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Technical Paper

Effect of Hydrogen Enrichment on Flame Morphology and Combustion Evolution in a SI Engine Under Lean Burn Conditions

Uncertainty of fuel supply in the energy sector and environmental protection concerns have motivated studies on clean and renewable alternative fuels for vehicles as well as stationary applications. Among all fuel candidates, hydrogen is generally believed to be a promising alternative, with significant potential for a wide range of operating conditions. In this study, a comparison was carried out between CH4, two CH4/H2 blends and two mixtures of CO and H2, the last one taken as a reference composition representative of syngas. It is imperative to fully understand and characterize how these fuels behave in various conditions. In particular, a deep knowledge of how hydrogen concentrations affect the combustion process is necessary, given that it represents a fundamental issue for the optimization of internal combustion engines. To this aim, flame morphology and combustion stability were studied in a SI engine under lean burn conditions.
Technical Paper

Influence of Water Injection on Performance and Emissions of a Direct-Injection Hydrogen Research Engine

The application of hydrogen (H2) as an internal combustion (IC) engine fuel has been under investigation for several decades. The favorable physical properties of hydrogen make it an excellent alternative fuel for IC engines and hence it is widely regarded as the energy carrier of the future. Direct injection of hydrogen allows optimizing this potential as it provides multiple degrees of freedom to influence the in-cylinder combustion processes and consequently engine efficiency and exhaust emissions. At certain operating conditions the stratification associated with hydrogen direct injection (DI) leads to an efficiency improvement. However, it also results in higher emissions levels. This paper examines the effects of combining an advanced direct injection strategy with water injection for efficiency benefits and emissions reduction of a hydrogen fuelled DI spark ignition (SI) engine.
Technical Paper

Evaluation of Injector Location and Nozzle Design in a Direct-Injection Hydrogen Research Engine

The favorable physical properties of hydrogen (H2) make it an excellent alternative fuel for internal combustion (IC) engines and hence it is widely regarded as the energy carrier of the future. Hydrogen direct injection provides multiple degrees of freedom for engine optimization and influencing the in-cylinder combustion processes. This paper compares the results in the mixture formation and combustion behavior of a hydrogen direct-injected single-cylinder research engine using two different injector locations as well as various injector nozzle designs. For this study the research engine was equipped with a specially designed cylinder head that allows accommodating a hydrogen injector in a side location between the intake valves as well as in the center location adjacent to the spark plug.
Technical Paper

Effect of Natural Gas/Hydrogen Blends on Spark Ignition Stoichiometric Engine Efficiency

Hydrogen (H₂) added to natural gas (NG), improves the combustion process of the air-fuel mixture. This gives the potentiality to develop engines with better performance and lower environmental impact. In any case how hydrogen is produced represents a crucial aspect. In general, if H₂ is produced utilizing fossil fuels and not renewable or nuclear sources, the environmental benefit of CO₂ reduction could be reduced. In this paper two engines, a light-duty (LD) and a heavy-duty (HD), were tested in stoichiometric conditions. The engines were fuelled with NG and with two blends of NG with a 20% and a 40% by volume of H₂, respectively named NG/H₂ 20% and NG/H₂ 40%. The light-duty engine was tested at different loads and speeds, with spark advance set by the electronic control unit (ECU). The ECU actuated a retarded ignition, especially at low load. With the heavy-duty engine, the tests were carried out only at high load.
Technical Paper

Evaluating the Burning Velocity of Gaseous Fuels for Engine Applications: the DHARMA Project

Characterization of combustion parameters of gaseous fuels is the main objective of a novel experimental laboratory, which recently became operational at Istituto Motori: the "Device for Hydrogen-Air Reaction Mode Analysis" (DHARMA in brief) project is meant to generate a systematic database on the burning properties of CH₄, H₂ and other species of interest, in conditions typical of i.c. engines. The experimental setup is based upon an optically accessible cylindrical bomb, where tests are carried out on spherical expanding flames. High-speed shadowgraph is used to record the flame growth and to infer laminar burning parameters. Thorough details are given of the experimental apparatus and the data analysis. Experimental data are presented for the combustion in air of CH₄ and of CH₄/H₂ mixtures: the percentage of hydrogen was 20% and 30% (vol.).
Technical Paper

Simultaneous Shadowgraph/Mie Scattering Imaging of Liquid and Vapor Phases of Diesel Sprays and Validation of a Numerical Model

