Performance and combustion characteristics of a direct injection SI hydrogen engine

Hydrogen with low spark-energy requirement, wide flammability range and high burning velocity is an important candidate for being used as fuel in spark-ignition engines. It also offers CO₂ and HC free combustion and lean operation resulting in lower _NOx${\mathrm{NO}}_x$ emissions. However, well examined external mixing of hydrogen with intake air causes backfire and knock especially at higher engine loads. In addition, low heating value per unit of volume of hydrogen limits the maximum output power. In this study, attention was paid to full usage of hydrogen advantage employing internal mixing method. Hydrogen was directly injected into cylinder of a single-cylinder test engine using a high-pressure gas injector and effects of injection timing and spark timing on engine performance and _NOx${\mathrm{NO}}_x$ emission were investigated under wide engine loads. The results indicate that direct injection of hydrogen prevents backfire, and that high thermal efficiency and output power can be achieved by hydrogen injection during late compression stroke. Moreover, by further optimization of the injection timing for each engine load, _NOx${\mathrm{NO}}_x$ emission can be reduced under the high engine output conditions.     

Analysis of the benefits of carbon credits to hydrogen addition to midsize gas turbine feedstocks

The addition of hydrogen to the natural gas feedstocks of midsize (30–150 MW) gas turbines was analyzed as a method of reducing nitrogen oxides (_NOx)$({\mathrm{NO}}_x)$ and _CO2${\mathrm{CO}}_2$ emissions. In particular, the costs of hydrogen addition were evaluated against the combined costs for other current _NOx${\mathrm{NO}}_x$ and _CO2${\mathrm{CO}}_2$ emissions control technologies for both existing and new systems to determine its benefits and market feasibility. Markets for _NOx${\mathrm{NO}}_x$ emissions credits currently exist in California and the Northeast States and are expected to grow. Although regulations are not currently in place in the United States, several other countries have implemented carbon tax and carbon credit programs. The analysis thus assumes that the United States adopts future legislation similar to these programs. Therefore, potential sale of emissions credits for volunteer retrofits was also included in the study. It was found that hydrogen addition is a competitive alternative to traditional emissions abatement techniques under certain conditions. The existence of carbon credits shifts the system economics in favor of hydrogen addition.     

Hydrogen injection as additional fuel in gas turbine combustor. Evaluation of effects

Industrial gas turbines fuelled by fossil fuels have been used widely in power generation and combined heat and power for many years. However they have to meet severe _NOx${\mathrm{NO}}_x$, CO and _CO2${\mathrm{CO}}_2$ (greenhouse effect) emissions legislation in many countries. This paper reports a study on injection of small quantities of hydrogen in a hydrocarbon fuelled burner like additionally fuel to reduce the pollutants emissions. Hydrogen is injected in the primary zone, premixed with the air. Using this injection together lean primary zone, it is possible to reduce the _NOx${\mathrm{NO}}_x$ level while CO an HC levels remains approximately constant.     

Effects of bluff-body shape on LPG–H2 jet diffusion flame

The effects of bluff-body lip thickness on the several physical parameters like flame length, radiant fraction, gas temperature and _NOx${\mathrm{NO}}_x$ emissions in liquefied petroleum gas (LPG)–H₂ jet diffusion flame are investigated experimentally. Results indicate that the flame length reduces with the addition of hydrogen in the bluff-body stabilized flame, which can be attributed to the enhanced reactivity and residence time of the mixture gases. Moreover, with increasing lip thickness of the bluff body, the flame length also gets reduced. The soot free length fraction (SFLF) is observed to be enhanced with H₂ addition to the fuel stream. In contrast, the SFLF gets reduced with increasing lip thickness repetition, which is due to the reduced induction period of soot formation. The emission index of _NOx${\mathrm{NO}}_x$ (_EINOx${\mathrm{EINO}}_x$) is found to be attenuated in coaxial burner with hydrogen addition. In contrast it is observed to be enhanced in bluff-body stabilized flame. The former is due to the reduction in residence time of gas mixture, whereas the latter can be explained on the basis of increased flame temperature. Besides this, _NOx${\mathrm{NO}}_x$ emission level is also found to be enhanced with increasing lip thickness due to enhanced residence time.     

