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automotive exhaust emissions and energy recovery

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Since the invention of the first commercially successful internal combustion  (IC) engine by Nikolaus Otto and Eugen Langen in 1866, the  ICE  has remained the most significant and widely used form of energy  conversion technology  in the transportation  sector.

 Throughout the years, IC engines have  been principally   diversified by type of fuel, type of fuel injection and  combustion  mixing  process  as  well  as  through  the  type  of  air  handling  and  exhaust energy recovery  technology used and improvements  have made it more efficient and reliable. 

However,  years  of  air  pollution  as  a  result  of  emissions  from  IC  engines  have  made  the development  and  integration  of  exhaust  emissions  mitigation  technologies  and  systems increasingly  significant  in  the  continued  effort  to  provide  engines  to  the  market  which conform to increasingly stringent emissions regulations. ICE  development has to take into account air pollutants  such as Nitrogen Oxides  (NOx), Carbon  Monoxides  (CO)  and  Hydrocarbons  (HC),  particulate  matter  (PM)  as  well  as greenhouse gases (GHG) such as Carbon Dioxide (CO2) and Nitrous Oxide (N2O).

 In Europe, for example, Euro1 introduced in 1992 is the first of many  subsequent EU  regulations  which regulates  air  pollutants.  In  2009,  the  European  Commission  brought  about  mandatory  CO2 emission  targets to regulate the new passenger car fleet CO2 emissions at 130 g/km by 2015 and  95  g/km  by  2020.  Emissions  regulations  require  the  mitigation  of  certain,  previously unregulated emissions posing a health risk such as Nitrogen Dioxide (NO2), ammonia as well as  the  formation  of  GHGs.

  New  legislation  is  now  including  limits  for  NH3  and  certain specialist applications have been required to cap NO2 and N2O. Another immediate concern for improved engine efficiency and fuel economy includes customer demand  to own and drive more fuel efficient vehicles. This market-driven demand places additional pressure towards the development of more efficient engines in addition to emissions  mitigation  requirements  and  has  resulted  in  a  proliferation  of  systems  and technologies  in  the  exhaust  system  of  the  IC  engine  to  recover  the  significant  levels  of exhaust gas energy expended after the combustion/power stroke.

 These include new forms of turbocharging, turbocompounding and waste heat recovery technologies. The above driving concerns for fuel economy and reduced emissions make the topic of emissions  control  and  exhaust  energy  recovery  a  timely  one  for  both  gasoline  and  diesel engines.  Whereas  diesel  engines  have  been  predominantly  turbocharged  only  a  relatively small  percentage  of  gasoline  engines  is  similarly  equipped  (especially  in  the  US  and  large Asian markets) which has led  towards  significant efforts  by  engine manufacturers in recent years  to  downsize  and  downspeed  these  engines.

  On  the  other  hand,  the  relative  focus  in diesel  engine  development  in  terms  of  emissions  and  exhaust  energy  recovery  has  shifted towards devices other than the turbocharger for enhanced energy recovery and in emissions control technologies to allow the diesel engines of the future to keep up with the twin demand for very low emissions and increasing levels of fuel economy.

 The present volume on “Automotive Exhaust Emissions  and Energy Recovery”focusses, therefore,  on  the  exhaust  system  and  on  the  technologies  and  methods  used  to  reduce emissions and increase fuel economy by capitalising upon the exhaust gas energy availability (either in the form of gas kinetic energy or as waste heat extracted from the exhaust gas). 

It is projected  that  in  the  short  to  medium  term,  advances  in  exhaust  emissions  and  energy recovery technologies will lead the way in IC engine development and pave the way towards increasing  levels  of  engine  hybridisation  until  full  electric  vehicle  technology  can  claim  a level of maturity and corresponding market share to turn the bulk of this focus away from the ICE. 

