Advanced Combustion for Sustainable Transport

Research in the IC Engines domain is directed towards novel combustion technologies to improve engine efficiency and reduce harmful pollutants. Technologies are also being developed to adopt alternative, cleaner fuels that meet stricter emission norms globally and reduce dependence on conventional fuels. This book covers various engine combustion technologies under development globally. The first section of the book introduces the combustion technologies being developed for internal combustion engines and has one chapter. In second section, strategies for clean diesel combustion are covered, which would help automotive OEMs continuously improve existing engine technologies. Recent advances in low-temperature combustion (LTC) techniques in CI engines such as Reactivity controlled compression ignition (RCCI), Premixed charge compression ignition (PCCI), Homogeneous Charge Compression Ignition (HCCI), Gasoline compression ignition (GCI) are comprehensively covered. For improving the understanding and control of these LTC techniques, different stages of combustion in LTC regimes are also discussed threadbare. The third section comprehensively discusses optimisation for various control parameters in gasoline direct injection (GDI) engine development. Experimental optical investigations of in-cylinder processes are covered for a superior understanding of fundamental processes. In the fourth section, dual-fuel combustion technology in IC engines is covered since the research interest of the global research community is converging towards fuel diversification. The fifth section includes miscellaneous areas. It discusses the different aspects of metal hydride technology for hydrogen storage, which will help realise hydrogen-fueled vehicles in future. Also, a description of waste heat recovery potential from IC engines using the organic Rankine cycles (ORC) is covered. The information covered in this book would be useful for students, researchers, academicians and the automotive researchers in industry alike.

Diesel engines have been dominant powerplants for transporting goods and public transport, powering agricultural machines as well as industrial machines. After hundred years of evolution, these machines continue to be the most efficient among their counterparts. A practical vision and unbiased analysis would conclusively prove that diesel engines are here to stay for long. Over the years, technology has evolved to meet the demands of customers and policymakers. Fuel efficiency has improved significantly along with the reduction in noise to near-zero levels. An order of magnitude reduction in NO_x and PM has been achieved in the last couple of decades. Future fuels and advanced combustion technology are pioneering the clean diesel revolution. However, the efficiency of conventional diesel combustion (CDC) engines should not be compromised. Therefore, modern-day engine developers need to appreciate the challenges faced in the past and how they have been resolved. This chapter summarises the fundamental causes of in-efficiency, pollutant formation, and possible approaches to tackle them. The chapter also focuses on the technological evolution of diesel engines, modern designs, and strategic optimization trends.

Low temperature combustion (LTC) modes offer high thermal efficiency and low engine-out NOx and soot emissions. The common LTC modes include homogeneous charge compression ignition (HCCI), partially premixed charge compression ignition (PPCI), and reactivity-controlled compression ignition (RCCI). To realize these promising LTC modes, optimal combustion control of the engine in each LTC mode is required. This will require precise control of combustion phasing and engine load, while constraining engine variables including peak in-cylinder gas pressure, maximum pressure rise rate, high intensity ringing or knock, and coefficient of variation of indicated mean effective pressure (IMEP) to allow safe and stable combustion. This chapter explains state-of-the-art of LTC engine control, including dynamic modeling, model predictive combustion control, experimentation, and implementation of real-time closed loop combustion controllers. A well-recognized limitation of LTC engines is a constrained optimal operating range. To this end, multi-mode engines are desired. These include (i) multi-mode LTC engines with mode transition among LTC modes, e.g., dual mode HCCI-RCCI engine, or triple mode HCCI-PPCI-RCCI engine, and (ii) multi-mode engines including LTC and conventional combustion modes, e.g., dual mode HCCI-SI (spark ignition) engines or dual mode RCCI-CDC (conventional diesel combustion) engines. These demands for innovative combustion controllers that capture the engine transient dynamics such as in-cylinder air–fuel ratio variations or residual gas temperature variations during mode transitions. This chapter introduces multi-mode LTC engines and explains controller development for these engines.

The need for higher thermal efficiency, lower NOx and Particulate Matter (PM) emissions has attracted researchers to modify the conventional combustion in IC engines. The after-treatment devices are deployed to meet the emission regulations but they have high initial and maintenance costs. The NOx emissions increase at higher temperatures in the conventional combustion in diesel engines, thus, the researchers are inclined towards finding low-temperature combustion techniques (LTCT). The Homogenous Charge Compression Ignition (HCCI), Reactivity Controlled Compression Ignition (RCCI), and Premixed Charge Compression Ignition (PCCI) are some well-known LTCTs to reduce the NOx to nearly 85%, PM emissions to almost 95%, and can reduce fuel consumption to approximately 15%. The chapter thoroughly reviews the emission performance, combustion characteristics, and thermal efficiency of HCCI, RCCI, and PCCI technologies and makes a comparative analysis of their applications for dual fuel and single fuelled engines. The present study focuses on deriving coherence between the aforesaid advanced combustion technologies’ emission performance with the Euro VI emission norms.

