Efficiency improvement and superiority of steam injection in gas turbines

An open cycle gas turbine with a heat exchanger and its modifications have been studied. These modifications include the combinations of the gas turbine with a steam injection system and the gas turbine with a closed cycle steam turbine. The steam is generated by a waste heat boiler. It was found that in both cases the efficiency and the net output of the gas turbine increased considerably, of the order of 20–40%. In order to define the superiority regions of the systems studied on various ranges of power output, an economic analysis per unit power has been done. For short duration, intermittent type of operation the steam injection was found superior. Above this mode of operation, the operational modes of electric base and continuous were covered by the gas turbine combined with the steam turbine.     

Effects of direct water injection on engine performance in a hydrogen (H2)-fueled engine at varied amounts of injected water and water injection timing

In this paper, the effects of direct water injection (WI) on characteristics of combustion and emission for a hydrogen (H₂)-fueled spark ignition (SI) engine were experimentally investigated. The experiments conducted under different amounts of water injection (AWI) and varied water injection timing (WIT). The experimental results showed that in-cylinder pressure decreased, indicated thermal efficiency (ITE) increased, and the flame development (CA0-10) and propagation (CA10-90) periods prolonged when AWI raised. When AIW grew to 4.5 mg/cycle, Nitrogen oxides (NOx) expelled from the original engine decreased by 53.7% when excess air ratio (λ) was 1.15. Early WIT had positive effects on the reduction of NOx emissions. When WIT retarded, in-cylinder pressure increased, ITE decreased and CA0-10 and CA10-90 shortened, NOx emissions rapidly increased.     

A highly efficient six-stroke internal combustion engine cycle with water injection for in-cylinder exhaust heat recovery

A concept adding two strokes to the Otto or Diesel engine cycle to increase fuel efficiency is presented here. It can be thought of as a four-stroke Otto or Diesel cycle followed by a two-stroke heat recovery steam cycle. A partial exhaust event coupled with water injection adds an additional power stroke. Waste heat from two sources is effectively converted into usable work: engine coolant and exhaust gas. An ideal thermodynamics model of the exhaust gas compression, water injection and expansion was used to investigate this modification. By changing the exhaust valve closing timing during the exhaust stroke, the optimum amount of exhaust can be recompressed, maximizing the net mean effective pressure of the steam expansion stroke (MEP_steam). The valve closing timing for maximum MEP_steam is limited by either 1 bar or the dew point temperature of the expansion gas/moisture mixture when the exhaust valve opens. The range of MEP_steam calculated for the geometry of a conventional gasoline engine and is from 0.75 to 2.5 bars. Typical combustion mean effective pressures (MEP_combustion) of naturally aspirated gasoline engines are up to 10 bar, thus this concept has the potential to significantly increase the engine efficiency and fuel economy.     

压气机进口喷水湿压缩技术应用的限制因素

压气机进口喷水湿压缩技术近年来不但在电站燃气轮机上得到了广泛的应用,而且也开始应用在机械驱动燃气轮机上,同时在工业压气机上也开始了应用。湿压缩技术可以节省压缩耗功,是在炎热气候条件下恢复燃气轮机功率的有效措施。根据国内外分析和应用的经验,本文提出了在应用这项技术时应该注意的几个问题。首先是喷水颗粒尺寸的分布;其次应该注意喷水加湿的装置和过程不要引起压气机效率的降低以及其它值得注意的问题。     

The influence of water and steam injection on the performance of a recuperated cycle microturbine for combined heat and power application

Microturbines are promising power sources for small scale combined heat and power (CHP) systems. However, the power output and efficiency of microturbines decreases much as the ambient temperature increases. As a remedy to minimize the performance penalty at hot ambient conditions, the injection of water or steam into a microturbine CHP system was analyzed in this work. An analysis program to simulate the operation of a microturbine CHP system was set up and validated by using measured test data. The injection of hot water, which is generated at the heat recovery unit, at two different locations inside the microturbine was predicted. The generation of steam through the same heat recovery unit and its injection at the two locations was predicted as well. All the four cases provide sufficiently enhanced power output. Injection at the recuperator inlet exhibits a higher efficiency than injection at the combustor in both water and steam injections. Steam injection provides a higher power generation efficiency than water injection on the average. The injection of steam at the recuperator inlet is most promising in terms of power generation efficiency. However, water injection at the recuperator also enhances power generation efficiency while still providing thermal energy to some extent.     