The book is comprised of ten chapters which in most cases provide a review of recent developments as well as future directions for both gasoline and diesel four-stroke engines. As such  the  present  volume  is  aimed  at  engine  research  professionals  in  the  industry  and academia in the first place but also towards students of powertrain engineering.

 The collection of articles in this book aims to review both fundamentals of relevant, recent exhaust system technologies  but  to  also  detail  recent  or  on-going  projects  and  to  uncover  future  research directions and potentials where relevant. The content is not divided in sections but individual chapters follow the approximate route of  the exhaust gas from in-cylinder formation in the initial chapters to waste  heat  recovery  technologies at the end with discussion on bio-fuels included where relevant. The initial chapter run of six chapters is principally dedicated to the emissions (mitigation and control) part of the book. 

Chapter 1 starts off with a description and review of emissions mitigation and control systems for both gasoline and diesel engines. The systems covered are three-way-catalysts, exhaust gas re-circulation (EGR), oxidation catalysts, particulate filters, selective  catalytic  reduction  (SCRs)  and  leanNOx trap  designs  as  well  as  water  injection systems. 

 Diesel  in-cylinder  NOx and  soot  formation  by  means  of  optical  techniques  is investigated in Chapter 2 for rapeseed methyl ester (RME) combustion. Further to the topic of NOx,  the  influence  of  different  EGR  rates  to  diesel  engine  emissions  is  experimentally investigated and presented in Chapter 3. 

Chapter 4 is a review of literature on the effects of biofuel/diesel  blends  on  particulate  matter  (PM)  emissions  from  diesel  engines  operating under transient conditions and a statistical analysis allows comparisons to be drawn for the different types of fuel.

 Chapter 5 is a review of aftertreatment technologies with the provision of  not  only  the  physico-chemical  phenomena  and  the  respective  mathematical  modeling equations describing the transport and reaction processes but moves beyond the discussion of Chapter  1,  also,  in  that  it  focusses  on  system  design  challenges  from  the  control  and optimisation  points  of  view.  

Chapter  6,  concludes  the  initial  chapter  run  on  in-cylinder measurements and aftertreatment technologies by focussing exclusively on Diesel Particulate Filters (DPFs); the chapter is a review of DPFs with a focus on filter material choices and the wall flow DPF design considerations. The final chapter run of four chapters focusses on exhaust (both mechanical and thermal) energy recovery technologies and its impact on fuel economy (as well as emissions). 

Chapter 7  is  a  review  of  turbocharging  technology,  covering  fundamentals  as  well  as  engineturbocharger matching and applications of such systems in modern use. Chapter 8, focusses on small, high power density, directly  injected (DI), turbocharged engines which are of wide interest  given  the  industry’s  focus  of  today  on  downsized,  turbocharged,  SI  engines.  This chapter  reports  on  the  trends  in  the  turbo-gasoline  DI  technology  and  includes  the implications from the use of three way catalytic converter aftertreatment for energy recovery and fuel economy while complying with pollutant emissions standards. The final two chapters review  waste  heat  recovery  technologies  most  recently  introduced  in  the  product  range  of several  manufacturers.  Chapter  9  focusses  on  automotive  Organic  Rankine  Cycle  (ORC) applications  from  the  point  of  view  of  the  design  challenge  associated  with  process component design  (mainly of the expander in small scale systems)  due to the  low IC  engine waste heat power  availability  and further challenges  associated with the restricted available space  for  the  process  heat  exchangers. 

 The  concluding  chapter  (no.10)  is  a  review  of technologies associated with mechanical as well as hybrid  (electric) exhaust energy recovery systems,  as  well  as  of  most  waste  heat  recovery  technologies  currently  in  development including  the  development  of  systems  based  on  Bottoming  (including  Rankine)  Cycles  as well as Thermoelectric generator systems.

 This book has been made possible by the dedication of contributing authors to agree to and to then proceed to complete their works within the agreed, final publication schedule, for which I am grateful. I would also like to thank Carra Feagaiga and the staff of NOVA Science Publishers for their professional support in preparing this book.