Intake charge dilution effects on control of nitric oxide emission in a hydrogen fueled SI engine

Though hydrogen fueled spark ignition engine can operate at high thermal efficiency with almost zero emission of HC and CO, the high level of _NOx${\mathrm{NO}}_x$ poses problems. The high combustion temperature and lean mixtures used are the reasons. In this work, the effect of _N2${\mathrm{N}}_2$, _CO2${\mathrm{CO}}_2$ and hot EGR gas as diluents in the intake charge to suppress NO emission in a manifold injected hydrogen fueled SI engine was studied. Nitrogen as a diluent is not so effective at low loads while inducting smaller amounts, but very effective at higher loads where the mixture becomes richer and the dilution effect (oxygen depletion) is significant. On other hand, carbon dioxide is a good diluent with relatively better thermal effect and diluent effect and effectively controls NO emission at all output regions. However this is at the expense of thermal efficiency. Recirculating hot exhaust gas which contains both _N2${\mathrm{N}}_2$ and steam comes in between _N2${\mathrm{N}}_2$ and _CO2${\mathrm{CO}}_2$ in terms of its effectiveness. On the whole _N2${\mathrm{N}}_2$ is the most effective as it has minimum impact on thermal efficiency for a given level of permissible NO emission. Thus it is felt that cold EGR could be a good option. In all cases, a good control system is necessary to supply correct quantity of diluent.     

An experimental study on performance and emission characteristics of a hydrogen fuelled spark ignition engine

In the present paper, the performance and emission characteristics of a conventional four cylinder spark ignition (SI) engine operated on hydrogen and gasoline are investigated experimentally. The compressed hydrogen at 20  MPa has been introduced to the engine adopted to operate on gaseous hydrogen by external mixing. Two regulators have been used to drop the pressure first to 300 kPa, then to atmospheric pressure. The variations of torque, power, brake thermal efficiency, brake mean effective pressure, exhaust gas temperature, and emissions of _NOx${\mathrm{NO}}_x$, CO, _CO2${\mathrm{CO}}_2$, HC, and _O2${\mathrm{O}}_2$ versus engine speed are compared for a carbureted SI engine operating on gasoline and hydrogen. Energy analysis also has studied for comparison purpose. The test results have been demonstrated that power loss occurs at low speed hydrogen operation whereas high speed characteristics compete well with gasoline operation. Fast burning characteristics of hydrogen have permitted high speed engine operation. Less heat loss has occurred for hydrogen than gasoline. _NOx${\mathrm{NO}}_x$ emission of hydrogen fuelled engine is about 10 times lower than gasoline fuelled engine. Finally, both first and second law efficiencies have improved with hydrogen fuelled engine compared to gasoline engine. It has been proved that hydrogen is a very good candidate as an engine fuel. The obtained data are also very useful for operational changes needed to optimize the hydrogen fueled SI engine design.     

Combustion behaviors of a direct-injection engine operating on various fractions of natural gas–hydrogen blends

Combustion behaviors of a direct injection engine operating on various fractions of natural gas–hydrogen blends were investigated. The results showed that the brake effective thermal efficiency increased with the increase of hydrogen fraction at low and medium engine loads and high thermal efficiency was maintained at the high engine load. The phase of the heat release curve advanced with the increase of hydrogen fraction in the blends. The rapid combustion duration decreased and the heat release rate increased with the increase of hydrogen fraction in the blends. This phenomenon was more obviously at the low engine speed, suggesting that the effect of hydrogen addition on the enhancement of burning velocity plays more important role at relatively low cylinder air motion. The maximum mean gas temperature and the maximum rate of pressure rise increased remarkably when the hydrogen volumetric fraction exceeds 20% as the burning velocity increases exponentially with the increase of hydrogen fraction in fuel blends. Exhaust HC and _CO2${\mathrm{CO}}_2$ concentrations decreased with the increase of the hydrogen fraction in fuel blends. Exhaust _NOx${\mathrm{NO}}_x$ concentration increased with the increase of hydrogen fraction at high engine load. The study suggested that the optimum hydrogen volumetric fraction in natural gas–hydrogen blends is around 20% to get the compromise in both engine performance and emissions.     