Numerical investigation of water injection quantity and water injection timing on the thermodynamics,combustion and emissions in a hydrogen enriched lean-burn natural gas SI engine

Water direct injection into the cylinder is one of effective ways to suppress the combustion rate and knocking combustion in turbocharged SI engine. In this study, a detailed one-dimensional model coupled with the water direct injection was built by using the GT-Power according to the real tested hydrogen-enriched lean-burn natural gas (NG) SI engine, and validated against the experimental data. Then, a series of cases with various water injection quantity and injection timing were comprehensively investigated on the thermodynamics, combustion and emissions characteristics of the NGSI engine. The impact of the thermo-physical of the water were discussed in detailed by sweeping various water injection quantity and water injection timing. The results indicated that peak combustion pressure and peak heat release rate decreased with the increasing the water injection quantity. In addition, the 50% combustion location and peak combustion pressure location were retarded with the increasing the water injection quantity. As for the water injection timing, the peak combustion pressure and peak combustion temperature were slightly decreased with retarding the water injection timing. Apart from that, the indicated thermal efficiency decreased 4.03% and the equivalent fuel consumption increased 3.56% with injecting 60 mg water into the cylinder compared the case without water injection. Furthermore, the indicated thermal efficiency decreased 4.68% and the equivalent fuel consumption increased 4.66% by sweeping the water injection timing from the 150 CA to 50 CA before top dead center. However, the volumetric efficiency slightly ascended with increasing the water injection quantity and retarding the water injection timing. Finally, the NOx emissions declined with increasing the water injection quantity and retarding the water injection timing. However, CO emission and unburned HC emissions increased with increasing the water injection quantity and retarding the water injection timing. The main aim of this paper is expected to provide a comprehensively assessment of the thermo-physical of water on the thermodynamics, combustion, and emissions of the hydrogen enriched NGSI engine.     

Effects of steam injection on microturbine efficiency and performance

Microturbines offer new perspectives in small-scale heat and power production. Non-continuous heat demand however often leads to a reduced number of yearly running hours. This paper proposes an alternative by introducing water or steam injection without significantly increasing the overall cost. Steam injection (STIG^®) has been successful to boost performance and efficiency in industrial gas turbine cycles and similar effects are expected in the case of microturbines. Owing to the different way of controlling microturbines at non-constant shaftspeed, the response to steam or water injection differs from current STIG^® cycles. The purpose of this study was to examine the effects of steam injection on microturbine behavior by simulating its off-design characteristics in Aspen.     

Water and steam injection in micro gas turbine supplied by hydrogen enriched fuels: Numerical investigation and performance analysis

This paper investigates the energetic and environmental performance of micro gas turbine plant with two proposed concurrent improvements: the methane-based fuel enriched by hydrogen and the humidification of the plant cycle. The energetic and environmental benefits of both features are well-know, and the aim of this work is the analysis of their combined impact on the micro gas turbine operation. Despite enhancing fuel with H₂ involves significant advantages like greenhouse emission reduction and a better combustion in case of low LHV fuels, most of commercial micro gas turbine combustors are not able to burn fuels with high hydrogen content unless structurally modified. On the contrary, has been demonstrated that humidified gas turbines (i.e., gas turbines with water injection, humid air turbine (HAT) and steam injection gas turbine (STIG) cycles) improve the combustion stability as well as electric power delivered and plant efficiency. Hence, in order to investigate the feasibility of the concurrent two features, the first step of this work was the thermodynamic analysis of a micro gas turbine supplied by methane-based fuels enriched with H₂ up to 20%_vol, considering both dry and humidified cycles. Since a combustion anomaly was detected, i.e., flashback, in the CFD study on the combustion chamber, a steam injection in the combustor has been added in the plant layout with the aim of overcoming the anomaly, and its effect on the combustion process has been analyzed also raising the hydrogen content up to 30%_vol. The main outcome of this paper is the assessment of the feasibility of supplying the combustor of the proposed HGT-STIG micro gas turbine with a hydrogen enrichment up to 30%_vol, achieving a safe and regular combustion mainly owing to a steam injection mass flow equal up to 125% of fuel flow.     

Experimental study of inlet manifold water injection on combustion and emissions of an automotive direct injection Diesel engine

This paper describes an experimental study conducted on a modern high speed common-rail automotive Diesel engine in order to evaluate the effects on combustion and pollutant emissions of water injected as a fine mist in the inlet manifold.     

