Analyzing of in-cylinder flow structures and cyclic variations of partially premixed combustion in a light duty engine

Partially Premixed Combustion (PPC) strategy offers the potential for simultaneously reduction of NOx and soot emissions with high efficiency. This low temperature combustion strategy involves a proper mixing of fuel and air prior to auto-ignition. During ignition delay (ID) the exact amount of premixing is crucial for the combustion behaviour and emission formation.\u3cbr/\u3eIn this article, high-speed particle image velocimetry (HS-PIV) has been applied to characterise the in-cylinder flow and cycle-to-cycle variations in a light-duty optical engine during fired conditions. The engine is operated at 800 rpm and at a constant CA 50 (~ 8 CAD aTDC). Multiple injections strategies (single, double and triple injections) have been applied to investigate their influence on the flow inside the piston bowl and squish region. The 2D velocity fields are evaluated and investigated over a range of crank angles in the compression and expansion strokes in order to understand the cycle-to-cycle variations. To investigate the problem of cyclic- variations on in-cylinder flows the phase-invariant proper orthogonal decomposition (POD) technique was used. The POD decomposition technique provides a classification method based on an energy criterion by which the mean flow is seen as a superposition of coherent structures. From their temporal coefficients it is possible to characterize its dynamical behaviour

Ignition sensitivity study of Partially Premixed Combustion by using shadowgraphy and OH* chemiluminescence methods

Partially Premixed Combustion (PPC) is a promising combustion concept for future IC engines. However, controllability of PPC is still a challenge and needs more investigation. The scope of the present study is to investigate the ignition sensitivity of PPC to the injection timing at different injection pressures. To better understand this, high-speed shadowgraphy is used to visualize fuel injection and evaporation at different Start of Injections (SOI). Spray penetration and injection targeting are derived from shadowgraphy movies. OH* chemiluminescence is used to comprehensively study the stratification level of combustion which is helpful for interpretation of ignition sensitivity behavior. Shadowgraphy results confirm that SOI strongly affects the spray penetration and evaporation of fuel. However, spray penetration and ignition sensitivity are barely affected by the injection pressure. There is a critical SOI range, in which a significant amount of fuel is trapped in the crevice volume. Injection in this critical range has a negative influence on the combustion efficiency and ignition sensitivity. Impingement of liquid fuel on the piston crown advances the combustion phasing by providing higher levels of stratification. Moreover, results of combustion stratification study show that stratification level has an inverse correlation with combustion phasing of PPC for late injections

Combustion stratification study of partially premixed combustion using Fourier transform analysis of OH* chemiluminescence images

A relatively high level of stratification (qualitatively: lack of homogeneity) is one of the main advantages of partially premixed combustion over the homogeneous charge compression ignition concept. Stratification can smooth the heat release rate and improve the controllability of combustion. In order to compare stratification levels of different partially premixed combustion strategies or other combustion concepts, an objective and meaningful definition of “stratification level” is required. Such a definition is currently lacking; qualitative/quantitative definitions in the literature cannot properly distinguish various levels of stratification. The main purpose of this study is to objectively define combustion stratification (not to be confused with fuel stratification) based on high-speed OH* chemiluminescence imaging, which is assumed to provide spatial information regarding heat release. Stratification essentially being equivalent to spatial structure, we base our definition on two-dimensional Fourier transforms of photographs of OH* chemiluminescence. A light-duty optical diesel engine has been used to perform the OH* bandpass imaging on. Four experimental points are evaluated, with injection timings in the homogeneous regime as well as in the stratified partially premixed combustion regime. Two-dimensional Fourier transforms translate these chemiluminescence images into a range of spatial frequencies. The frequency information is used to define combustion stratification, using a novel normalization procedure. The results indicate that this new definition, based on Fourier analysis of OH* bandpass images, overcomes the drawbacks of previous definitions used in the literature and is a promising method to compare the level of combustion stratification between different experiments.\u3cbr/\u3e\u3cbr/\u3

