Small Amount Of Hydrogen Addition Research Articles

Study on SI Engine Operation Stability at Lean Condition—The Effect of a Small Amount of Hydrogen Addition

The lean-burn mode is a solution that reduces the fuel consumption of spark-ignition internal combustion engines and keeps the low exhaust emission, but the stability of the lean-burn combustion process, especially at low loads, needs to be addressed. Enhancing gasoline with hybrid hydrogen oxygen (HHO) gas—a mixture of hydrogen and oxygen gases—is proposed to improve combustion of the lean-gasoline mixture. A three-cylinder, spark-ignition, naturally aspirated, MPI engine with HHO gas produced with an alkaline water electrolyzer and introduced as a gasoline enhancement was tested. The amount of hydrogen added to the lean-gasoline mixture (λ = 1.4) was in the range from 0.15 to 1.5%, and the results were compared to the stoichiometric (λ = 1) and pure lean mode (λ = 1.4) gasoline operation. The other authors’ results show that a minimum 3% of the mass fraction of hydrogen is necessary to affect the gasoline combustion process. This paper proved that even a small hydrogen enhancement of gasoline in the amount of 0.3% of the mass fraction improves the combustion stability.

Hydrogen production from ammonia-rich combustion for fuel reforming under high temperature and high pressure conditions

Ammonia is a promising carbon-free fuel for internal combustion engines. However, the low reactivity and combustion sluggishness make ammonia difficult to be used in a single-fuel way. A small amount of hydrogen addition has been demonstrated beneficial to improving ammonia’s reactivity and engine performance. To overcome the safety and cost issues of onboard hydrogen storage on vehicles, we propose to produce hydrogen by in-cylinder ammonia reforming through ammonia-rich combustion. This paper presents an investigation on the hydrogen production from ammonia-rich combustion on a rapid compression machine (RCM) over conditions with varying pressures (22–36 bar), temperatures (1200–1300 K), and equivalence ratios (1.75–2.25). Both major combustion reactants (NH3) and products (H2 and N2) were analyzed using a fast sampling system and gas chromatography (GC). Chemical analysis was also conducted to interpret the experimental results. The results showed that current ammonia mechanisms were inadequate to predict the ignition delay time and the hydrogen production trend under engine-relevant and fuel-rich conditions. The experimental hydrogen production increased with the increasing initial temperature, which could be ascribed to the increase in reaction rate constants of key reactions. For the effect of pressure, the hydrogen production was found to first increase and then decrease as the initial pressure increased, which failed to be predicted by simulations. In the tested equivalence ratio range, a moderate fuel-rich equivalence ratio of two produced the highest hydrogen, in which the combined impact of key radical pool buildup (NH3 and NH2) and the change in reaction ratios of key reactions (NH2 + H->NH + H2) was responsible.

Experimental study of kerosene supersonic combustion with pilot hydrogen and fuel additive under low flight mach conditions

Reliable ignition and efficient combustion are critical for low flight Mach starting stage of dual-mode scramjet. In this paper, liquid kerosene ignition and combustion with pilot hydrogen and fuel additive were experimentally studied in a model supersonic combustor with clean air inflow, under the simulated conditions of flight Mach 3.8–4.0. The selected composite additive is mainly composed of about 20%-vol low-carbon small-molecular unsaturated alkanes and about 80%-vol diethylmethoxyborane. It is found that, under the low-temperature supersonic conditions, either RP-3 kerosene or with additives can all be ignited by the pilot hydrogen flame of least ERH = 0.065–0.076, only fuel additive effects seem to be still not enough for auto-ignition. Self-sustaining flame stabilization and combustion were realized with the tandem dual-cavity flame-holders, an appropriate amount of hydrogen addition can significantly promote the liquid kerosene combustion heat release without inlet disturbing. Enhancement of kerosene supersonic combustion and faster/higher temperature rises with the fuel additive of certain concentration were experimentally validated, and the positive effects showed more significant at a lower equivalence ratio of ERK = 0.43, in which the combustion enhancement induced mode transition from transonic to subsonic is found due to the 20%-vol additive. The additive effects might be greatly depended on the concentration in a nonlinear way when reducing concentration from 20%-vol to 10%-vol, a small concentration of 10%-vol additive did not produce an obvious enhancement effect. A small amount of hydrogen addition or an appropriate proportion of additive can improve the combustor performance, while too high total equivalence ratios or large amount of hydrogen addition tend to lower combustion efficiency.

