Modeling of a heavy duty diesel engine to ease complex optimization decisions

Engine optimization becomes more difficult every day, more and more limits regarding emissions of noxious components have to be met. Considering heavy duty marine engines such as the 6DZC from ABC there are several important instances: IMO III reduces NOx by 75% from 2021, EPA reduces NOx by 70% from 2016. Therefore very complex systems are implemented, which each have multiple calibration or working parameters. Some are fixed, some can change depending on engine load and speed. An example of a fixed parameter is compression ratio, it can only be changed while building the engine. Other fixed parameters include: choice of injection nozzle (#holes, hole-diameter), bore, stroke, etc. Exhaust gas recirculation (EGR) is a parameter that can be changed continuously during operation of the engine. Typically there are other parameters present: Variable Valve Timing, injection timing, injection duration, injection pressure, secondary injection, wastegate setting(s), etc. Ideally these parameters are configured in a way that the engine emits very little harmful components and fuel consumption is very low. The most straightforward approach would be to test every parameter combination, record emission components and fuel consumption and choose the optimal parameter combination. This has to be repeated for every speed and load of the engine, which results in an engine map. This method becomes more and more expensive, both in time as in fuel consumption because every additional operating parameter increases the amount of tests exponentially. This is why engine simulation becomes inevitable. Accurate engine simulation is able to exclude regions of parameter values that are clearly infeasible and can give a good indication where engine tests are more interesting

Temporal invariance in repeated cross-sectional 'fear of crime' research

‘Fear of crime’ research is gradually outgrowing the tenacious criticism of being caught within a conservative methodological frame, inherent to the era when the research tradition originated. Over time, the idea that ‘fear of crime’ can be measured in a reliable and valid way by using a single indicator has been questioned. However, using more advanced measures confronts the research tradition with ‘new’ issues related to measurement error, and therefore urges methodological novelty and sophistication to a field notoriously starved of both. Previously, we provided evidence that in order for cross-cultural comparisons to be meaningful, the instruments used to measure ‘fear of crime’, need to exhibit adequate cross-cultural equivalence. This contribution argues that comparing ‘fear of crime’ levels across time is bound to this logic as well. Considering the growing attention paid in recent years to crime, insecurity and ‘fear of crime’ within public opinion in Belgium, as in Western Europe and in an international context in general, it is not unlikely that respondents have indeed changed or are changing their understanding of the issue. Using structural equation modelling (LISREL), this issue of potential temporal invariance or item parameter drift in ‘fear of crime’ item sets, will be assessed in two large scale, repeated cross-sectional research projects in Belgium, Le. the Safety Monitor and the APS-survey. </jats:p

Medium speed diesel engines operated on alternative fuels: lessons learned and remaining questions

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<title>Increased lumens per etendue by combining pulsed LEDs</title>

Led based projectors have numerous advantages compared to traditional projectors, such as: compact, larger color gamut, longer lifetime, lower supply voltage, etc. As LED's can switch rapidly, there is the possibility to pulse. However, there is also an important disadvantage. The optical power per unit of etendue of a LED is significantly lower than e.g. an UHP-lamp (approximately 50 times). This problem can be remedied partly by pulsing of the LED's. If one drives a LED with a pulsed current source, the peak luminance can be higher, albeit that the average luminance will not increase. By pulsing X LED's alternately, their increased flux can be added up in time and will generate a higher average flux within the same etendue. This can be carried out in a number of different configurations. The first configuration uses moving components where a number of LED's (e.g. 8) are mounted on a carrousel and consecutively the pulsed LED is brought in the light path of the projector to fill tip the time with its peak flux. An alternative without moving components can be reached with 2 LED's which are combined with a PBS. By alternately pulsing the LED's with 50% duty cycle and changing the polarisation of one LED with a switchable retarder, one can combine the flux of both LED's in the same etendue. Because of its fast switching time ferro-electric retarders are used here. This can be extended further to 4,8,16... LED's, at the price of a larger and more complicated optical architecture