The ignition,combustion and flame structure of carbon monoxide/hydrogen mixtures. Note 1: Detailed kinetic modeling of syngas combustion also in presence of nitrogen compounds

The kinetic characterization of the _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ system is of interest right now due mainly to its role in sustainable combustion processes. The aim of this paper is to revise and validate a detailed kinetic model of hydrogen and carbon monoxide mixture combustion with particular focus not only on _NOx${\mathrm{NO}}_x$ formation but also on interactions with nitrogen species. Model predictions and experimental measurements are discussed and compared across a wide range of operating conditions. This study moves from the detailed analysis of species profiles in syngas oxidation in flow reactor and laminar premixed flames to global combustion properties (ignition delay times and laminar flame speeds) by referring to a large set of literature data. According to recent literature, the validation of the kinetic scheme confirmed there was a need to slightly modify the kinetic parameters of two relevant _CO2${\mathrm{CO}}_2$ formation reactions (CO+OH=_CO2+H$\mathrm{CO}+\mathrm{OH}={\mathrm{CO}}_2+\mathrm{H}$ and CO+O+M=_CO2+M$\mathrm{CO}+\mathrm{O}+\mathrm{M}={\mathrm{CO}}_2+\mathrm{M}$) and of reaction HONO+OH=_NO2+_H2O$\mathrm{HONO}+\mathrm{OH}={\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O}$.     

Experimental study on thermal efficiency and emission characteristics of a lean burn hydrogen enriched natural gas engine

In order to analyze the effect of hydrogen addition on natural gas (NG) engine's thermal efficiency and emission, an experimental research was conducted on a spark ignition NG engine using variable composition hydrogen/CNG mixtures (HCNG). The results showed that hydrogen enrichment could significantly extend the lean operation limit, improve the engine's lean burn ability, and decrease burn duration. However, nitrogen oxides (NO_x)$({\text{NO}}_x)$ were found to increase with hydrogen addition if spark timing was not optimized according to hydrogen's high burn speed. Also found when spark timing was set at constant was that hydrogen addition actually increases heat transfer out of the cylinder due to smaller quenching distance and higher combustion temperature, thus is not good to improve thermal efficiency if combined with the effect of non-ideal spark timing. But if spark timing was retarded to MBT, taking advantage of hydrogen's high burn speed, _NOx${\mathrm{NO}}_x$ emissions exhibited no obvious increase after hydrogen addition and engine thermal efficiency increased with the increase of hydrogen fraction. Unburned hydrocarbon always decreased with the increase of hydrogen fraction.     

Biodiesel,emulsified biodiesel and dimethyl ether as pilot fuels for natural gas fuelled engines

Dual-fuelling in compression–ignition (CI) engines is a mode of combustion where a small pilot injection of high-cetane fuel (i.e. diesel) ignites a premixed high-octane fuel (i.e. methane) and air mixture. This allows conventional CI engines to lower their emissions of smoke and nitrogen oxides (NO_x)$({\text{NO}}_x)$ while maintaining their high thermal efficiencies. However, poor ignitability of the main fuel–air charge results in increased emissions of unburnt hydrocarbons (HC) and carbon monoxide (CO). Conventional pilot fuels such as diesel and biodiesel (methyl esters transesterified from raw plant oil) have been researched extensively in prior work, showing that in terms of performance and emissions they perform fairly similarly. This is because the physical, chemical and combustion properties of various methyl esters are comparable to those of conventional diesel. In order to reduce these emissions of HC and CO, alternative pilot fuels need to be considered. As fuels employed during normal CI engine operation, both dimethyl ether (DME, a gaseous CI engine fuel) and water-in-fuel emulsions (conventional biodiesel mixed with varying concentrations of water) have shown that they reduce smoke and _NOx${\mathrm{NO}}_x$ emissions significantly, while improving combustion quality. In this work, the performance of DME and water-in-biodiesel emulsions as pilot fuels was assessed. It was seen that the water-in-biodiesel emulsions did not perform as well as expected, as increased HC and CO emissions coupled with a mild change in _NOx${\mathrm{NO}}_x$ levels was encountered (compared to conventional pilot fuel, in this case neat biodiesel). The emulsions performed very poorly as pilot fuels below a certain BMEP threshold. DME, while producing higher levels of HC and CO than neat biodiesel, managed to reduce _NOx${\mathrm{NO}}_x$ significantly compared to neat biodiesel. Emissions of HC and CO, while higher than neat biodiesel, were not as high as levels seen with the emulsions. Thermal efficiency levels were generally maintained with the liquid pilot fuels, with the DME pilot producing comparatively lower levels.     