Investigation of kerosene supersonic combustion performance with hydrogen addition and fuel additive at low Mach inflow conditions

Stable and efficient combustion is critical for low Mach starting stage of Dual-Mode Scramjet. In this paper, basic experimental validation and three-dimensional simulation of hydrogen addition and fuel additive effects on kerosene supersonic combustion performance were conducted under flight Mach 3.8 inflow conditions. Hydrogen addition was injected independently and the additive effects were simulated by the method of reducing activation energy. The simulation results are well-agreed with the experimental measurements from hydrogen addition cases and 20%-vol additive cases, validating the numerical method and models employed. The relative activation energy needed for well simulating 20%-vol additive effects tends to be higher than the theoretical prediction and also different by equivalence ratios. The heat release is intensified by either hydrogen addition or fuel additive, resulting in higher temperature-rises and pressure-rises, and more OH radicals for combustion enhancements at low-temperature conditions. An appropriate small amount of hydrogen addition (ERH < 0.08) can promote kerosene pre-evaporation and combustion heat release to achieve higher combustion efficiency; a large amount of hydrogen addition exhibits a competitive mechanism with kerosene cracking and CO oxidation conversion, also reduces the degree of diffusive mixing. Either the same small amount of hydrogen addition or fuel additive, more significant enhancement effects can be observed at the lower equivalence ratio of kerosene, due to the increased heat release induced flame stabilization and combustion mode transition. Compared with hydrogen addition, combustion efficiencies with increasing additive effects are increased monotonously to a higher level when kerosene equivalence ratio of ERK = 0.53, whereas lower efficiencies when ERK = 0.43.

Thermodynamic modeling and parametric study of a small-scale natural gas/hydrogen-fueled gas turbine system for decentralized applications

In this study a detailed thermodynamic model of a small-scale natural gas/hydrogen-fueled gas turbine system is presented. The thermodynamic model includes both a basic thermodynamic analysis and an exergy analysis. Exergy analysis aims on the identification of exergy destruction in the various system components. Specifically, it is investigated how hydrogen addition in the fuel supply can affect exergy loss. Off-design modeling is also implemented to realistically evaluate performance at part-load operation. A parametric study is conducted to examine the effect of hydrogen ratio on system performance. The hydrogen ratio is varied from 0 to 0.9, to examine the behavior of the developed model at different hydrogen contents. The results suggest that hydrogen addition to the natural gas fuel supply can change the operational behavior of the gas turbine cycle. Although net electrical efficiency is only marginally increased as hydrogen ratio is increased (0.347 vs. 0.356), the exergetic efficiency is more significantly affected, mainly due to the reduction of combustor losses as hydrogen content increases (0.338 vs. 0.360). Also, hydrogen addition has a positive effect in terms of carbon emissions, since even a tiny hydrogen injection at a hydrogen ratio of 0.1 (on a volumetric basis) results in a 6.1% reduction in CO2 emissions, as compared to methane-only fueling. Overall, the results suggest that even a small amount of hydrogen addition to the gas turbine cycle can have a significantly positive effect in terms of system efficiency and operational cost.

Effect of hydrogen addition on the combustion and emission of a diesel free-piston engine

The free-piston engine (FPE) is a new crankless engine, which operates with variable compression ratio, flexible fuel applicability and low pollution potential. A numerical model which couples with dynamic, combustion and gas exchange was established and verified by experiment to simulate the effects of different hydrogen addition on the combustion and emission of a diesel FPE. Results indicate that a small amount of hydrogen addition has a little effect on the combustion process of the FPE. However, when the ratio of hydrogen addition (RH2) is more than 0.1, the RH2 gives a positive effect on the peak in-cylinder gas pressure, temperature, and nitric oxide emission of the FPE, while soot emission decreases with the increase of hydrogen addition. Moreover, the larger RH2 induces a longer ignition delay, shorter rapid combustion period, weaker post-combustion effect, greater heat release rate, and earlier peak heat release rate for the FPE. Nevertheless, the released heat in rapid combustion period is significantly enhanced by the increase of RH2.

The effects of small amount of hydrogen addition on performance and emissions of a direct injection compression ignition engine

The effects of small amount of hydrogen addition on performance and emissions of a direct injection compression ignition engine

Effect of addition of hydrogen and exhaust gas recirculation on characteristics of hydrogen gasoline engine

The effects of exhaust gas recirculation (EGR) on combustion and emissions under different hydrogen ratios were studied based on an engine with a gasoline intake port injection and hydrogen direct injection. The peak cylinder pressure increases by 9.8% in the presence of a small amount of hydrogen. The heat release from combustion is more concentrated, and the engine torque can increase by 11% with a small amount of hydrogen addition. Nitrogen oxide (NOx) emissions can be reduced by EGR dilution. Hydrogen addition offsets the blocking effect of EGR on combustion partially, therefore, hydrogen addition permits a higher original engine EGR rate, and yields a larger throttle opening, which improves the mechanical efficiency and decreases NOx emissions by 54.8% compared with the original engine. The effects of EGR on carbon monoxide (CO) and hydrocarbon (HC) emissions are not obvious and CO and HC emissions can be reduced sharply with hydrogen addition. CO, HC, and NOx emissions can be controlled at a lower level, engine output torque can be increased, and fuel consumption can be reduced significantly with the co-control of hydrogen addition and EGR in a hydrogen gasoline engine.