Fuel and combustion stratification study of Partially Premixed Combustion

Relatively high levels of stratification is one of the main advantages of Partially Premixed Combustion (PPC) over the Homogeneous Charge Compression Ignition (HCCI) concept. Fuel stratification smoothens heat release\u3cbr/\u3eand improves controllability of this kind of combustion. However, the lack of a clear definition of “fuel and combustion stratifications” is obvious in literature. Hence, it is difficult to compare stratification levels of different PPC strategies or other combustion concepts. The main objective of this study is to define the fuel and combustion stratifications based on the fuel tracer LIF and OH* chemiluminescence images, respectively. A light duty optical engine has been used to perform the measurements. Four experimental points are evaluated, with injection timings in both the homogeneous and the stratified regimes. Twodimensional Fourier transforms of fuel distribution and chemiluminescence images provide the range of spatial frequencies in these images. This method gives the opportunity to separate a specific range of frequencies related to fuel and combustion stratification. The signal energy content in this range is used to define the stratification, using an appropriate normalization procedure. The results indicate that this new definition is a promising method to compare the level of stratification between different experiments

Keeping their heads down: Shame and pride in the stories of Protestants in the Irish Republic

This study draws on a number of in-depth interviews to explore the ethnic aspect of Protestantism in the Republic of Ireland. We explore themes of shame and pride around issues of identity, together with a sense of loss of a minority rapidly losing cultural distinctiveness. Following Ireland‘s division, the ordinary Protestants of the south, comprising a range of religious denominations bound by history, intermarriage and culture, found themselves in a society in which their story was rarely told. The dominant narrative was one of a Catholic people, long oppressed by a wealthy Protestant minority. The story of ordinary Protestants, including those in rural and urban poverty, went largely unheard. Today, ordinary Protestants – small farmers, shop keepers, housewives – tell the story of Ireland as seen through their family‘s narratives. Themes of pride and shame, often intertwined, form a thread that binds their testimony, drawing on family, personal and local history, folklore and statements of identity

Time-resolved in-cylinder PIV measurement in a light duty optical engine under PPC conditions

The understanding of in-cylinder flow field is one of the keys to realize Partially Premixed Combustion (PPC) for internal combustion engines, which has potential to achieve high combustion efficiency with low soot and NOx emissions. In this work, time resolved Particle Image Velocimetry (PIV) was performed to measure the flow field inside the cylinder of a single-cylinder light-duty optical diesel engine.\u3cbr/\u3eThe engine was modified to Bowditch configuration, and was installed with a quartz piston and a transparent cylinder liner, to allow optical access. The geometry of the quartz piston crown is based on the regular combustion chamber design of mass produced diesel engine, including a re-entrant bowl shape. This causes severe distortion on the obtained images, which has to be handled by a distortion correction method before PIV process.\u3cbr/\u3eThe in-cylinder flow structures in a vertical plane at the center of cylinder were obtained both within the piston bowl and within the squish volume, during the compression and expansion stroke. Measurements were performed under three different injection strategies as well as motored engine condition. Both the instantaneous flow field from single cycle and ensemble average flow field calculated from 100 cycles at motored engine condition show a well match with previous studies. The results from fired engine conditions show different Interaction between injected fuel and in-cylinder air at different Crank Angle Degrees (CADs) with different injection strategies.\u3cbr/\u3eAll the results in this study can provide a quantitative dataset being useful to model validation of numerical simulation work to investigate PPC engine more

Effects of injection timing on fluid flow characteristics of partially premixed combustion based on high-speed particle image velocimetry

Partially premixed combustion (PPC) is a promising combustion concept to meet the increasing demands of emission legislation and to improve fuel efficiency. Longer ignition delay of PPC in comparison with conventional diesel combustion provide better fuel/air mixture which decreases soot and NOx emissions. Moreover, a proper injection timing and strategy for PPC can improve the combustion stability as a result of a higher level of fuel stratification in comparison with Homogeneous Charge Compression Ignition (HCCI) concept. Different injection timings affect this level of fuel and combustion stratification which helps to control the combustion timing and the heat release behavior. The scope of the present study is to investigate the fluid flow characteristics of PPC at different injection timings. To better understand this, high-speed Particle Image Velocimetry (PIV) is implemented in a light duty optical engine to measure fluid flow characteristics inside the piston bowl as well as the squish region with a temporal resolution of 1 crank angle degree at 800 rpm. Combustion phasing is kept constant for different injection timings and flow behavior including the mean velocity, turbulent kinetic energy and cycle-resolved turbulence during the injection and combustion phenomena are measured. Two different injectors with 5 and 7 holes are also compared to see their effects on fluid flow and heat release behaviors. Formation of the vortices and turbulence enhance the air fuel interaction, changing the level of fuel stratification and combustion duration. Results well demonstrate how these different turbulent kinetic energies can correlate with heat release behaviors. Furthermore, the research provide a quantitative dataset for validation of numerical simulations