Combustion and emission characteristics of a spray guided direct-injection spark-ignition engine fueled with natural gas-hydrogen blends

Combustion and emission characteristics of a spray guided direct-injection spark-ignition engine fueled with natural gas-hydrogen blends were investigated. Results show that the brake thermal efficiency increases with the increase of hydrogen fraction and it shows an increasing and then decreasing trend with advancing fuel-injection timing. For later injection timings, the beginning of heat release is advanced with increasing hydrogen fraction, while the beginning of heat release is advanced and then retarded with the increase of hydrogen fraction at earlier injection timings. The flame development duration, rapid combustion duration and total combustion duration decrease with increasing hydrogen fraction. Maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate show an increasing and then decreasing trend with the increase of hydrogen fraction. Brake NOx emission is increased and then decreased, while brake HC, CO and CO₂ emissions decrease with the increase of hydrogen fraction.     

Engine characteristics of emissions and performance using mixtures of natural gas and hydrogen

An evaluation was performed on the efficiency and emissions from an engine fuelled with compressed natural gas (CNG) and a mixture of natural gas and hydrogen, respectively. The mixtures of CNG and hydrogen were named HCNG.     

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 concentrations decreased with the increase of the hydrogen fraction in fuel blends. Exhaust _NOx 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.     

Experimental study of combustion performances and emissions of a spark ignition cogeneration engine operating in lean conditions using different fuels

This work presents an experimental study describing a six-cylinder spark ignition engine running with a lean equivalence ratio, high compression ratio, ignition delay and used in a cogeneration system (heat and electricity production). Three types of fuels; natural gas, pure methane and methane/hydrogen blend (85% CH₄ and 15% H₂ by volume), were used for comparison purposes. Each fuel has been investigated at 1500 rpm and for various engine loads fixed by electrical power output conditions. CO, CO₂, HC, and NOx emissions values, and exhaust gas temperature were measured. The effect of fuel composition on engine characteristics has been studied. The results show, that the hydrogen addition increased HC emissions (around 18%), as well as performance, whilst it reduced NO_x (around 31%), exhaust gas temperature, CO and CO₂.     

Experimental investigation on performance and emissions of a spark-ignition engine fuelled with natural gas–hydrogen blends combined with EGR

An experimental investigation on the influence of different hydrogen fractions and EGR rates on the performance and emissions of a spark-ignition engine was conducted. The results show that large EGR introduction decreases the engine power output. However, hydrogen addition can increase the power output at large EGR operation. Effective thermal efficiency shows an increasing trend at small EGR rate and a decreasing trend with further increase of EGR rate. In the case of small EGR rate, effective thermal efficiency is decreased with the increase of hydrogen fraction; while in the case of large EGR rate, thermal efficiency is increased with increasing of hydrogen fraction. For a specified hydrogen fraction, NO_x concentration is decreased with the increase of EGR rate and this effectiveness becomes more obviously at high hydrogen fraction. HC emission is increased with the increase of EGR rate and it decreases with the increase of hydrogen fraction. CO and CO₂ emissions show little variations with EGR rate, but they decrease with the increase of hydrogen fraction. The study shows that natural gas–hydrogen blend combining with EGR can realize high-efficiency and low-emission spark-ignition engine.     

不同点火时刻下天然气掺氢缸内直喷发动机燃烧与排放特性

在缸内直喷火花点火发动机上开展了天然气掺混0％-18％氢气的混合燃料不同点火时刻下的试验研究。结果表明：对于给定的喷射时刻和喷射持续期,点火时刻对发动机性能、燃烧和排放有较大影响,喷射结束时刻与点火时刻的间隔对直喷天然气发动机极为重要,喷射结束时刻与点火时刻的间隔缩短时,混合气分层程度高,燃烧速率快,热效率高。最大放热率等燃烧特征参数随点火时刻的提前而增加。HC排放随点火时刻的提前而下降,CO2和NOx排放随点火时刻的提前而增加,NOx排放的增加在大点火提前角下更明显。掺氢可降低HC排放,对CO和CO2排放影响不大。掺氢量大于10％时可提高天然气发动机热效率。     

The influences of hydrogen on the performance and emission characteristics of a heavy duty natural gas engine

Because blending hydrogen with natural gas can allow the mixture to burn leaner, reducing the emission of nitrogen oxide (NO_x), hydrogen blended with natural gas (HCNG) is a viable alternative to pure fossil fuels because of the effective reduction in total pollutant emissions and the increased engine efficiency.In this research, the performance and emission characteristics of an 11-L heavy duty lean burn engine using HCNG were examined, and an optimization strategy for the control of excess air ratio and of spark advance timing was assessed, in consideration of combustion stability. The thermal efficiency increased with the hydrogen addition, allowing stable combustion under leaner operating conditions. The efficiency of NO_x reduction is closely related to the excess air ratio of the mixture and to the spark advance timing. With the optimization of excess air ratio and spark advance timing, HCNG can effectively reduce NO_x as much as 80%.     

