Development of 1 kW SOFC power package for dual-fuel operation

A compact SOFC power generation system was developed by integrating a 1 kW SOFC stack and balance-of-plant. The system was designed for dual-fuel operation using both natural gas (NG) and liquefied petroleum gas (LPG). An adiabatic pre-reformer was employed in a fuel processing system to convert C₂₊ hydrocarbons in the fuel into CH₄-rich gas which was further processed in a main reformer to produce H₂-rich gas for the SOFC stack. The SOFC system was operated for 350 h under thermally self-sustaining condition, and on-load fuel switching from NG to LPG was carried out during the operation. The system performance was not significantly affected by NG/LPG composition ratios and the performance was stable during continuous operation in NG or LPG.     

Hydrogen supplemented natural gas effect on a DI diesel engine operating under dual fuel mode with a biodiesel pilot fuel

In order to slow down the continuing environmental deterioration, regulations for pollutant emissions limitations are increasingly rigorous. The development of new alternative fuels for internal combustion engines is a very interesting solution not only to overcome the pollution problem but also because of the petroleum shortage. In this context, the present work investigates the improvement of a DI diesel engine operating at constant speed (1500 rpm) and under dual fuel mode with eucalyptus biodiesel and natural gas (NG) enriched by various H₂ quantities (15, 25 and 30 by v%). The eucalyptus biodiesel quantity injected into the engine cylinder is kept constant, to supply around 10% of the engine nominal power, for all examined engine loads. The engine load is further increased using only the gaseous fuel (NG+H₂), which is introduced with the intake air. The effect of H₂/NG blending ratio on the combustion parameters, performance and pollutant emissions of the engine is investigated and compared with those of pure NG case. An important benefit in terms of brake specific fuel consumption, reaching a decrease of 4–10% with the 25% H₂ blend compared to the pure NG case, is achieved. Concerning the pollutant emissions, NG enrichment with H₂ is an efficient solution to enhance the combustion process and hence reduce carbon monoxide, unburned hydrocarbon and soot emissions at high loads where they are important for pure NG. However for the nitrogen oxide emissions, NG blending with H₂ is attractive only at low and medium loads where their levels are lower than pure NG.     

MILD combustion of hydrogenated biogas under several operating conditions in an opposed jet configuration

MILD combustion of biogas takes its importance firstly from the combustion process that diminishes significantly fuel consumption and reduces emissions and secondly from the use of biogas which is a renewable fuel. In this paper, the influence of several operating conditions (namely biogas composition, hydrogen enrichment and oxidizer dilution) is studied on flame structure and emissions. The investigation is conducted in MILD regime with a special focus on chemical effects of CO₂ in the oxidizer. Opposed jet diffusion combustion configuration is adopted. The combustion kinetics is described by the Gri 3.0 mechanism and the Chemkin code is used to solve the problem.It is found that oxygen reduction has a significant effect on flame temperature and emissions while less sensitivity corresponds to hydrogen enrichment in MILD combustion regime. Temperature and species are considerably reduced by oxygen decrease in the oxidizer and augmented by hydrogen addition to the fuel. The maximum values of temperature and species are not influenced by the composition of the biogas in MILD regime. Blending biogas with hydrogen can be used to sustain MILD combustion at very low oxygen concentration in the fuel.In MILD combustion regime, the chemical effect of CO₂ in the oxidizer stream reduces considerably the flame temperature and species production, except CO which is enhanced. For high amounts of CO₂ in the oxidizer, the chemical effect of CO₂ becomes negligible.     

An experimental investigation of incomplete combustion of gaseous fuels of a heavy-duty diesel engine supplemented with hydrogen and natural gas

This paper investigates the emissions of the unburned gaseous fuels of a heavy-duty diesel engine converted to operate under natural gas (NG)-diesel and hydrogen (H₂)-diesel dual fuel combustion mode. The detailed effects of the addition of H₂, NG, engine load, and engine speed on the exhaust emissions of the unburned H₂, methane (CH₄), and carbon monoxide (CO) were experimentally investigated. The combustion efficiencies of CH₄ and H₂ supplemented were also examined and compared.     

