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Advances in internal combustion engines and fuel technologies

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Over the last decades, there is increasing pressure worldwide for more efficient and envi‐ ronmentally sound combustion technologies that utilise renewable fuels to be continuously developed and adopted. New fuels and combustion technologies are designed to deliver more energy-efficient systems which comply with stringent emission standards and at the same time diversify the dependence on petroleum fuels.

 Set against this background, the central theme of the book is two-fold: advances in internal combustion engines and ad‐ vanced fuel solutions for combustion systems. 

The aim here is to allow extremes of the theme to be covered in a simple yet progressive way. Internal combustion engines remain as the main propulsion system used for ground trans‐ portation, and the number of successful developments achieved in recent years is as varied as the new design concepts introduced. It is therefore timely that key advances in engine technologies are organised appropriately so that the fundamental processes, applications, insights and identification of future developments can be consolidated. 

Here, recent innova‐ tions in spark-ignition engines and compression-ignition engines are reviewed, along with the latest approaches in fuelling, charge preparation and operating strategies designed to further boost fuel economy and level of emissions reduction.

 In the future and across the developed and emerging markets of the world, the range of fuels used will significantly in‐ crease as biofuels, new fossil fuel feedstock and processing methods, as well as variations in fuel standards continue to influence all combustion technologies used now and in coming streams.

 This presents a challenge requiring better understanding of how the fuel mix influ‐ ences the combustion processes in various systems. Here, alternative fuels for automotive engines, gas turbines and power plants in various configurations and designs are appraised. 

The chapters have been written by the contributing authors with the intention of providing detailed description of the latest technological advancements in their respective areas of ex‐ pertise.

 I must personally thank all the authors for their professionalism while preparing this book. I am also delighted to be working alongside Ms. Natalia Reinic on this project. I hope that this book will serve as an excellent read for students, academics and industrial practitioners alike.

In the context of a Spark Ignition engine, the inherent complexity of premixed combustion is exacerbated by a range of engine variables that render the process highly transient in nature and not fully predictable. The present work aims to contribute to the continuous research effort to better understand the details of combustion and be able to model the process in gasoline SI engines. 

Coexisting fossil fuels depletion and environmental concerns, along with an alarming connection between traditional internal combustion engines emissions and human health degradation, have in recent years driven a strong research interest upon premixed SI combustion of energy sources alternative to gasoline, including liquid alcohols like ethanol, and gaseous fuels like hydrogen. However, the advancements enjoyed by gasoline-related technology and infrastructure in the last 40 years have eroded the potential advantages in efficiency and emissions offered by alternative fuels , and the SI engine running on gasoline continues to be the most common type of power unit used in passenger cars (Port-Fuel Injection gasoline engines accounted for the vast majority (91%) of all light-duty vehicle engines produced for the USA market in 2010 ).

The premixed, homogeneous charge gasoline combustion process in SI engines is influenced by the thermo-chemical state of the cylinder charge. Significant factors are local temperature and pressure, stoichiometry and the contents of burned gas within the combustible mixture; these quantities affect rate of burning and consequent in-cylinder pressure development. The combustion process is also greatly influenced by cylinder bulk motion and micro-scale turbulence. Understanding the connection between charge burn characteristics and relevant engines operating variables in the context of modern technologies is extremely useful to enable and support engine design innovation and the diagnosis of performance. 

The present chapter explores the evolution of the combustion process in modern-design gasoline engines, as indicated by the cylinder charge Mass Fraction Burned variation and combustion duration, and the most relevant factors influencing these. It also explores the use, accuracy and limita‐ tions of recently-proposed empirical, non-dimensional (or simplified thermodynamic) combustion models which respond to the requirements of fast execution within model-based control algorithms, and discusses relevant results, which entail the use of Variable Valve Timing systems. 

An exemplar simplified quasi-dimensional models is also presented at the end of the chapter, along with some relevant results concerning an application to flexible fuel, gasoline/ethanol operation. All the experimental data and models discussed here refer and are applicable to stable combustion, typically identified by a Coefficient of Variability of the Indicated Mean Effective Pressure (CoV of IMEP) smaller or equal to 6% [6]. Although the importance of cycle-by-cycle variability is acknowledged, as this may arise from highly diluted combustion, the topic of unstable combustion has not been the focus of the present work.