain in calculation speed of a factor of 12, clear losses in accuracy were experienced, although the global conditions were well captured. Simulations of diesel engine combustion, DICI, using the newly developed DI-SRM coupled with a 1-D full engine simulation tool were found to agree well with the results of experiments that were conducted. Parametric studies were performed to indicate the sensitivity of the modeling parameters. The DI-SRM behaved as predicted, and even with use of coarse discretization the results were comparable to those of the experiments

The effect of 2-ethyl-hexyl nitrate on HCCI combustion properties to compensate ethanol addition to gasoline

Stable HCCI combustion requires a proper level of fuel reactivity. This study shows that adding ethanol as a renewable fraction to low octane gasoline decreases the reactivity of the gasoline, while adding 2-ethyl hexyl nitrate (2-EHN) can enhance the reactivity of the blend and counter the effect of ethanol.The experimental apparatus consisted of a modified CFR engine for HCCI combustion equipped with two port fuel injectors and an intake air heater. Gasoline blended with ethanol (10% v/v) was used as the base fuel. Different percentages of 2-EHN (0.25%, 0.50%, 1%, and 2.5%) were added to the base fuel as an ignition improver. The blends were tested at operating points defined for HCCI number at two different engine speeds (600 and 900 rpm) and three different intake temperatures (50, 100, and 150 °C) to investigate the effect of 2-EHN on the auto-ignition behavior of the fuel.Combustion, emissions, and performance parameters of HCCI combustion of the blends were measured. The presence of 2-EHN in the blends improved the auto-ignitability of the blends in a nonlinear manner. It was also found that 0.25% of 2-EHN can compensate for the effect of ethanol on the required compression ratio and remove the quenching effect of ethanol on low temperature heat release. The results show that for the same fuel, a higher compression ratio is needed to maintain the combustion phasing constant at a higher engine speed

Evaluation of engine efficiency, emissions and load range of a PPC concept engine, with higher octane and alkylate gasoline

Gasoline Compression Ignition research has shown that it can provide diesel like engine efficiency while maintaining gasoline like exhaust emissions. While research has shown that lower octane fuels might be good for that, they are also not available now. A good compromise for that would be the use of higher octane gasoline which is available in most places. For this study, experiments were performed under Partially Premixed Combustion (PPC) conditions with RON 90 gasoline, in a 2 L multi-cylinder diesel engine which complies with Euro 6 emissions standards. The aim is to evaluate the efficiency, the emissions and the achievable load in terms of minimum and maximum at three different speeds, 1200, 1800 2400 rpm and with two different RON 90 gasolines and the standard diesel engine hardware. The two fuels were a regular pump gasoline and an alkylate gasoline, which was chosen to represent a pathway to a renewable fuel. Results show that the minimum load is around 5 bar IMEPg, limited by high COV (coefficient of variation) values and high air intake temperature, while the maximum load reaches 18 bar IMEPg, limited by lambda value, pressure and mechanical limitations. While efficiency is similar between the two fuels with a brake value of around 40%, at higher loads the alkylate fuel produces higher amounts of soot while the regular gasoline has higher carbon monoxide at low loads. Finally, an energy balance comparison between the two gasolines and diesel is made, showing improved efficiency and soot emissions under PPC

Phase optimized skeletal mechanisms for engine simulations

Adaptive chemistry is based on the principle that instead of having one comprehensive model describing the entire range of chemical source term space (typically parameters related to temperature, pressure and species concentrations), a set of computationally simpler models are used, each describing a local region (in multidimensional space) or phases (in zero-dimensional space). In this work, an adaptive chemistry method based on phase optimized skeletal mechanisms (POSM) is applied to a 96 species n-heptane-isooctane mechanism within a two-zone zero-dimensional stochastic reactor model (SRM) for an spark-ignition (SI) Engine. Two models differing only in the extent of reduction in the phase mechanism, gave speed-up factors of 2.7 and 10. The novelty and emphasis of this study is the use of machine learning techniques to decide where the phases are and to produce a usable phase recognition. The combustion process is automatically divided up into an 'optimal' set of phases through machine learning clustering based on fuzzy logic predicates involving a necessity parameter (a measure giving an indication whether a species should be included in the mechanism or not). The mechanism of each phase is reduced from the full mechanism based on this necessity parameter with respect to the conditions of that phase. The algorithm to decide which phase the process is in is automatically determined by another machine learning method that produces decision trees. The decision tree is made up of asking whether the mass fraction values were above or below given values. Two POSM studies were done, a conservative POSM where the species in each phase are eliminated based on a necessity parameter threshold (speed-up 2.7) and a further reduced POSM where each phase was further reduced by hand (speed-up 10). The automated techniques of determining the phases and for creating the decision tree are very general and are not limited to the parameter choices of this paper. There is also no fundamental limit as to the size of the original detailed mechanism. The interfacing to include POSM in an application does not differ significantly from using the original detailed mechanism