Mechanisms of NO formation in MILD combustion of CH4/H2 fuel blends

The mechanisms of formation and destruction of NO in MILD combustion of CH₄/H₂ fuels blends are investigated both experimentally and numerically. Experiments are carried out at a lab-scale furnace with the mass fraction of hydrogen in fuel ranging from 0% to 15%; furnace temperature, extracted heat and exhaust NO_x emissions are measured. Detailed chemical kinetics calculations utilizing computational fluid dynamics (CFD) and well-stirred reactor (WSR) are performed to better analyze and isolate the different mechanisms.     

On-board LPG reforming system for an LPG · hydrogen mixed combustion engine

In this study, we evaluated the properties of a reforming catalyst system for generating hydrogen from liquified petroleum gas (LPG) fuel and supplying hydrogen to an LPG engine. The fuel supply system of the LPG engine was modified in order to supply LPG to a reforming catalyst prior to combustion. A test apparatus was also built to evaluate the performance of a reforming catalyst system. Gas chromatography was used to measure H₂, N₂, O₂, CH₄, and CO emissions, while CO₂ emissions were measured using an exhaust gas analyzer. The products concentration of the reforming reactions according to reforming fuel quantity and air flow was analyzed. In actual engine operating conditions, H₂ yield and air flow were proportional, whereas H₂ yield and fuel reforming fuel quantity were inversely proportional. The experimental results of the reforming reaction under various conditions will be used as the basic data for integrating the reforming catalyst system into an actual operating engine.     

Reduction in nitrogen oxides emissions by MILD combustion of dried sludge

Demands for the thermal treatment of sewage sludge are increasing due to the regulation of its ocean disposal and the desire to recover its potential energy. Because of the high nitrogen content in sewage sludge, one of the concerns about its combustion is a potential increase in NO_x emissions. Although a number of studies have been conducted to reduce NO_x emissions by combustion modifications, very few studies have addressed the combustion of dried sludge. In this study, a combustion technique called moderate or intense low oxygen dilution (MILD) was applied to the combustion of dried sludge with the goal of reducing NO_x emissions. MILD combustion of dried sludge was tested using both our laboratory-scale vertical combustor with internal circulation and our horizontal cyclone combustor with external circulation. Tests were conducted to find suitable operating conditions and to demonstrate the stable MILD combustion of dried sludge. From these tests, fuel and air flow patterns were found to be an important factor in maintaining stable MILD combustion, and the horizontal cyclone combustor demonstrated excellent performance in the reduction of NO_x emissions by the MILD combustion of dried sludge.     

Design and performance evaluation of an innovative small scale combined cycle cogeneration system

This paper deals with an innovative natural gas (NG) combined cycle cogeneration system (150-kW_e, 192 kW_t). The system is made up of a combination of two interconnected combined heat and power (CHP) systems: a reciprocating internal combustion engine cogenerator (ICE CHP) as the topping cycle and a Rankine cycle cogenerator (RC CHP) which operates as the bottoming cycle on the exhaust gases from the ICE. The expander technology chosen for the Rankine cycle prime mover is a reciprocating single expansion steam engine with three cylinders in a radial architecture. The ICE is an automotive derived internal combustion engine with a high part-load electrical efficiency, due to a variable speed operation strategy and reduced emissions.     

