Fundamental phenomena affecting low temperature combustion and HCCI engines, high load limits and strategies for extending these limits
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AbstractLow temperature combustion (LTC) engines are an emerging engine technology that offers an alternative to spark-ignited and diesel engines. One type of LTC engine, the homogeneous charge compression ignition (HCCI) engine, uses a well-mixed fuel–air charge like spark-ignited engines and relies on compression ignition like diesel engines. Similar to diesel engines, the use of high compression ratios and removal of the throttling valve in HCCI allow for high efficiency operation, thereby allowing lower CO2 emissions per unit of work delivered by the engine. The use of a highly diluted well-mixed fuel–air charge allows for low emissions of nitrogen oxides, soot and particulate matters, and the use of oxidation catalysts can allow low emissions of unburned hydrocarbons and carbon monoxide. As a result, HCCI offers the ability to achieve high efficiencies comparable with diesel while also allowing clean emissions while using relatively inexpensive aftertreatment technologies. HCCI is not, however, without its challenges. Traditionally, two important problems prohibiting market penetration of HCCI are 1) inability to achieve high load, and 2) difficulty in controlling combustion timing. Recent research has significantly mitigated these challenges, and thus HCCI has a promising future for automotive and power generation applications. This article begins by providing a comprehensive review of the physical phenomena governing HCCI operation, with particular emphasis on high load conditions. Emissions characteristics are then discussed, with suggestions on how to inexpensively enable low emissions of all regulated emissions. The operating limits that govern the high load conditions are discussed in detail, and finally a review of recent research which expands the high load limits of HCCI is discussed. Although this article focuses on the fundamental phenomena governing HCCI operation, it is also useful for understanding the fundamental phenomena in reactivity controlled compression ignition (RCCI), partial fuel stratification (PFS), partially premixed compression ignition, spark-assisted HCCI, and all forms of low temperature combustion (LTC).
CitationSaxena S, Bedoya ID (2013) Fundamental phenomena affecting low temperature combustion and HCCI engines, high load limits and strategies for extending these limits. Progress in Energy and Combustion Science 39: 457–488. Available: http://dx.doi.org/10.1016/j.pecs.2013.05.002.
SponsorsThe authors wish to acknowledge many colleagues in the engine research community for their thoughts and insights regarding the fundamental phenomena discussed in this article. The participants at the bi-annual U.S. DOE Advanced Engine Consortium meetings have provided valuable understanding about low temperature combustion engine technologies. For the fruitful discussions that helped improve the authors' understanding on the topics covered in this article, the authors particularly acknowledge Dr. John Dec at Sandia National Laboratory, Professor Darko Kozarac at the University of Zagreb, Professor Mani Sarathy at King Abdullah University of Science and Technology (KAUST), and Professors Robert Dibble and J-Y Chen at the University of California at Berkeley.Funding to support some of the research topics discussed in this article was provided through the U.S. Department of Energy (through the HCCI/Advanced Engine Consortium), the Natural Sciences and Engineering Research Council of Canada, laboratory directed research and development funds at Lawrence Berkeley National Laboratory, and Programa de Sostenibilidad de Grupos de Investigación 2013–2014 Vicerrectoría de Investigación (Universidad de Antioquia – Colombia).Finally, the authors thank our readers for choosing this article. We welcome any feedback or questions of the topics discussed in this article, or discussion of emerging engine or vehicle powertrain technologies. In particular, we welcome discussions on potential research collaborations to develop engine and powertrain technologies for vehicles of the future.