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About this book

This book covers the various advanced reciprocating combustion engine technologies that utilize natural gas and alternative fuels for transportation and power generation applications. It is divided into three major sections consisting of both fundamental and applied technologies to identify (but not limited to) clean, high-efficiency opportunities with natural gas fueling that have been developed through experimental protocols, numerical and high-performance computational simulations, and zero-dimensional, multizone combustion simulations. Particular emphasis is placed on statutes to monitor fine particulate emissions from tailpipe of engines operating on natural gas and alternative fuels.

Table of Contents

Frontmatter

Chapter 1. Introduction to Advanced Combustion Technologies: The Role of Natural Gas in Future Transportation and Power Generation Systems

Abstract
Among the many alternatives to gasoline and diesel, natural gas is considered a viable fuel for future transportation and power generation applications. The present chapter provides an introductory overview of the role of natural gas in future transportation and power generation systems. Current and projected trends (up to 2040) for global energy consumption and the associated contribution of natural gas in various sectors (industrial, transportation, residential, etc.) are discussed. The advantages and challenges of natural gas as a combustion fuel, natural gas fuel storage and transportation challenges (as compressed natural gas and liquefied natural gas), and natural gas utilization in internal combustion (IC) engines are reviewed. Advanced natural gas low-temperature combustion (LTC) strategies for IC engines, natural gas combustion in spark ignition (SI) engines with a specific focus on direct injection of natural gas, natural gas utilization in marine SI and compression ignition (CI) engines, natural gas utilization in light-duty, heavy-duty, industrial, and marine engines, emissions control technologies for natural gas-fueled engines, and a review of natural gas-powered residential scale micro-combined heating and power (CHP) systems are the major topics explored in the book. The organizational rationale of the book is discussed, and brief summaries of various chapters in the book are provided.
Kalyan Kumar Srinivasan, Avinash Kumar Agarwal, Sundar Rajan Krishnan, Vincenzo Mulone

Chapter 2. Low-Temperature Natural Gas Combustion Engines

Abstract
Advanced or low-temperature combustion engines have shown the potential to achieve high fuel conversion efficiency with minimal emissions formation and therefore can provide solutions for future powertrain systems. Numerous advanced combustion concepts have been explored, including both spark-ignited and compression-ignited concepts, and each one has been investigated using different liquid or gaseous fuels. This chapter will discuss the potential of using natural gas as a fuel for future advanced combustion engines and will present the associated benefits and challenges. The low carbon-to-hydrogen atom ratio of natural gas can enable a highly efficient combustion process with low CO2 formation; its chemical composition mitigates soot formation during combustion, and its high octane number enables high compression ratio operation of spark-ignited engines with good knock resistance. However, the low reactivity of natural gas inhibits the compression ignition of lean fuel–air mixtures, and any combustion inefficiency may result in direct methane emissions in the exhaust. These characteristics have led researchers to investigate lean natural gas combustion using prechambers (jet ignition), high-pressure direct injection (HPDI) of diesel and natural gas mixtures, micro-pilot injection concepts with premixed natural gas and direct-injected diesel fuel, as well as kinetically controlled and low-temperature combustion concepts such as Homogeneous Charge Compression Ignition (HCCI) and Reactivity Controlled Compression Ignition (RCCI) combustion. This chapter will discuss the use of natural gas in the HCCI and RCCI combustion concepts and analyze the associated benefits and challenges.
Sotirios Mamalis

Chapter 3. The Ultra-Lean Partially Stratified Charge Approach to Reducing Emissions in Natural Gas Spark-Ignited Engines