Effect of syngas composition on combustion and exhaust emission characteristics in a pilot-ignited dual-fuel engine operated in PREMIER combustion mode

The objective of this study was to investigate the performance and emissions of a pilot-ignited, supercharged, dual-fuel engine powered by different types of syngas at various equivalence ratios. It was found that if certain operating conditions were maintained, conventional engine combustion could be transformed into combustion with two-stage heat release. This mode of combustion has been investigated in previous studies with natural gas, and has been given the name PREmixed Mixture Ignition in the End-gas Region (PREMIER) combustion. PREMIER combustion begins as premixed flame propagation, and then, because of mixture autoignition in the end-gas region, ahead of the propagating flame front, a transition occurs, with a rapid increase in the heat release rate. It was determined that the mass of fuel burned during the second stage affected the rate of maximum pressure rise. As the fuel mass fraction burned during the second stage increased, the rate of maximum pressure rise also increased, with a gradual decrease in the delay between the first increase in the heat release rate following pilot fuel injection and the point when the transition to the second stage occurred. The H₂ and CO₂ content of syngas affected the engine performance and emissions. Increased H₂ content led to higher combustion temperatures and efficiency, lower CO and HC emissions, but higher NOx emissions. Increased CO₂ content influenced performance and emissions only when it reached a certain level. In the most recent studies, the mean combustion temperature, indicated thermal efficiency, and NOx emissions decreased only when the CO₂ content of the syngas increased to 34%. PREMIER combustion did not have a major effect on engine cycle-to-cycle variation. The coefficient of variation of the indicated mean effective pressure (COV_IMEP) was less than 4% for all types of fuel at various equivalence ratios, indicating that the combustion was within the stability range for engine operation.     

Effect of fuel composition on jet flames in a heated and diluted oxidant stream

The role of hydrogen addition on the structure of the Moderate or Intense Low oxygen Dilution (MILD) combustion regime is examined using a combination of experimental techniques and laminar flame calculations. Laser diagnostic imaging is used to simultaneously reveal the in situ distribution of the hydroxyl radical (OH), formaldehyde (H₂CO), and temperature using the Jet in Hot Coflow (JHC) burner. The fuels considered are natural gas, ethylene, and LPG (each diluted with hydrogen 1:1 by volume). Hydrogen addition to the primary fuel was found necessary to stabilise the flames. Further to the role of hydrogen in the stabilisation of the flames, hydrogen addition also leads to the reaction zone exhibiting similar structure for different primary fuel types. The independence of the reaction zone structure with hydrogen addition suggests that a wide variety of fuels may be usable for achieving MILD combustion.     

Operational characteristics of a parallel jet MILD combustion burner system

This study describes the performance and stability characteristics of a parallel jet MILD (Moderate or Intense Low-oxygen Dilution) combustion burner system in a laboratory-scale furnace, in which the reactants and exhaust ports are all mounted on the same wall. Thermal field measurements are presented for cases with and without combustion air preheat, in addition to global temperature and emission measurements for a range of equivalence ratio, heat extraction, air preheat and fuel dilution levels. The present furnace/burner configuration proved to operate without the need for external air preheating, and achieved a high degree of temperature uniformity. Based on an analysis of the temperature distribution and emissions, PSR model predictions, and equilibrium calculations, the CO formation was found to be related to the mixing patterns and furnace temperature rather than reaction quenching by the heat exchanger. The critical equivalence ratio, or excess air level, which maintains low CO emissions is reported for different heat exchanger positions, and an optimum operating condition is identified. Results of CO and NO_x emissions, together with visual observations and a simplified two-dimensional analysis of the furnace aerodynamics, demonstrate that fuel jet momentum controls the stability of this multiple jet system. A stability diagram showing the threshold for stable operation is reported, which is not explained by previous stability criteria.     

