Influence of the Velocity Near the Spark Plug on Early Flame Development

The objective of this paper is to investigate how the velocity and turbulence within different locations close to the spark plug influence the combustion at individual cycles in a SI-engine. 2-D cycle-resolved laser doppler velocimetry (LDV) measurements have been done both inside the spark gap and around the spark tip to extract velocity information. The pressure in the cylinder was measured with a piezo-electric transducer connected to an A/D-card in a standard PC. The velocity information was filtered to get "mean velocity" and "turbulence". The pressure signal was used in a one-zone heatrelease model to get different levels of mass fraction burned etc. The results show a significant influence of both the "mean velocity" and the "turbulence" on the early part of the combustion when the velocity was measured close to the spark plug tip. The influence was less significant when the velocity was measured at some distance from the electrodes for both a pancake and a high squish combustion chamber. The correlation between the velocity close to the spark plug and the early flame development showed no dependence on the air-fuel ratio and a modest dependence on ignition timing

Renewable energy, energy security and resilient societies

Abstract in UndeterminedSometimes energy security is used as an advocacy for renewable energy systems. Although renewable energy systems can surely have such characteristics they will not per se solve all types of security problems, and new problems will most certainly arise. In this paper, energy security aspects of renewable energy systems are analysed taking the starting point in a broad typology on energy security. Various renewable energy systems will be discussed from an EU perspective, however noticing the on-going development of global renewable energy markets. Three specific areas will be discussed more thoroughly: the expansion of biofuels, the integration of large quantities of variable electricity in the electricity system, and the existing plans for providing significant parts of renewable electricity from Northern Africa. Furthermore, the importance of various institutions is touched upon

DC-DC Converters - Dynamic Model Design and Experimental Verification

To obtain high performance control of a dc-dc converter, a good model of the converter is needed. The load usually affects the dynamics and one way to take this into consideration is to regard the load as a part of the converter. The load is often the most variable part of this system. If the load current and the output voltage are measured there are good possibilities to obtain a good model of the load on-line. Adaptive control can then be applied to improve the control. In peak current-mode control, the output voltage and the inductor current are measured and utilized for control. In the author's licentiate thesis, analytic models were derived for the case where the load current is also measured and utilized for control. The control-to-output transfer function, the output impedance, and the audio susceptibility were derived for the buck, boost, and buck-boost converters operated in continuous conduction mode in the case of resistive load. The use of load current can be seen as gain scheduling in the case where the load is a resistor. Gain scheduling can be considered a special case of adaptive control. The majority of the results in the licentiate thesis were validated by comparing the frequency responses predicted by the analytic models and switched large-signal simulation models. In this thesis, additional results are presented for the buck converter. Experimental results obtained by means of a network analyzer verify the derived control-to-output transfer function and the audio susceptibility but not the output impedance at low frequencies. In the experimental buck converter there are stray resistances in the inductor, transistor, and diode but these stray resistances were not considered in the licentiate thesis. A new transfer function for the output impedance is derived where these stray resistances are considered and it is in good agreement with the experimental result also at low frequencies. If the current to the output capacitor is measured in addition to the output voltage and the inductor current, the load current can be calculated as the difference between the inductor and capacitor currents in the case of the buck converter. Hence, the measurement of the load current can be replaced by measurement of the capacitor current. If this possibility is utilized and the capacitor current is measured by means of a current transformer, a low-frequency resonance is introduced in the frequency responses according to experimental results. The reason for this resonance is due to the high-pass-filter characteristics of the current transformer. A new analytic model is derived which predicts the resonance

Slutrapport från Nätverket för juristutbildning

Vad gäller resultat av satsningen är det svårt att så här tidigt peka på något särskilt. Att vi fått detta stöd har varit en uppmuntran till att fortsätta samarbetet. Det har underlättat att vi fått detta stöd sedan vi genomfört dekan-och prefektmötena två gånger om året. Kostnaderna för denna typ av utbyte brukar inte skena iväg men på marginalen är varje tillskott välkommet i en eljest stram budget. Vi har funnit en väldigt god plattform för att fortsätta arbetet. Mötena har präglats av en god samstämmighet såväl vad gäller juristutbildningen som utbildningen på forskarnivå. Vad gäller den sistnämnda kan framförallt pekas på diskussionerna om den långa studietiden och avhandlingarnas omfattning där vi uppnått enighet även om resultatet låtit vänta på sig. Vad gäller juristutbildningen har, även om våra utbildningar har olika upplägg både innehållsmässigt och vad gäller pedagogiken, utbytet framförallt varit att vi fått idéer från varandra om hur vi skall kunna bli ännu bättre