Abstract
Lean-burn natural gas engines can be used to reduce exhaust emissions significantly. However, as the mixture is leaned out, the occurrence of extinction and incomplete combustion increases, resulting in poor performance and stability, as well as elevated levels of unburned hydrocarbon (UHC) and nitrogen oxides (NOx) emissions. The partially stratified charge (PSC) method can be used to mitigate these issues, while extending the lean misfire limit (LML) beyond its equivalent, homogeneous level. In this chapter, the PSC ignition and combustion processes are examined following a comprehensive experimental and numerical approach. Experiments are conducted in an idealized PSC configuration, using a constant volume combustion chamber (CVCC), to identify the principle enabling mechanisms of the PSC methodology. Engine tests conducted in a single-cylinder research engine (SCRE) demonstrate the feasibility of various PSC implementations in improving performance and emission characteristics in real-world settings. Complementary numerical analyses for the CVCC are obtained through large eddy simulations (LES), while Reynolds-averaged Navier–Stokes (RANS) simulations are conducted for SCRE with reduced chemical kinetics. The corresponding simulated results provide additional insights in characterizing the effect of fuel stratification on flame kernel maturation and flame propagation, the interplay between chemistry and turbulence at different overall air–fuel ratios, as well as formation of major pollutant species.
L. Bartolucci, E. C. Chan, S. Cordiner, R. L. Evans, V. Mulone

Chapter 4. Simulation and Modeling of Direct Gas Injection through Poppet-type Outwardly-opening Injectors in Internal Combustion Engines

Abstract
The obligation for the development of highly efficient and low-emission combustion engines has renewed interest in compressed natural gas (CNG) engines using a direct injection (DI) system. CNG has high knock resistance, and with the use of DI, the volumetric efficiency can be increased compared to port-injected CNG engines. Additionally, carbon dioxide and particulate emissions are lower due to a high hydrogen-to-carbon ratio. Therefore, the DI-CNG technology has the potential to surpass the thermal efficiency of conventional gasoline spark-ignition engines while producing lower emissions. However, the design of DI-CNG engines is challenging because of gaseous and, hence, highly compressible fuel running through small injector passages, which results in complex supersonic flows with shocks. The supersonic gas jets emerging from the injector outlet interact with the in-cylinder flow field, which has an impact on fuel–air mixing and combustion. Therefore, it is essential to understand the fundamental physics of the injection process to develop modeling strategies for DI-CNG systems and further study the influence of direct gas injection on the in-cylinder flow field and mixing. To this end, the current chapter is dedicated to the fundamental understanding of the gas injection process through poppet-type outwardly-opening injectors. The DI modeling strategies are discussed for the application in engine simulations. Furthermore, the impact of gas injection on the in-cylinder flow field and fuel–air mixing is analyzed for centrally-mounted injector configurations.
Abhishek Y. Deshmukh, Mathis Bode, Tobias Falkenstein, Maziar Khosravi, David van Bebber, Michael Klaas, Wolfgang Schröder, Heinz Pitsch

Chapter 5. Prospects and Challenges for Deploying Direct Injection Technology for Compressed Natural Gas Engines

Abstract
In this chapter, prospects and challenges of direct injection (DI) compressed natural gas (CNG) engine technology are dealt with and compared with conventional port fuel injection (PFI) technology used for CNG induction. DI injector nozzle geometries are discussed along with their performance using optical diagnostics tools such as Schlieren imaging and planar laser-induced fluorescence (PLIF) technique. Different CNG induction methodologies are compared along with different fueling arrangements such as induction of 100% natural gas (NG), bi-fuel, and dual-fuel systems. DI and PFI engines are compared for volumetric efficiency for varying fuel injection timings. In a single-cylinder prototype engine, engine parameters are analyzed for a different start of injection (SOI) timings with varying brake mean effective pressure (BMEP) and equivalence ratio (Φ). Advanced SOI reduced the brake-specific fuel consumption (BSFC), increased the brake thermal efficiency (BTE), and reduced the emissions.
Rajesh Kumar Prasad, Tanmay Kar, Avinash Kumar Agarwal

Chapter 6. Effects of EGR on Engines Fueled with Natural Gas and Natural Gas/Hydrogen Blends