Experimental investigation on NG dual fuel engine improvement by hydrogen enrichment

The crude oil graduate depletion, as well as aspects related to environmental pollution and global warming instigated many researches concerning alternative fuels. Natural gas (NG) is one of the most attractive available fuels. A promising technique for its use in internal combustion engines is the dual fuel concept. One of the main problems with this technique is that, at low loads, the engine efficiency decreases compared to conventional diesel. The unburned hydrocarbons and carbon monoxide emissions are also higher in dual fuel mode. An effective method to compensate the demerits of limited lean-burn ability and slow burning velocity of NG is to mix it with a fuel that possesses wide flammability limit and fast burning velocity. Hydrogen (H₂) is thought to be the best gaseous candidate for natural gas.In the present work, NG enrichment with various H₂ blends is investigated as a technique for improving dual fuel mode, especially at low loads. Impact on engine performance and emissions is experimentally examined. Total BSFC is considerably reduced. An important benefit in terms of BTE, reaching to increase a 12% with the 10%H₂ blend compared to the pure NG case, is also achieved. THC and CO emissions are in general reduced as a result of the improvement of gaseous fuel utilization. CO₂ emissions are also in general reduced. Even though a slight increase is in overall observed for NO_x emissions, it's almost insignificant.     

An experimental investigation of NO2 emission characteristics of a heavy-duty H2-diesel dual fuel engine

This paper investigated the nitrogen dioxide (NO₂) emissions of a heavy-duty diesel engine operated in hydrogen (H₂)-diesel dual fuel combustion mode with H₂ supplemented into the intake air. Preliminary measurements using the 13-mode European Stationary Cycle (ESC) demonstrated the significant effect of H₂ addition on the emissions of NO₂. The detailed effects of H₂ addition and engine load on NO₂ emissions were examined at 1200 RPM. The addition of a small amount of H₂ increased substantially the emissions of NO₂ and the NO₂/NO_x ratio, especially at low load. Increasing the engine load was found to inhibit the enhancing effect of H₂ on the conversion of NO to NO₂ with the maximum NO₂/NO_x ratio observed at lower H₂ concentration. The maximum NO₂ emissions of the H₂-diesel dual fuel operation were three (at 70% load) to five (at 10% load) times that of diesel operation. Further increasing the addition of H₂ beyond the point with maximum NO₂ emissions still produced more NO₂ than for diesel-only operation. Based on the experimental data obtained, the engine load and maximum averaged bulk mixture temperature were not the main factors dominating the formation of NO₂ in the H₂-diesel dual fuel engine. A preliminary analysis demonstrated the significant effect of the unburned H₂ on NO₂ emissions. When mixed with the hot combustion product, the unburned H₂ that survived the main combustion process might further oxidize to raise the HO₂ levels and enhance the conversion of NO to NO₂. In comparison, the changes in the combustion process including the start of combustion, combustion duration and maximum heat release rate may not contribute substantially to the increased NO₂ emissions observed.     

Blending blue hydrogen with natural gas for direct consumption: Examining the effect of hydrogen concentration on transportation and well-to-combustion greenhouse gas emissions

Jurisdictions are looking into mixing hydrogen into the natural gas (NG) system to reduce greenhouse gas (GHG) emissions. Earlier studies have focused on well-to-wheel analysis of H₂ fuel cell vehicles, using high-level estimates for transportation-based emissions. There is limited research on transportation emissions of hythane, a blend of H₂ and NG used for combustion. An in-depth analysis of the pipeline transportation system was performed for hythane and includes sensitivity and uncertainty analyses. When hythane with 15% H₂ is used, transportation GHG emissions (gCO2eq/GJ) increase by 8%, combustion GHG emissions (gCO2eq/GJ) decrease by 5%, and pipeline energy capacity (GJ/hr) decreases by 11% for 50–100 million m³/d pipelines. Well-to-combustion (WTC) emissions increase by 2.0% without CCS, stay the same with a 41% CCS rate, decrease by 2.8% for the 100% CCS scenario, and decrease by 3.6% in the optimal CO₂-free scenario. While hythane contains 15% H₂ by volume only 5% of the gas’ energy comes from H₂, limiting its GHG benefit.     