Diesel sprays from an axially-disposed single-hole injector are studied under both non-vaporizing and vaporizing conditions in a constant-volume vessel. A hybrid shadowgraph/Mie-scattering imaging set-up is used to acquire the liquid and vapor phases of the fuel distribution in a near-simultaneous visualization mode by a high-speed camera (40,000 fps). A diesel injector with k0 factor is used, having the exit-hole diameter of 0.1 mm and the ratio L/d =10. The studies are performed at the injection pressures of 70, 120, and 180 MPa, 25.37 kg/m3 ambient gas density, at the environment temperature of 373, 453 and 900 K. The instantaneous tip penetration of the liquid and vapor phases is extracted from the collected images and processed by a properly assessed software, under the various operating conditions. The AVL FIRE™ code is also used to simulate the spray dynamics. The model is validated on the ground of the collected experimental data.
Technical Paper

Correlation between Simulated Volume Fraction Burned Using a Quasi-Dimensional Model and Flame Area Measured in an Optically Accessible SI Engine

Multi-fuel operation is one of the main topics of investigative research in the field of internal combustion engines. Spark ignition (SI) power units are relatively easily adaptable to alternative liquid-as well as gaseous-fuels, with mixture preparation being the main modification required. Numerical simulations are used on an ever wider scale in engine research in order to reduce costs associated with experimental investigations. In this sense, quasi-dimensional models provide acceptable accuracy with reduced computational efforts. Within this context, the present study puts under scrutiny the assumption of spherical flame propagation and how calibration of a two-zone combustion simulation is affected when changing fuel type. A quasi-dimensional model was calibrated based on measured in-cylinder pressure, and numerical results related to the two-zone volumes were compared to recorded flame imaging.
Technical Paper

Influence of Combustion Efficiency on the Operation of Spark Ignition Engines Fueled with Methane and Hydrogen Investigated in a Quasi-Dimensional Simulation Framework

Within the context of widening application of numerical simulations for shortening engine development times, the present work covers the issue of quasi-dimensional simulation of spark ignition engines. Multi-fuel operation was the main goal of the study, with the analysis of methane and its blends with hydrogen; gasoline was also considered as a reference case. Data recorded on two engines with practically the same geometry, was used for calibrating the model. The first power unit was of commercial derivation for small applications, while the second one featured optical accessibility through the piston crown. The relative difference between the two engines allowed the top-land region crevice to be identified as the major contributor to overall combustion evolution, especially during its late stages.
Journal Article

Characterization of CH4 and CH4/H2 Mixtures Combustion in a Small Displacement Optical Engine

In the last years, even more attention was paid to the alternative fuels which can allow both reducing the fuel consumption and the pollutant emissions. Among gaseous fuels, methane is considered one of the most interesting in terms of engine application. It represents an immediate advantage over other hydrocarbon fuels leading to lower CO₂ emissions; if compared to gasoline, CH₄ has wider flammable limits and better anti-knock properties, but lower flame speed. The addition of H₂ to CH₄ can improve the already good qualities of methane and compensate its weak points. In this paper a comparison was carried out between CH₄ and different CH₄/H₂ mixtures. The measurements were carried out in an optically accessible small single-cylinder, Port Fuel Injection spark ignition (PFI SI), four-stroke engine. It was equipped with the cylinder head of a commercial 250 cc motorcycle engine representative of the most popular two-wheel vehicles in Europe.
Journal Article

Assessment of Multiple Injection Strategies in a Direct-Injection Hydrogen Research Engine

Hydrogen is widely considered a promising fuel for future transportation applications for both, internal combustion engines and fuel cells. Due to their advanced stage of development and immediate availability hydrogen combustion engines could act as a bridging technology towards a wide-spread hydrogen infrastructure. Although fuel cell vehicles are expected to surpass hydrogen combustion engine vehicles in terms of efficiency, the difference in efficiency might not be as significant as widely anticipated [1]. Hydrogen combustion engines have been shown capable of achieving efficiencies of up to 45 % [2]. One of the remaining challenges is the reduction of nitric oxide emissions while achieving peak engine efficiencies. This paper summarizes research work performed on a single-cylinder hydrogen direct injection engine at Argonne National Laboratory.
Journal Article

Study of Basic Injection Configurations using a Direct-Injection Hydrogen Research Engine

The application of hydrogen (H2) as an internal combustion (IC) engine fuel has been under investigation for several decades. The favorable physical properties of hydrogen make it an excellent alternative fuel for fuel cells as well as IC engines and hence it is widely regarded as the energy carrier of the future. The potential of hydrogen as an IC engine fuel can be optimized by direct injection (DI) as it provides multiple degrees of freedom to influence the in-cylinder combustion processes and consequently the engine efficiency and exhaust emissions. This paper studies a single-hole nozzle and examines the effects of injection strategy on engine efficiency, combustion behavior and NOx emissions. The experiments for this study are done on a 0.5 liter single-cylinder research engine which is specifically designed for combustion studies and equipped with a cylinder head that allows side as well as central injector location.