Abstract
The exhaust gas recirculation can be used in a stoichiometric engine, for suppressing knocking and increasing efficiency, without a significant impact on pollutant emissions, since charge dilution is obtained with inert gases, allowing closed-loop control operations. However, relatively high EGR rates make worse the combustion process. This chapter deepens the effects of EGR on the performance of gaseous powered engines. In particular, the experimental data have been obtained fueling two engines with NG and NG/H2 mixtures until 40% by volume of hydrogen, at steady state for different loads, measuring emissions upstream and downstream the three-way catalyst and analyzing the combustion process. A naturally aspirated light-duty spark ignition engine and a turbocharged heavy-duty one were tested. The results obtained with the two engines were consistent with each other. In particular, EGR could be utilized to have high specific power, with reduced thermal stress, but also to increase engine efficiency. Moreover, NG fueling permits a large flexibility in EGR system design, due to very clean engine-out exhaust gas, without visible particles. H2 added to NG allows to mitigate the effect of EGR in reducing combustion speed. The positive effect of H2 as combustion booster is more evident at EGR rate increasing. Nevertheless, with EGR, an increment of raw THC emission has been observed. Moreover, for the lower exhaust gas temperatures, oxidation of THC in the catalyst could result less effective. For these reasons, the blends with high hydrogen content, allowing a significant reduction of THC formation directly in the combustion chamber, can be usefully utilized for engines optimization with high EGR rates.
Luigi De Simio, Michele Gambino, Sabato Iannaccone

Chapter 7. Natural Gas Combustion in Marine Engines: An Operational, Environmental, and Economic Assessment

Abstract
The present study contains a detailed assessment of the state-of-the-art technologies of two-stroke (2-S) and four-stroke (4-S) dual-fuel compression-ignition (CI) engines and four-stroke spark-ignited (SI) natural gas engines from technological, operational, environmental, and economic standpoints. Emphasis will be given to the examination of the effect of natural gas combustion on the performance characteristics and pollutant emissions of marine two-stroke dual-fuel engines and four-stroke dual-fuel and gas SI engines. Also, the CO2 and CH4 using EEDI analysis are examined for LNG carriers equipped with three different propulsion systems. The final outcome of the proposed study will be the definition of the parameters that should be taken into account to identify the optimum two-stroke and four-stroke natural gas engine technology frame, which can be used in the near future, as either main propulsion (two-stroke or four-stroke) or auxiliary (four-stroke) engines in marine applications.
Roussos G. Papagiannakis, Theodoros C. Zannis, Efthimios G. Pariotis, John S. Katsanis

Chapter 8. Advanced Combustion in Natural Gas-Fueled Engines

Abstract
Current energy and emission regulations set the requirements to increase the use of natural gas in engines for transportation and power generation. The characteristics of natural gas are high octane number, less amount of carbon in the molecule, suitable to lean combustion, less ignitibility, etc. There are some advantages of using natural gas for engine combustion. First, less carbon dioxide is emitted due to its molecular characteristics. Second, higher thermal efficiency is achieved owing to the high compression ratio compared to that of gasoline engines. Natural gas has higher octane number so that knock is hard to occur even at high compression ratios. However, this becomes a disadvantage in homogeneous charge compression ignition (HCCI) engines or compression ignition engines because the initial auto-ignition is difficult to be achieved. When natural gas is used in a diesel engine, primary natural gas–air mixture is ignited with small amount of diesel fuel. It was found that under high pressure, lean conditions, and with the control of certain parameters, the end gas is auto-ignited without knock and improves the engine combustion efficiency. Recently, some new fuel ignition technologies have been developed to be applied to natural gas engines. These are the laser-assisted and plasma-assisted ignition systems with high energy and compact size.
Ulugbek Azimov, Nobuyuki Kawahara, Kazuya Tsuboi, Eiji Tomita

Chapter 9. Advances of the Natural Gas/Diesel RCCI Concept Application for Light-Duty Engines: Comprehensive Analysis of the Influence of the Design and Calibration Parameters on Performance and Emissions

Abstract
The increasing energy demand together with the severe emission legislation of the transportation sector requires effective solutions for automotive propulsion systems. The transportation sector is responsible for 23% of the total CO2 in the European Union. Advanced combustion concepts combined with alternative fuels, if properly tuned, have the potential to increase the efficiencies and lower emissions, compared to the conventional diesel or spark-ignition combustion. This is particularly valid when natural gas (a low reactivity fuel with low auto-ignition characteristics) and fossil diesel (the high reactivity one with high auto-ignition characteristics) are fuelled together in a compression ignition engine approaching the reactivity controlled compression ignition (RCCI) combustion. However, the use of these fuels in an advanced compression ignition engine increases the degrees of freedom for the tuning of the whole system. In order to carry out robust calibrations for efficiency maximization and pollutant minimization, in the whole engine-operating area, a detailed sensitivity analysis to the functional parameters versus fuel consumption and pollutant emissions is a paramount. Based on the experiences carried out at the laboratory of Istituto Motori of CNR, the chapter analyses the correlation between the main design and operating parameters versus the engine performance, providing a scale of degree of influence of the selected parameters as useful information for the engine calibration engineers.
Giacomo Belgiorno, Gabriele Di Blasio, Carlo Beatrice