Effect of H2 addition on combustion and exhaust emissions in a heavy-duty diesel engine with EGR

The effect of the addition of hydrogen (H₂) on the combustion process and nitric oxide (NO) formation in a H₂-diesel dual fuel engine was numerically investigated. The model developed using AVL FIRE as a platform was validated against the cylinder pressure and heat release rate measured with the addition of up to 6% (vol.) H₂ into the intake mixture of a heavy-duty diesel engine with exhaust gas recirculation (EGR). The validated model was applied to further explore the effect of the addition of 6%–18% (vol.) H₂ on the combustion process and formation of NO in H₂-diesel dual fuel engines. When the engine was at N = 1200 rpm and 70% load, the simulation results showed that the addition of H₂ prolonged ignition delay, enhanced premixed combustion, and promoted diffusion combustion of the diesel fuel. The maximum peak cylinder pressure was observed with addition of 12% (vol.) H₂. In comparison, the maximum peak heat release rate was observed with the addition of 16% (vol.) H₂. The addition of H₂ was a crucial factor dominating the increased NO emissions. Meanwhile, the addition of H₂ reduced soot emissions substantially, which may be due to the reduced diesel fuel burned each cycle. Furthermore, proper combination of adding H₂ with EGR can improve combustion performance and reduce NO emissions.     

Performance and emissions characteristics of a lean-burn marine natural gas engine with the addition of hydrogen-rich reformate

The exhaust gas-fuel reforming technique known as reformed exhaust gas recirculation (REGR) can generate on-board hydrogen-rich gas mixture (i.e., reformate) by catalytic reforming of the exhaust gas and fuel added into the reformer and then recirculate the reformate into the engine cylinder, which can realize the combination of hydrogen-rich lean combustion and exhaust gas recirculation. The REGR technique can be employed to achieve efficient and stable lean-burn combustion for the marine engine fueled with natural gas (i.e., marine NG engine) and it is considered as an effective way to meet the stringent ship emissions regulations. In the present study, an experimental investigation into the effects of reformate addition ratio (R_re) and excess air ratio (λ) on the combustion and emissions characteristics of a marine NG engine under various loads was conducted, and the potential of applying the REGR technique in a marine NG engine to achieve low emissions (i.e., International Maritime Organization Tier Ⅲ emissions legislations for international ships) was discussed. The results indicate that the addition of the hydrogen-rich reformate gases can extend lean-burn limit. For a given λ, the flame development duration and rapid combustion duration decrease with the increase of R_re, and the combustion efficiency is improved. The brake specific NO_x emissions first increase and then decrease with the increase of R_re due to the competition between the combustion phase and total heat release value. The brake specific THC emissions decline with the increase of R_re, while the reverse holds for the brake specific CO emissions, and the behavior tends to be obvious under large λ. It is demonstrated that the combination of REGR and the lean-burn combustion strategy can improve the trade-off relationship between the NO_x emissions and brake specific fuel consumption of the marine NG engine to meet the IMO Tier Ⅲ NO_x emissions legislations and maintain relatively low brake specific fuel consumption.     

Effect of the combustion model and kinetic mechanism on the MILD combustion in an industrial burner fed with hydrogen enriched fuels

A numerical and experimental investigation of a burner operating in MILD combustion regime and fed with methane and methane-hydrogen mixtures (with hydrogen content up to 20% by wt.) is presented. Numerical simulations are performed with two different combustion models, i.e. the ED/FR and EDC models, and three kinetic mechanisms, i.e. global, DRM-19 and GRI-3.0. Moreover, the influence of molecular diffusion on the predictions is assessed. Results evidence the need of a detailed chemistry approach, especially with H₂, to capture the volumetric features of MILD combustion. The inclusion of molecular diffusion influences the prediction of H₂ distribution; however, the effects on the temperature field and on the major species are negligible for the present MILD combustion system. A simple NO formation mechanism based on the thermal and prompt routes is found to provide NO emissions in relatively good agreement with experimental observations only when applied on temperature fields obtained with the EDC model and detailed chemistry.     