Investigation of environmental, operational and economic performance of methanol partially premixed combustion at slow speed operation of a marine engine

This study aims to investigate the environmental, operational and economic performance of the methanol partially premixed combustion concept at slow speed operation of a ship to find a solution for the shipping emission effect on the coastal settlements while do not increase the risk and expense of the engine operation on the ships. The experimental study was done with partially premixed combustion, one of the advanced combustion concepts, on a Scania D13 heavy-duty diesel engine for its promising results of high engine efficiency and low engine emissions. In addition to the experimental study with methanol fuel, the performance of the methanol was compared with marine gas oil, which was mostly used at the slow speed operation of the ships. Empirical equations and coefficients in the literature were used to calculate specific fuel consumption, efficiency, and emissions of the marine gas oiled operation of the engine. The results showed that the combustion efficiency varied from 0.94 to 0.99 and the gross indicated efficiency varied from 0.42 to 0.46 from 10% to 25% engine loads, respectively, while the gross indicated efficiency of the marine gas oil-fuelled engine was 0.32 as a maximum value. The methanol showed good environmental performance with lower CO2 emissions than the marine gas oil, lower NOX emissions than the NOX Tier III levels, varied between 0.3 g/kWh and 1.4 g/kWh, zero SOX emissions and zero PM emissions. The economic investigation showed that the methanol cost at the low price scenario was 0.147 $/kWh, 0.138$/kWh and 0.135 $/kWh at 10%, 15% and 25%, respectively, which were lower than the high price scenario and low price scenario of the marine gas oil; and the methanol high price scenario was still competitive with the marine gas oil scenarios

Förgasning-Gasmotor för småskalig kraft-värme

In a joint project, Linnaeus University in Växjö (LNU) and the Faculty of Engineering at Lund University (LTH) were commissioned by the Swedish Energy Agency to make an inventory of the techniques and systems for small scale gasifier-gas engine combined heat and power (CHP) production and to evaluate the technology. Small scale is defined here as plants up to 10 MWth, and the fuel used in the gasifier is some kind of biofuel, usually woody biofuel in the form of chips, pellets, or sawdust. The study is presented in this report. The report has been compiled by searching the literature, participating in seminars, visiting plants, interviewing contact people, and following up contacts by e-mail and phone. The first, descriptive part of the report, examines the state-of-the-art technology for gasification, gas cleaning, and gas engines. The second part presents case studies of the selected plants: Meva Innovation’s VIPP-VORTEX CHP plant DTU’s VIKING CHP plant Güssing bio-power station Harboøre CHP plant Skive CHP plant The case studies examine the features of the plants and the included unit operations, the kinds of fuels used and the net electricity and overall efficiencies obtained. The investment and operating costs are presented when available as are figures on plant availability. In addition we survey the international situation, mainly covering developing countries. Generally, the technology is sufficiently mature for commercialization, though some unit operations, for example catalytic tar reforming, still needs further development. Further development and optimization will probably streamline the performance of the various plants so that their biofuel-to-electricity efficiency reaches 30-40 % and overall performance efficiency in the range of 90 %. The Harboøre, Skive, and Güssing plant types are considered appropriate for municipal CHP systems, while the Viking and VIPP-VORTEX plants are smaller and considered appropriate for replacing hot water plants in district heating network. The Danish Technical University (DTU) Biomass Gasification Group and Meva International have identified a potentially large market in the developing countries of Asia. Areas for suggested further research and development include: Gas      cleaning/upgrading Utilization      of produced heat System      integration/optimization Small scale      oxygen production Gas engine      developmentsI ett gemensamt projekt har Linnéuniversitetet i Växjö och Lunds Tekniska Högskola, på uppdrag av Energimyndigheten, genomfört en inventering av teknik och system för småskalig kombinerad värme och kraft produktion via förgasare-gasmotor teknik. Definitionen för småskalighet i denna studie, är anläggningar med en termisk effekt upp till 10 MW(3 MWel) och där bränslet är någon form av biomassa, vanligtvis träbaserad (trä eller skogsavfall) i form av flis, pellets eller spån. Projektrapporten innehåller först en deskriptiv del över teknikens ståndpunkt inom småskalig förgasning, gasrening och gasmotorer. Den andra delen utgörs av en fallbeskrivning för de olika anläggningarna som ingår i studien. MEVA Innovations VIPP-VORTEX CHP anläggning DTU:s VIKING CHP anläggning Bio-kraftverket i Güssing Harboøre CHP anläggning Skive CHP anläggning I fallbeskrivningarna gås anläggningarnas särdrag, funktioner samt enhetsoperationer igenom, samt vilken typ av bränsle som används och vilka verkningsgrader som uppnås. Investerings- och driftskostnaderna, där sådana är tillgängliga, presenteras tillsammans med uppgifter på anläggningarnas tillgänglighet. Även en internationell utblick, huvudsakligen fokuserad på utvecklingsländer, har genomförts.    Generellt sett är tekniken tillräckligt mogen för kommersialisering. Det finns dock en del enhetsoperationer, t.ex. tjärkrackning och tjärreformering, som behöver fortsatt forskning och utveckling. Fortsatt utveckling av systemen kommer förmodligen att göra prestandan för anläggningarna än mera lika och öka elverkningsgraden till 30-40 % med en total verkningsgrad runt 90 %. Harboøre-, Güssing- och Skiveanläggningarna är avsedda som kommunala kraft-värmeanläggningar medan Viking och VIPP-VORTEX är avsedda att ersätta mindre varmvattencentraler i fjärrvärmenätet. Bimass Gasification Group DTU och MEVA Innovation har också identifierat en potentiellt stor marknad i utvecklingsländer i Asien.      Förslag till områden för fortsatt forsknings och utvecklingsarbete: Gasrening/Gasuppgradering Användning av producerat värme System integration/optimering Småskalig syre-produktion Vidareutveckling av gasmotore