Hydrogen production from biomass coupled with carbon dioxide capture: The implications of thermodynamic equilibrium

In this work we report on the consequences of thermodynamic equilibrium for hydrogen (_H2)$({\mathrm{H}}_2)$ generation via steam gasification of biomass, coupled with in situ carbon dioxide (_CO2)$({\mathrm{CO}}_2)$ capture. Calcium oxide (CaO) is identified as a suitable sorbent for CO₂ capture, capable of absorbing CO₂ to very low concentrations, at temperatures and pressures conducive to the gasification of biomass. The proposed process exploits the reversible nature of the CO₂ capture reaction and leads to the production of a concentrated stream of CO₂, upon regeneration of the sorbent. We develop a thermodynamic equilibrium model to investigate fundamental reaction parameters influencing the output of H₂-rich gas. These are: (i) reaction temperature, (ii) reaction pressure, (iii) steam-to-biomass ratio, and (iv) sorbent-to-biomass ratio. Based on the model, we predict a maximum H₂ concentration of 83%-mol, with a steam-to-biomass ratio of 1.5 and a Ca-to-C ratio of 0.9. Contrary to previous experimental studies, this maximum H₂ output is reported at atmospheric pressure. Model predictions are compared with an experimental investigation of the pyrolysis of pure cellulose and the reactivity of CaO through multiple CO₂ capture and release cycles using a thermogravimetric analyser, coupled with a mass spectrometer (TGA–MS). On this basis, we demonstrate the applicability of thermodynamic equilibrium theory for the identification of optimal operating conditions for maximising H₂ output and CO₂ capture.     

CO2 reforming of CH4 by combination of thermal plasma and catalyst

Experiments on synthesis gas preparation from dry reforming of methane by carbon dioxide with thermal plasma only and cooperation of thermal plasma with commercial catalysts have been performed. In all experiments, nitrogen gas was used as the plasma gas to form a high-temperature jet injected into a tube reactor. A mixture of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$ was fed vertically into the jet. Both kinds of experiments were conducted in the same conditions, such as total flux of feed gases, the molar ratio of _CH4/_CO2${\mathrm{CH}}_4/{\mathrm{CO}}_2$, and the plasma power except with or without catalysts in the tube reactor. Higher conversion of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$, higher selectivity of _H2${\mathrm{H}}_2$ and CO, and higher specific energy of the process were achieved by thermal plasma with catalysts. For example, the conversions of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$ were high to 96.33% and 84.63%, and the selectivies of CO and _H2${\mathrm{H}}_2$ were also high to 91.99% and 74.23%, respectively. Both were 10–20%$10–20\%$ higher than those by thermal plasma only.     

Increase of passenger car engine efficiency with low engine-out emissions using hydrogen–natural gas mixtures: A thermodynamic analysis

In this study a state of the art passenger car natural gas engine was optimised for hydrogen natural gas mixtures and high exhaust gas recirculation (EGR) rates in the part load domain. With optimal combinations of spark timing (ST) and EGR rate the achievements are significant efficiency increase with substantially lower engine-out _NOx${\mathrm{NO}}_x$ while total unburned hydrocarbons or CO-engine-out emissions are not affected. Comprehensive investigations of the parameter space using design of experiments (DoE) algorithms provided a complete picture of the potential of such applications. Combustion analysis on the other hand allowed to identify improvements on the basis of accelerated combustion caused by the hydrogen as well as the reduced gas exchange losses due to EGR and associated less required throttling for a given engine output. The best combinations of EGR rate, hydrogen-fraction in the fuel and ST exhibited optimal in-cylinder pressure characteristics accompanied by moderate combustion peak temperatures and low expansion cylinder temperatures.     