Effects of hydrogen addition on combustion characteristics of a methane fueled MILD model combustor

Combined with need of the carbon emissions, the feasibility of Moderate or Intense Low-oxygen Dilution (MILD) combustion fueled with hydrogen/methane blends needs to be investigated. This paper discusses the pollutant emissions, the stable operating range and the flame morphology for a jet-induced MILD model combustor. The hydrogen/methane volume ratios range 0:10 to 5:5. The NO_x emissions are less than 5 ppm@15%O₂ when the hydrogen content is less than 50% by volume in the atmospheric conditions. The calculation using chemical reactor network (CRN) model demonstrates that the effect of heat loss on NO_x emissions increases as the adiabatic combustion temperature increases, which is consistent with the experimental results. The maximum OH1 signal intensity increased at higher hydrogen content, especially when the hydrogen content exceeds 30% by volume. Due to the increase in turbulent burning velocity and the enhancement in the reaction intensity, the reaction zones shrink with increasing hydrogen content. In addition, with increasing hydrogen content, the stable operation range of the combustor becomes narrower, and the stable combustion is not maintained when the hydrogen content exceeds 50% by volume. The findings of the paper help to further understand the effect of hydrogen content on the formation of MILD combustion in the jet-induced combustor.     

Effect of steam addition and distance between inlet nozzles on non-catalytic POX process under MILD combustion condition

Moderate or intensive low-oxygen dilution (MILD) combustion is a novel combustion technology with high efficiency and low emissions. Few studies have been performed on the application of this technology for partial oxidation processes. In this research, a Computational Fluid Dynamics study for the effect of different parameters on the natural gas partial oxidation under MILD combustion conditions has been carried out. The combustion chamber was in the form of cylinder with a diameter of 300 mm and a length of 1500 mm. The effect of parameters such as different kinetic mechanisms, adding ethane and propane to methane (shale gas feed), adding steam to the feed and distance (interval) between methane and oxygen nozzles were investigated. Results showed that addition of ethane and propane to methane increased the mole fraction of CO and C₂H₂ so that, in the case of mixed methane with ethane and propane compared to the case of pure methane, an increase of 18.75% and 12.93% was observed for CO and C₂H₂, respectively. In addition, with increasing the percentage of steam in the inlet feed at a constant flow rate, methane conversion increased so that it in the case of 30% inlet steam was 77.17%, which showed 11% promotion compared to the pure methane case. Also, increasing the distance between the fuel and oxidizer nozzles led to an increase in the maximum temperature in the combustion chamber.     

Towards the Hydrogen Economy in Paraguay: Green hydrogen production potential and end-uses

This study was conducted to estimate the potential for green H₂ in Paraguay. A total production potential of 22.5 × 10⁶ tons/year was obtained with a main contribution (93.34%) from solar photovoltaic. The greatest potential for producing H₂ from solar and wind resources is in the Western region, and from hydro resources is in the Eastern region of the country. Two end-uses of green H₂ were assessed: (1) automotive transportation, replacing gasoline and diesel; and (2) residential energy, replacing firewood and LPG for cooking in households across the country. In 16 of the 17 departments, green H₂ is able to replace the overall consumption of gasoline and diesel, as well as firewood and LPG. Finally, energy service cost (mobility), environmental aspects and CO₂ emissions were considered for three urban mobility technologies for the Metropolitan Area of Asunción. Results show that the mobility cost of fuel cell hybrid electric buses is still very high in comparison to diesel buses and battery electric buses. However, when a longer driving range is required, fuel cell hybrid electric buses could become a viable alternative in the long term. From an environmental point of view, green H₂ used in fuel cell hybrid electric buses has the potential to save about 96% of CO₂ emissions in comparison to diesel buses. It is concluded that the estimated green H₂ production potential favors the incorporation of the Hydrogen Economy in Paraguay.