A numerical study of the effects of IEGR on the set-off auto-ignition in an HCCI engine

The shortcomings of traditional combustion techniques are being continually evaluated and alternate combustion modes are being sought. One such combustion mode that is receiving a lot of attention is Homogenous Charge Compression Ignition (HCCI). HCCI is a combustion process that has the potential to be highly efficient and produces low emissions. It can provide high, diesel-like efficiencies using gasoline, diesel, and most alternative fuels. The major drawback with HCCI is controlling the ignition timing over a wide range of load and speed. The local chemical and thermal conditions of the charge mixture, towards the end of the compression stroke, have significant influences on the set-off auto-ignition. In this paper, numerical study has been carried out to examine the effects of mixture quality on the occurrence of auto-ignition at the end of the compression stroke inside a pentroof combustion chamber. The effect of different Internal Exhaust Gas Re-circulation (IEGR) are investigated. The use of IEGR acts as an indirect control method, the rate of combustion can be slowed down; however the percentage of IEGR retained in the cylinder affects the onset of auto-ignition. The calculated results have been validated against published experimental data, so that the correlation between the two can be discussed. It is found that the inhomogeneity of the air, fuel and the IEGR mixing, presented here in terms of temperature distribution, plays an important role in initiating, and potentially further controlling the HCCI combustion. During the compression process, certain parts of the engine charge are found to reach a higher temperature which auto-ignited depending on the percentages of IEGR used

Elite players’ perceptions of football playing surfaces: a mixed effects ordinal logistic regression model of players’ perceptions

The aim of this study was to determine potential explanatory factors that may be associated with different attitudes amongst the global population of elite footballers to the use of different surfaces for football. A questionnaire was used to capture elite football players’ perceptions of playing surfaces and a mixed effects ordinal logistic regression model was used to explore potential explanatory factors of players’ perceptions. In total, responses from 1129 players from 44 different countries were analysed. The majority of players expressed a strong preference for the use of Natural Turf pitches over alternatives such as Artificial Turf. The regression model, with a players’ country as a random effect, indicated that players were less favourable towards either Natural Turf or Artificial Turf where there was perceived to be greater variability in surface qualities or the surface was perceived to have less desirable properties. Player’s surface experience was also linked to their overall attitudes, with a suggestion that the quality of the Natural Turf surface players experienced dictated players’ support for Artificial Turf

A CFD model with optical validation on in-cylinder charge performances of CAI engines

Over the past few decades, Homogeneous Charge Compression Ignition (HCCI) or Controlled Auto-Ignition (CAI) if it is fuelled with gasoline type of fuels has shown its potential to overcome the limitations and environmental issue concerns of the Spark Ignition (SI) and Compression Ignition (CI) engines. However, controlling the ignition timing of a CAI engine over a wide range of speeds and loads is challenging. Combustion in CAI is affected by a number of factors; the local temperature, the local composition of the air/fuel mixture, time and to a lesser degree the pressure. The in-cylinder engine charge flow fields have significant influences on these factors, especially the local gas properties, which leads to the influences towards the CAI combustion. In this study, such influences were investigated using a Computational Fluid Dynamics (CFD) engine simulation package fitted with a real optical research engine geometry. Applying a Laser Doppler Anemometry (LDA) to the same engine, the cycle averaged time history mean and Root Mean Square (RMS) velocity profiles for the axial and radial velocity components in three axial planes were measured throughout the inlet and compression stroke. The calculated results were compared with the experimental results in terms of the vectors flow fields, averaged integrated tumble ratio as a function of crankangle and the local velocities in this paper. The results from both studies showed good correlations

Elite players’ perceptions of football playing surfaces: A qualitative study

Purpose: The decision by the International Football Association Board in 2004 to approve the use of artificial surfaces in elite football (soccer) competitions remains controversial amongst many players, managers and coaching staff. The aim of this study was to conduct a comprehensive assessment of players’ opinions to better understand the influence of playing surfaces on the game of football and identify factors that may contribute to differences of opinion. Method: Qualitative data were collected from 103 elite footballers and 21 coaching staff during a series of interviews and focus groups. A thematic analysis was conducted to identify patterns in the data. Results: Players considered that the type and condition of a playing surface influenced ball-surface interactions, game play, tactics/strategy, footwear selection, movement, risk of injury and fatigue. Together these influence a player’s perception of the suitability of a surface and also their mindset, which could ultimately affect their performance. Conclusion: The majority of participants in this study expressed a higher preference for natural grass over artificial turf pitches. A perceived increased risk of injury on artificial turf remains a primary concern despite a lack of supporting evidence in research studies. To address this discrepancy, the reporting of muscle soreness and the effect of constant surface switching merit further consideration. Not all participants shared the same views and player characteristics such as age, surface experience, injury history and playing style/position were found to be potential factors that could account for differences in elite players’ opinions regarding the surfaces used in football.</div

A CFD Model with Optical Validation on In-cylinder Charge Performances of CAI Engines

Over the past few decades, Homogeneous Charge Compression Ignition (HCCI) or Controlled Auto-Ignition (CAI) if it is fuelled with gasoline type of fuels has shown its potential to overcome the limitations and environmental issue concerns of the Spark Ignition (SI) and Compression Ignition (CI) engines. However, controlling the ignition timing of a CAI engine over a wide range of speeds and loads is challenging. Combustion in CAI is affected by a number of factors; the local temperature, the local composition of the air/fuel mixture, time and to a lesser degree the pressure. The in-cylinder engine charge flow fields have significant influences on these factors, especially the local gas properties, which leads to the influences towards the CAI combustion. In this study, such influences were investigated using a Computational Fluid Dynamics (CFD) engine simulation package fitted with a real optical research engine geometry. Applying a Laser Doppler Anemometry (LDA) to the same engine, the cycle averaged time history mean and Root Mean Square (RMS) velocity profiles for the axial and radial velocity components in three axial planes were measured throughout the inlet and compression stroke. The calculated results were compared with the experimental results in terms of the vectors flow fields, averaged integrated tumble ratio as a function of crankangle and the local velocities in this paper. The results from both studies showed good correlations