Hydrogen production by using manganese ferrite: Evidences and benefits of a multi-step reaction mechanism

Hydrogen production by water splitting with _MnFe2O4/_Na2CO3${\mathrm{MnFe}}_2{\mathrm{O}}_4/{\mathrm{Na}}_2{\mathrm{CO}}_3$ system was studied at 973 K. An intermediate phase, resulting from decarbonatation of _MnFe2O4/_Na2CO3${\mathrm{MnFe}}_2{\mathrm{O}}_4/{\mathrm{Na}}_2{\mathrm{CO}}_3$ mixture in inert atmosphere, proved to be effective in hydrogen reduction from water with stoichiometric yield. The presence of a highly reactive intermediate phase suggests the feasibility of a high efficiency, three-step, thermochemical cycle for hydrogen production. In fact, the possibility of obtaining _CO2${\mathrm{CO}}_2$ separately from the gases mixture dramatically enhances process efficiency.     

Effects of hydrogen addition and cylinder cutoff on combustion and emissions performance of a spark-ignited gasoline engine under a low operating condition

Because of the low combustion temperature and high throttling loss, SI (spark-ignited) engines always encounter dropped performance at low load conditions. This paper experimentally investigated the co-effect of cylinder cutoff and hydrogen addition on improving the performance of a gasoline-fueled SI engine. The experiment was conducted on a modified four-cylinder SI engine equipped with an electronically controlled hydrogen injection system and a hybrid electronic control unit. The engine was run at 1400 rpm, 34.5 Nm and two cylinder cutoff modes in which one cylinder and two cylinders were closed, respectively. For each cylinder closing strategy, the hydrogen energy fraction in the total fuel (βH₂)$\left({\beta }_{{\text{H}}_2}\right)$ was increased from 0% to approximately 20%. The test results demonstrated that engine indicated thermal efficiency was effectively improved after cylinder cutoff and hydrogen addition, which rose from 34.6% of the original engine to 40.34% of the engine operating at two-cylinder cutoff mode and βH₂=20.41%${\beta }_{{\text{H}}_2}=20.41\%$. Flame development and propagation periods were shortened with the increase of the number of closed cylinders and hydrogen blending ratio. The total cooling loss for all working cylinders, and tailpipe HC (hydrocarbons), CO (carbon monoxide) and CO₂ (carbon dioxide) emissions were reduced whereas tailpipe NO_x (nitrogen oxide) emissions were increased after hydrogen addition and cylinder closing.     

Lifecycle impacts of natural gas to hydrogen pathways on urban air quality

In this paper we examine the potential air quality impacts of hydrogen transportation fuel from a lifecycle analysis perspective, including impacts from fuel production, delivery, and vehicle use. We assume that hydrogen fuel cell vehicles are introduced in a specific region, Sacramento County, California. We consider two levels of market penetration where 9% or 20% of the light duty fleet are hydrogen fuel cell vehicles. The following three natural gas to hydrogen supply pathways are assessed in detail and compared in terms of emissions and the resulting changes in ambient air quality: (1) onsite hydrogen production; (2) centralized hydrogen production with gaseous hydrogen pipeline delivery systems; and (3) centralized hydrogen production with liquid hydrogen truck delivery systems. All the pathways examined use steam methane reforming (SMR) of natural gas to produce hydrogen. The source contributions to incremental air pollution are estimated and compared among hydrogen pathways. All of the hydrogen pathways result in extremely low contributions to ambient air concentrations of _NOx${\mathrm{NO}}_x$, CO, particulates, and _SOx${\mathrm{SO}}_x$, typically less than 0.1% of the current ambient pollution for both levels of market penetration. Among the hydrogen supply options, it is found that the central SMR with pipeline delivery systems is the lowest pollution option available provided the plant is located to avoid transport of pollutants into the city via prevailing winds. The onsite hydrogen pathway is comparable to the central hydrogen pathway with pipeline systems in terms of the resulting air pollution. The pathway with liquid hydrogen trucks has a greater impact on air quality relative to the other pathways due to emissions associated with diesel trucks and electricity consumption to liquefy hydrogen. However, all three hydrogen pathways result in negligible air pollution in the region.     