Global concerns about depleting fuel reserves, environment degradation, and sustainability have motivated researchers to explore advanced combustion strategies. In this regard, low-temperature combustion (LTC) has emerged as a promising combustion strategy that can simultaneously reduce soot and NOx emissions with the additional benefit of superior fuel economy. However, researchers must address its primary challenges, w.r.t. controlling ignition timing, combustion phasing, and high heat release rate (HRR), to practically implement it on a large scale. Partially premixed compression ignition (PPCI) is a type of LTC that can address these drawbacks. In PPCI, the injection is closer to ignition when compared with homogeneous charge compression ignition (HCCI), which provides superior control over the ignition. It achieves better mixing and low in-cylinder temperatures using medium to high exhaust gas recirculation (EGR) levels. Optical diagnostics are powerful tools used by researchers to understand the physical behaviour of these complex processes in engines or engine-like conditions. The main attempt of this chapter is to summarize the understandings obtained by researchers about the two-stage combustion occurring in PPCI conditions using optical diagnostics. In the build-up, a brief introduction is given to the conventional diesel combustion (CDC) model and the chemical kinetics involved in the LTC to provide an overall understanding.

Rising regulatory demand around the world for lower exhaust pollutants and reduced greenhouse gas emissions in the commercial transport and passenger car sectors motivates the development of highly efficient and clean internal combustion engines. In recent years, by harnessing gasoline’s low autoignition reactivity and unique spray characteristics, gasoline compression ignition (GCI) has shown the potential as a cost-effective engine technology to achieve high fuel efficiency with low engine-out NOx and soot emissions. This chapter began with an overview of gasoline’s autoignition behavior and spray characteristics. Then, building on an-in-depth understanding of the fundamental gasoline combustion knowledge, the basic principles, benefits, and challenges of varying GCI combustion strategies were discussed based on the level of in-cylinder fuel stratification, encompassing homogenous charge compression ignition (HCCI), partially-premixed compression ignition (PPCI), and mixing-controlled compression ignition (MCCI). To reach the full performance potential for GCI, it is essential to develop tailored combustion and air-handling system concepts. Harnessing these learnings, recent efforts towards developing advanced, production-intent heavy-duty and light-duty GCI engines were reviewed. Finally, the benefits and the key technical areas for commercializing GCI engines were reviewed.

Advancements in internal combustion (IC) engine technologies have improved both spark ignition (SI) and compression ignition (CI) engines immensely in terms of fuel efficiency and emissions. Gasoline engines are giving tough competition to their diesel counterparts in the light-duty passenger car segment with continuously increasing market share. Apart from lower exhaust emissions, current generation Gasoline Direct Injection (GDI) engines offer higher power output and superior fuel economy. Nevertheless, automotive researchers and engineers have used many tools to evolve state-of-the-art GDI engine technology continuously. The most important and useful tool in engine development is optical diagnostics. Optical access to the engine allows non-intrusive investigations of the in-cylinder processes using optical/laser-based diagnostics, which provides information not available by any other research tool. This chapter discusses applying such techniques to understand various in-cylinder processes such as spray-flow interactions, fuel–air mixture formation, combustion, and pollutant formation in GDI engines. It includes detailed perspectives that help optimize engine design and control parameters adapted to conventional and alternative fuels. It broadly covers studies related to in-cylinder flow characteristics, sprays characterization, fuel spray-air interactions, fuel evaporation, mixture formation, flame propagation characteristics, and pollutant formation, corresponding to different GDI engine operating parameters. This chapter discusses applications of various optical diagnostic techniques in GDI engine investigations such as particle imaging velocimetry (PIV), Mie-scattering, phase Doppler interferometry (PDI), laser-induced fluorescence (LIF), natural flame chemiluminescence, laser-induced incandescence (LII), OH/CH chemiluminescence. The rich information derived from the optical diagnostic techniques helps develop new-generation GDI engines capable of meeting market requirements and emission compliance.