Laminar flame propagation and ignition properties of premixed iso-octane/air with hydrogen addition

Numerical simulations of one-dimensional planar and spherical flame propagation of iso-octane/hydrogen/air mixtures at different equivalence ratios and hydrogen blending levels are conducted considering detailed chemistry. Our focus is on the effects of hydrogen addition on laminar flame propagation and ignition of iso-octane/air mixtures. Specifically, the laminar flame speed, Markstein length, and minimum ignition energy of iso-octane/hydrogen binary fuel blends are investigated. The laminar flame speed is found to increase first slightly and then exponentially with the molar ratio of hydrogen in the iso-octane/hydrogen binary fuel blends. However, a nearly linear trend is observed when the mass ratio instead of molar ratio of hydrogen blending is considered. Similar trend holds for hydrogen addition to other hydrocarbon fuels such as methane and propane. The thermal and chemical effects involved in laminar flame speed enhancement by hydrogen addition are quantified and it is found that the chemical effect prevails over the thermal effect. Unlike the laminar flame speed, the Markstein length is found to change non-monotonically with hydrogen blending ratio. Blending hydrogen to iso-octane/air and blending iso-octane to hydrogen/air both promote diffusive-thermal instability. Moreover, the minimum ignition energy of iso-octane/air is shown to be reduced by a small amount of hydrogen addition, especially for the fuel lean case. When the hydrogen blending molar ratio is above 60%, the minimum ignition energy is found to be insensitive to hydrogen addition.

Effects of hydrogen addition on combustion characteristics of n-decane/air mixtures

To explore the possibility of simultaneously extending the lean extinction limit and reducing the emission levels with hydrogen addition, a computational study is performed to investigate the effects of hydrogen addition on the fundamental combustion characteristics of n-decane/air mixtures. It is found that a small amount of hydrogen addition can significantly promote the reactivity of n-decane/air mixtures, leading to shortened ignition delays at high temperatures, increased laminar flame speeds, and reduced extinction residence times. The results on emissions show that the addition of hydrogen leads to a reduction in CO emission index under fuel rich conditions, while NO emission index increases with increasing hydrogen addition for all the conditions examined. The extent of the hydrogen addition effects on different combustion responses at varying pressures has also been investigated. In addition, sensitivity analysis has been conducted to identify the key reactions that are responsible for the enhanced reactivity associated with hydrogen addition. The present results further demonstrate that with the aid of hydrogen addition, leaner and hence cleaner combustion can be achieved without compromising static flame stability.

Measurement and correlation of laminar flame speeds of CO and C 2 hydrocarbons with hydrogen addition at atmospheric and elevated pressures

The laminar flame speeds of mixtures of ethane, ethylene, acetylene, and carbon monoxide with small amount of hydrogen addition at atmospheric and elevated pressures were experimentally and computationally determined. It was found that the approximate linear correlation identified previously between the laminar flame speeds and an appropriate definition of the amount of hydrogen addition for methane, propane and n-butane at atmospheric pressure also largely applies to ethane, ethylene, and acetylene at atmospheric as well as elevated pressures. The linear correlation, however, does not hold for carbon monoxide, at all pressures, due to the strong catalytic effect of hydrogen on the oxidation of carbon monoxide. A mechanistic analysis shows that both the Arrhenius and diffusive contributions to the laminar flame speed are nearly linear functions of the hydrogen addition, which explains this overall approximate linear correlation.

1202 噴霧燃焼における微量水素添加の影響(GS-6 燃焼(1))

1202 噴霧燃焼における微量水素添加の影響(GS-6 燃焼(1))

Characterization of the effects of hydrogen addition in premixed methane/air flames

The use of hydrogenated fuels shows considerable promise for applications in gas turbines and internal combustion engines. In the present work, the effects of hydrogen addition in methane/air flames are investigated using both a laminar flame propagation facility and a high-pressure turbulent flame facility. The aim of this research is to contribute to the characterization of lean methane/hydrogen/air premixed turbulent flames at high pressures, by studying the flame front geometry, the flame surface density and the instantaneous flame front thermal thickness distributions. The experiments and analyses show that a small amount of hydrogen addition in turbulent premixed methane–air flames introduces changes in both instantaneous and average flame characteristics.