Computational modeling, validation, and utilization for predicting the performance, combustion and emission characteristics of hydrogen IC engines

Hydrogen-fueled internal combustion engines are considered to be more efficient and cleaner alternatives to their fossil-fueled counterparts. Reasonably fast and accurate predictive computational tools are essential for practical design, control and optimization of hydrogen engines. To serve for this broader purpose, a computational model, which has been widely used for gasoline and diesel engines, is investigated for its capability to simulate hydrogen engines. Specifically, fuel-specific sub-models are first incorporated by properly accounting for hydrogen’s distinct properties such as flame speed and burn rate. The accuracy of the model is then assessed by validating it in comparison to independent experimental data. Finally, it is utilized to quantify the environmental impact of exhaust gas recirculation. With these improvements, the present predictive model is shown to capture the measured engine performance and emission data well under different operating conditions. In particular, the variations of peak in-cylinder pressure, heat release rate, brake power, brake thermal efficiency, exhaust temperature, and NO_x emissions are predicted close to the measured values. With the addition of a proportional-integral-derivative controller to the engine model, exhaust gas recirculation level is varied, resulting in nearly an order of magnitude reduction in NO_x emissions during the present simulations.     

Thermophotovoltaic power generation systems using natural gas-fired radiant burners

Thermophotovoltaic (TPV) power generation in gas-fired furnaces is attracting technical attention. Considerable work has been done in the area of low bandgap GaSb cell-based TPV systems as well as silicon solar cell-based TPV systems. Previous investigations have shown that a radiant burner with a high conversion level of fuel to radiation energy must be developed to realize an efficient TPV system. In our work, we investigated different natural gas-fired radiant burners in order to raise the conversion of fuel energy to thermal radiation. These burners were used as radiation sources to establish and test two TPV prototype systems. It was found that for a non-surface combustion radiant burner, the radiation output can be enhanced using a thermal radiator with a porous structure. Also, we developed a cascaded radiant burner that generates two streams of radiation output. One stream illuminates silicon concentrator solar cells while the other drives low bandgap GaSb cells. In this way, useful radiation output and thus TPV system efficiency are significantly increased due to the cascaded utilization of combustion heat and optimized thermal management.     

Three-reactors chemical looping process for hydrogen production

This paper analyzes a novel process for producing hydrogen from natural gas, based on chemical looping (CL) techniques, allowing for intrinsic capture of carbon dioxide. The core of the process consists of a three-reactors CL system, where iron oxide particles are circulated to: (i) oxidize natural gas (thus providing, after cooling and water condensation, a CO₂ stream ready for sequestration), (ii) reduce steam, to produce hydrogen as the final product of the process, (iii) consume oxygen from an air stream, to sustain the thermal balance of the system.

The process is intrinsically very attractive, because it directly produces hydrogen and CO₂ from natural gas, by means of a process simpler than the conventional technologies with CO₂ capture capabilities. Hence, a significant potential for investment cost reduction can be anticipated.

However, to fully exploit the system potential, an efficient energy recovery from the gaseous streams exiting the reactors must be arranged, taking into account power and steam production needed to support internal consumptions. Therefore, after an introduction clarifying the concept and the scope of the system, as well as its basic chemistry, this paper presents a discussion of two plant configurations, including different integration levels with power production (fired gas turbine (GT) vs. unfired turbocharger) and/or heat recovery steam production methods (also considering steam compression devices). A comparison with “proven technology” plants, based on steam reforming, is also carried out. Due to the lack of reliable estimates of the investment costs for components to be developed from scratch (CL reactors), the analysis is limited to the thermodynamic and technological aspects. Results show, however, that an impressive potential exists for CL systems for hydrogen production, thus deserving substantial R&D activities in the near future.     

Effects on CHP plant efficiency of H2 production through partial oxydation of natural gas over two group VIII metal catalysts

Blending H₂ with natural gas in spark ignition engines can increase for electric efficiency. In-situ H₂ production for spark ignition engines fuelled by natural gas has therefore been investigated recently, and reformed exhaust gas recirculation (RGR) has been identified a potentially advantageous approach: RGR uses the steam and O₂ contained in exhaust gases under lean combustion, for reforming natural gas and producing H₂, CO, and CO₂. In this paper, an alternative approach is introduced: air gas reforming circulation (AGRC). AGRC uses directly the O₂ contained in air, rendering the chemical pathway comparable to partial oxidation. Formulations based on palladium and platinum have been selected as potential catalysts. With AGRC, the concentrations of the constituents of the reformed gas are approximately 25% hydrogen, 10% carbon monoxide, 8% unconverted hydrocarbons and 55% nitrogen. Experimental results are presented for the electric efficiency and exhaust gas (CO and HC) composition of the overall system (SI engine equipped with AGRC). It is demonstrated that the electric efficiency can increase for specific ratios of air to natural gas over the catalyst. Although the electric efficiency gain with AGRC is modest at around 0.2%, AGRC can be cost effective because of its straightforward and inexpensive implementation. Misfiring and knock were both not observed in the tests reported here. Nevertheless, technical means of avoiding knock are described by adjusting the main flow of natural gas and the additional flow of AGRC.