Hydrogen production from biogas using hot slag

Possibility of hydrogen production from biogas using hot slag has been studied, in which decomposition rate of _CO2${\mathrm{CO}}_2$–_CH4${\mathrm{CH}}_4$ in a packed bed of granulated slag was measured at constant flow-rate and pressure. The molten slag, discharged at high temperature over 1700 K from smelting industries such as steelmaking or municipal waste incineration. It has enough potential for replacing energy required for hydrogen production due to the catalytic steam reforming or carbon decomposition of hydrocarbon. However, heat recovery of hot slag has never been established. Therefore, the objective of this work is to generate hydrogen from methane using heated slag particles as catalyst, in which the effect of temperature on the hydrogen generation was mainly investigated at range from 973 to 1273 K. In the experiments a mixed gas of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$ was continuously introduced into the packed bed of hot slag at constant flow-rate and atmospheric pressure and then the outlet gas was monitored by gas chromatography. The results indicate that slag acted as not only thermal media but also good catalyst, for promoting decomposition. The product gases were mainly hydrogen and carbon monoxide with/without solid carbon deposition on the surface of slag, depending on the reaction temperature. Increasing temperature led to large hydrogen generation with decreasing un-reacted methane in the outlet gas, at when the largest methane conversion was about 96%. The results suggested a new energy-saving process of hydrogen production, in which the waste heat from molten slag can replace the energy required for hydrogen production, reducing carbon dioxide emission.     

Hydrogen as an ignition-controlling agent for HCCI combustion engine by suppressing the low-temperature oxidation

Homogeneous charge compression ignition (HCCI) combustion enables internal combustion engines to achieve higher thermal efficiency and lower _NOx${\mathrm{NO}}_x$ emission than with conventional combustion systems. Controlling the ignition timing in accordance with the operating conditions is crucial for utilizing HCCI combustion engines. Adding hydrogen-containing gas is known to retard the autoignition of dimethyl ether (DME) considerably. The effective ignition control by hydrogen can expand the operation range of equivalence ratios and engine loads in HCCI combustion. This research investigated the mechanisms in the ignition control by the chemical kinetics analysis. The results show that the retarded ignition can be attributed to a consumption of OH by hydrogen during low-temperature oxidation of DME. The decreased OH concentration leads to retarded heat release and delays the onset of the high-temperature oxidation.     

Experimental study of combustion of hydrogen–syngas/methane fuel mixtures in a porous burner

Lean premixed combustion of hydrogen–syngas/methane fuel mixtures was investigated experimentally to demonstrate fuel flexibility of a two-section porous burner. The un-insulated burner was operated at atmospheric pressure. Combustion was stabilized at the interface of silicon-carbide coated carbon foam of 26 pores per centimeter (ppcm) and 4 ppcm. Methane (CH₄) content in the fuel was decreased from 100% to 0% (by volume), with the remaining amount split equally between carbon monoxide (CO) and hydrogen (H₂), the two reactive components of the syngas. Experiments for different fuel mixtures were conducted at a fixed air flow rate, while the fuel flow rate was varied to obtain a range of adiabatic flame temperatures. The CO and nitric oxide (_NOx${\mathrm{NO}}_x$) emissions were measured downstream of the porous burner, in the axial direction to identify the post-combustion zone and in the transverse direction to quantify combustion uniformity. For a given adiabatic flame temperature, increasing H₂/CO content in the fuel mixture decreased both the CO and _NOx${\mathrm{NO}}_x$ emissions. Presence of H₂/CO in the fuel mixture also decreased temperature near the lean blow-off limit, especially for higher percentages of CO and H₂ in the fuel.     

A review of the interference of carbon containing fly ash with air entrainment in concrete

Industrial utilization of fly ash from pulverized coal combustion plays an important role in environmentally clean and cost effective power generation. Today, the primary market for fly ash utilization is as pozzolanic additive in the production of concrete. However, the residual carbon in fly ash may interfere with air entraining admixtures (AEAs) added to enhance air entrainment in concrete in order to increase its workability and resistance toward freezing and thawing conditions. The problem has increased with implementation of low-_NOx${\mathrm{NO}}_x$ combustion technologies.