Chapter 10. Design and Calibration Strategies for Improving HCCI Combustion in Dual-Fuel Diesel–Methane Engines

Abstract
The interest in methane is lately increased due to power-to-gas technologies, through which green electricity in excess could be used to produce easily storable gaseous fuels. Among engines for methane exploitation, dual-fuel piston engine is a very efficient and low-impact solution. Their operation, still limited by high hydrocarbons and carbon monoxide emissions at low loads and knock at high loads, is characterized by many parameters. Besides the ones well recognized in the literature, like pilot quantity and substitution rate, other parameters, like engine volumetric compression ratio, intake charge conditions, pilot injection pressure and timing, engine load and speed, and exhaust gas recirculation (EGR), showed an impact on engine performance and emissions. This work first describes the results of a full factorial DoE in which the effects of compression ratio, intake charge pressure (ICP), pilot injection timing and pressure, and methane flow rate effect are evaluated and discussed on combustion development, engine performance, and pollutant emission levels at the exhaust. Through analysis of variance (ANOVA), the first- and second-order effects were also quantified. Moreover, the factor variation ranges leading the engine to operate in or close to HCCI combustion, i.e., guaranteeing a high conversion efficiency and low emission levels at the same time, were sought and highlighted. This suggested that not only very advanced but also retarded injection timings, combined with high ICP, determine very low levels of nitrogen oxides and maximum pressure rise rate, with little or no penalty on engine efficiency and emission levels.
A. P. Carlucci, A. Ficarella, D. Laforgia, L. Strafella

Chapter 11. Dual Fuel (Natural Gas Diesel) for Light-Duty Industrial Engines: A Numerical and Experimental Investigation

Abstract
This paper reviews the main results of a numerical and experimental activity, carried out on an automotive four-cylinder, common rail, 2.8 L turbocharged diesel engine, Euro IV compliant. The purpose of the project is to convert this engine, with minor hardware modifications, in order to operate in compression ignition (CI) dual-fuel (DF) mode, using natural gas (NG) as the main source of energy. The diesel injector will keep the only function to ignite the homogeneous air–NG mixture within the cylinder, injecting just a small quantity of diesel fuel. In this way, soot emissions can be almost completely eliminated, and the after-treatment system can be strongly simplified (then, its cost reduced). Other fundamental advantages in the use of NG instead of diesel are the lower emission of CO2 (provided that brake efficiency is not reduced when running on DF) and the lower concentration of nitrogen oxides (NOx). This DF engine would be particularly suitable for light-duty industrial applications (power generators, small tractors, and off-road vehicles) and boats, where the installation of an additional fuel system is not limited by tight constraints. The experimental activity is supported by a comprehensive theoretical study, carried out through CFD simulation (both 1D and 3D). The numerical models are first calibrated for the standard combustion mode and then applied to get the guidelines for the development and calibration of the physical prototype. The most relevant experimental result is obtained at 3000 rpm, BMEP = 12 bar, where the DF engine can work with just a 20% of the diesel fuel required for standard operations. The following advantages are found: (1) complete elimination of soot; (2) 26% reduction of NOx; (3) 25% reduction of CO2; (4) slight improvement of brake efficiency. The only downside is the strong increase in HC and CO concentrations, which are about ten times higher. However, this issue can be addressed installing a cost-effective oxidation catalyst.
Enrico Mattarelli, Carlo Alberto Rinaldini, Tommaso Savioli