Understanding the effect of Intake temperature on the ϕ-sensitivity of toluene-ethanol reference fuels and neat ethanol

The low-temperature combustion (LTC) is an attractive concept that enables the modem combustion engines to move toward sustainability mainly by increasing the efficiency and decreasing the emissions. The modern combustion engines which are working based on the LTC concept have specific fuel requirements. Fuel ϕ-sensitivity is a key factor to be considered for tailoring fuels for these engines. Fuel with a high ϕ-sensitivity are more responsive to thermal or fuel stratifications; the auto-ignition properties of different air-fuel mixtures of these fuels, with different equivalence ratio (ϕ), are more diverse. This diversity provide a smoother heat release rate in stratified condition. In this study 11 different toluene–ethanol reference fuels (TERFs) in three research octane number (RON) groups of 63, 84, and 105 together with neat ethanol are evaluated. The Lund ϕ-sensitivity method is used to evaluate these fuels in a cooperative fuel research (CFR) engine. The effect of variation of intake temperature on pressure sensitivity of fuel at a constant combustion phasing is evaluated. This evaluation is performed at two intake temperature of 373 and 423 K, and the results are compared with the outcome of the Lund ϕ-sensitivity number with the intake temperature of 323 K. This study shows that the CR sensitivity response of different blends to the intake charge temperature variation depends on the fuel composition. Accumulated low temperature heat release and latent heat of vaporization. It proves that the fuel ϕ-sensitivity will vary under different thermodynamic conditions. There was a clear link between the accumulated heat released during the early reaction and CR sensitivity of the blends at different intake temperature of 373 and 423 K but the link with the latent heat of vaporization (HoV) found to be inexplicit

A Review of Isobutanol as a Fuel for Internal Combustion Engines

Isobutanol, one of the four isomers of butanol (C4H9OH), possesses some favorable properties that make it an attractive fuel for internal combustion engines. For instance, when compared to ethanol, isobutanol features a higher heating value and lower hygroscopicity (which prevents corrosion and enables it to be transported via pipelines). Moreover, its addition to gasoline does not distort the fuel blend’s vapor pressure to the same extent as ethanol does. All of this while having a high octane rating. Those advantages over ethanol suggest that isobutanol has the potential to be used as a gasoline oxygenate or even as a neat fuel. Furthermore, the advances made in biotechnology have enabled isobutanol to be produced from biomass more efficiently, allowing it to be used in compliance with existing renewable energy mandates. This article reviews some of the relevant literature dedicated to isobutanol as a motor fuel, covering its merits and drawbacks. Several studies on its combustion characteristics are also discussed. Most of the included literature refers to the use of isobutanol in spark-ignition (SI) engines, as its properties naturally lend themselves to such applications. However, isobutanol’s utilization in diesel engines is also addressed, along with a couple of low-temperature combustion examples

Pressure Sensitivity of HCCI Auto-Ignition Temperature for Oxygenated Reference Fuels

The current research focuses on creating a homogeneous charge compression ignition (HCCI) fuel index suitable for comparing different fuels for HCCI operation. 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. The purpose of this study was to map the AIT and the amount of LTHR of different oxygenated reference fuels in HCCI combustion at different cylinder pressures. Blends of n-heptane, iso-octane, and ethanol were tested in a cooperative fuels research (CFR) engine with a variable compression ratio. Five different inlet air temperatures ranging from 50 degrees C to 150 degrees 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 deg after top dead center (TDC). The experiments were carried out in lean operation with a constant equivalence ratio of 0.33 and with a constant engine speed of 600 rpm. The amount of ethanol needed to suppress the LTHR from different primary reference fuels (PRFs) was evaluated. The AIT and the amount of LTHR for different combinations of n-heptane, iso-octane, and ethanol were charted