The quest for a sustainable future for transport-fuels has led to the consideration of advanced methods of admixing fossil fuels without compromising their qualities; this is aimed at improving/complementing the properties of these fuels for high engine performance. Owing to the high abundance of biomass from which alternative fuels can be sourced for blending or improving the properties of conventional gasoline and diesel fuels, it has become pertinent to consider their use as complementary fuels towards ensuring high sustainability of the fuels as transport-fuels. The synergistic effects offered by these fuels helps to improve the properties of the fuels better than the individual components that make up the fuel mix. Hybrid gasoline-biofuel fuels offer these improved properties as a result of the complementary effects of either or both components offer in the hybrid fuels such that there is a boost in the fuel’s combustion potential owing to the degree of homogenization attained during blending. Furthermore, despite ensuring high compatibility of the individual fuels that make up the biofuel-diesel fuel mix, it is also pertinent to emphasize the need to obtain an optimum blend of the dual fuel system for the engine performance because, for specific dual fuel systems, beyond the optimum mixture composition, the performance of the engine begins to wane owing to the alteration in the properties of the fuel mix beyond favorable conditions for complete/near complete combustion of the fuels. Therefore, in this chapter, the properties of different dual fuel systems will be discussed alongside the degree of homogenization that can improve the atomization/combustion potential of the fuels towards attaining high engine BTEs, high engine power, moderate heat release rates as well as good air–fuel ratios.

Unrestrained consumption of petroleum products and harmful emissions generated from them are of great concern globally. Because of stringent emission legislation, researchers are now focusing on controlling emissions and performance improvement in the existing vehicles. Dual-fuel operation using CNG is an option for emission compliance while improving fuel economy. The dual-fuel mode can be used in both compression ignition (CI) and spark ignition (SI) engines, with gaseous fuel (compressed natural gas: CNG) being the primary fuel and a small proportion of liquid fuel being injected as pilot fuel (Secondary fuel). Due to vast availability, cleaner combustion characteristics, and superior economics, CNG has emerged as an attractive fuel for light-duty and heavy-duty engines. Advanced injection timings, use of oxygenated pilot fuels, EGR, piston bowl geometry optimization, and injector nozzles optimization are the strategies that could be adopted in conventional engines for improving their performance and reducing the emissions in dual-fuel mode. HC, CO, and smoke reduction were observed in dual-fuel engines with advanced injection timings. Combustion simulations and modelling of CNG-diesel dual-engine using the G-equation model are also discussed.

Considering the increase in air pollution and depletion of the available fossil fuels there is a need for the implementation of other energy sources for industrial use and automobiles. Hydrogen fuel is considered as the possible solution to act as a new energy source. It is the ideal means for energy storage for automobiles as it leads to zero emissions in case it is used in fuel cells. Unlike electrical vehicles the hydrogen fuel cells offer advantage of fast recharging and at present there are lot of technologies available which can make the hydrogen production easy and economical in future. However, the wide spread of hydrogen is restricted due its storage as the boiling point of hydrogen is 20.4 K at 1 atm. Thus, the storage of hydrogen in liquid form requires higher pressures and cryogenic conditions which consumes external energy. In addition, storing hydrogen in gaseous form is not feasible as it requires higher volumes. Storing hydrogen in the form of metal hydrides requires hydrogen to react with other metals and it can be released whenever required by breaking bond. Thus, metal hydrides have potential to overcome the problems associated with storage and has many advantages such as thermal stability, automobile safety, no fuel losses and long-term storage, etc. However, lower gravimetric storage density is a major issue beside it requires external source for hydrogen release. According to present automobile manufacturing requirement, the ultimate hydrogen storage material should have high gravimetric reversibility preferably greater than 10wt % of hydrogen, high reversibility which should be greater than 1500 cycles. Many metal hydrides with the suitable catalyst or nanoparticles have shown tendency towards satisfying the above conditions. In the present study, thermodynamic and kinetics for every such metal hydride are mathematically analyzed using the equations based on pore size and surface area. By knowing the thermodynamic and kinetic requirements of metal hydride reactions the suitable material for the automobile can be predicted and the technologies required for the proper release of the hydrogen can be suggested.

Increasing fuel prices and stringent emission regulations are forcing improvements in the performance and emissions of internal combustion engines (ICEs). There are several ways to enhance engine performance and emissions. Waste heat recovery has emerged as a practical solution in recent times. The Organic Rankine Cycle (ORC) is a promising technology to recover the waste heat from various sources and potentially enhance the overall performance of ICEs. The ORC system converts waste heat energy into useful power either for ICEs, renewable energy (geothermal, solar and biomass), or industrial waste heat energy. The ORC systems range from a few kW to multi-MW plants. After a long evolution, this technology has matured. The economic performance of an ORC is very important for its further development and wider application. Integration of ORC with ICEs is gaining popularity among researchers. However, it isn’t very easy and depends on the physicochemical properties of the working fluid (WF) and the heat source temperature. Several optimization methods could improve its performance and decide the optimum operating conditions for the ORC systems.