Chapter 12. Cyclic Combustion Variations in Diesel–Natural Gas Dual Fuel Engines

Abstract
Dual fuel combustion is achieved by using a combination of two fuels with extremely different ignition characteristics. For instance, a low-reactivity fuel such as natural gas is compression-ignited using a calibrated amount of appropriately timed, high-pressure, high-reactivity diesel spray. The ensuing combustion occurs at predominantly fuel-lean conditions and is therefore devoid of soot emissions, and the relatively small amount of diesel fuel used also results in the simultaneous reduction in nitrogen oxide emissions. In addition, the use of natural gas, which is predominantly composed of methane, offers the necessary fuel flexibility required to reduce carbon dioxide emissions from conventional neat diesel fired power trains in transportation and power generation applications. The greatest reductions in carbon dioxide emissions are achieved with highest natural gas substitution. However, this also causes problems with high cyclic combustion variations leading to an increased propensity to misfire and high engine-out hydrocarbon emissions. This chapter reviews the current state of the art in strategies to mitigate cyclic combustion variations in dual fuel natural gas engines and provides substantial insights gleaned from past experimental dual fuel combustion research conducted by the authors. In particular, the chapter discusses opportunities and challenges associated with low-temperature dual fuel combustion engines.
Kalyan Kumar Srinivasan, Sundar Rajan Krishnan, Prabhat Ranjan Jha, Hamidreza Mahabadipour

Chapter 13. Emissions Control Technologies for Natural Gas Engines

Abstract
In recent years, there has been a rising interest in alternative cleaner low-carbon fuels as they have a significant potential in decreasing the harmful exhaust emissions and contribute in decarbonising transportation. Natural gas (NG) is one of the most promising alternative fossil fuel that has been widely investigated in internal combustion (IC) engines. It is expected that global consumption of NG from 2015 to 2040 will rise 1.4% annually, accounting for the largest increase in world primary energy consumption. In this chapter, a review of the performance of NG-fuelled internal combustion engines, exhaust emissions produced from the combustion of natural gas engines and aftertreatment systems used to control those emissions is performed. In addition to the reduction of carbon dioxide (CO2) from NG fuelling, lower levels of unburnt hydrocarbons (HC) and particulate matter emissions (PM) than conventional petrol and diesel engines have also been reported. However, they tend to produce higher nitrogen oxide (NOx) and methane (CH4) emissions which are difficult to oxidise, particularly at engine operation at stoichiometric conditions. On the other hand, the slow flame speed of NG is a major problem under lean-burn operation as it increases cycle-to-cycle variations, significantly compromising engine efficiency. The addition of hydrogen enhances the combustion of NG in addition to improving engine stability and reducing exhaust emissions. The difference in combustion, emission characteristics and aftertreatment systems of stoichiometric, lean-burn and hydrogen-enriched natural gas engines is outlined.
A. Wahbi, A. Tsolakis, J. Herreros

Chapter 14. A Review of Residential-Scale Natural Gas-Powered Micro-Combined Heat and Power Engine Systems

Abstract
A combined heat and power (CHP) system typically employs a prime mover generator that produces electricity on-site and utilizes waste heat energy to supplement a site’s thermal load requirements. Micro-CHP, notionally defined as CHP systems with a capacity lower than 50 kW, offers an alternative, and in some cases a complementary, solution to centralized power generation. A micro-CHP system would be typically installed at a residential or small commercial site where it would consume fuel such as diesel or natural gas to generate electricity locally and further use the rejected waste heat for local heating, air-conditioning, and/or humidification needs. This is in contrast to the rejected heat being dissipated at centralized power plants using cooling towers. The combined efficiency of primary energy usage for such systems can be higher than 90% on a fuel lower heating value (LHV) basis. Since a large fraction of the electricity generated from all the centralized power plants is consumed by the residential and commercial sectors, CHP implementation in these sectors can have a huge impact on both energy savings and carbon dioxide (CO2) emissions’ reduction. Apart from these benefits, decentralized CHP as a form of distributed electricity generation offers numerous advantages such as reduced electrical grid stress, reduced electricity transmission and distribution losses, and potentially improved resiliency of the electricity grid. Various technologies including reciprocating internal combustion engines, Stirling engines, Brayton cycle engines, Rankine cycle engines, fuel cells, and solid-state devices such as thermoelectric generators and thermionic generators can be used as micro-CHP systems. This chapter provides a detailed technological review of engine-based micro-CHP systems and further presents the challenges and opportunities for achieving high fuel conversion efficiency.
Gokul Vishwanathan, Julian Sculley, David Tew, Ji-Cheng Zhao
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