Research on the performance of water-injection twin screw compressor

Due to the development of the automotive fuel cell systems, the study on water-injection twin screw compressor has been aroused again. Twin screw compressors with water injection can be used to supply the clean compressed air for the Proton Exchange Membrane (PEM) fuel cell systems. In this research, a thermodynamic model of the working process of water-injection twin screw compressor was established based on the equations of conservation of mass and energy. The effects of internal leakage and air–water heat transfer were taken into account simultaneously in the present mathematical model. The experiments of the performance of a prototype compressor operating under various conditions were conducted to verify the model. The results show that the predictions of the model are in reasonable agreement with the experimental data.     

Effect of fuel injection timing and injection pressure on performance in a hydrogen direct injection engine

The in-cylinder hydrogen fuel injection method (diesel engine) induces air during the intake stroke and injects hydrogen gas directly into the cylinder during the compression stroke. Fundamentally, because hydrogen gas does not exist in the intake pipe, backfire, which is the most significant challenge to increasing the torque of the hydrogen port fuel injection engine, does not occur. In this study, using the gasoline fuel injector of a gasoline direct-injection engine for passenger vehicles, hydrogen fuel was injected at high pressures of 5 MPa and 7 MPa into the cylinder, and the effects of the fuel injection timing, including the injection pressure on the output performance and efficiency of the engine, were investigated. Strategies for maximizing engine output performance were analyzed.The fuel injection timing was retarded from before top dead center (BTDC) 350 crank angle degrees (CAD) toward top dead center (TDC). The minimum increase in the best torque ignition timing improved, and the efficiency and excess air ratio increased, resulting in an increase in torque and decrease in NO_x emissions. However, the retardation of the fuel injection timing is limited by an increase in the in-cylinder pressure. By increasing the fuel injection pressure, the torque performance can be improved by further retarding the fuel injection timing or increasing the fuel injection period. The maximum torque of 142.7 Nm is achieved when burning under rich conditions at the stoichiometric air-fuel ratio.     

Direct injection of hydrogen, oxygen and water in a novel two stroke engine

This short communication proposes novel two stroke engine burning hydrogen in oxygen in presence of large amounts of steam as residual gases. This engine has a bowl-in-piston combustion chamber, exhaust valves only and it uses direct injection of hydrogen, oxygen and water. Diesel-like compression ignition combustion is achieved by injecting the oxygen and the hydrogen in the surrounding steam close to a continuously operated glow plug. The operation of the engine is simulated by commercial softwares. The water injection enables acceptable metal temperatures and reduced heat losses. First computational results show brake efficiencies above 55% achieved with mass of water injected about twice the mass of oxygen and hydrogen mixture and operation with a significant amount of exhaust gas recirculation. It seems reasonable to guess efficiencies of the fully optimised and developed engine approaching the 60% mark, 20% higher than those of the state-of-the-art H₂ICEs designed for operation with air using the spark-ignition engine concept as well as of those projected for Diesel engines operating with exhaust energy recovery. Worth of mention is also the much higher power density following the two stroke operation.     

Optimization of operating conditions for compressor performance by means of neural network inverse

A way to optimize the parameters (i.e. operating conditions), related to compressor performance, based on artificial neural network and the Nelder–Mead simplex optimization method is proposed. It inverts the neural network to find the optimum parameter value under given conditions (artificial neural network inverse, ANNi). In order to do so, first an artificial neural network (ANN) was developed to predict: compressor pressure ratio, isentropic compressor efficiency, corrected speed, and finally corrected air mass flow rate. Input variables for this ANN include: ambient pressure, ambient temperature, wet bulb temperature, cooler temperature drop, filter pressure drop, outlet compressor temperature, outlet compressor pressure, gas turbine net power, exhaust gas temperature, and finally fuel flow mass rate. For the network, a feed-forward with one hidden layer, a Levenberg–Marquardt learning algorithm, a hyperbolic tangent sigmoid transfer-function and a linear transfer-function were used. The best fitting with the training database was obtained with 12 neurons in the hidden layer. For the validation of present database, simulation and experimental database were in good agreement (R²>0.99)$(R^2>0.99)$. Thus, the obtained ANN model can be used to predict the operating conditions when input parameters are well-known. Second, results from the ANNi that was developed also show good agreement with experimental and target data (error <0.1%), in this case, cooler temperature was found for a required efficiency. Therefore, the proposed methodology of ANNi can be applied to optimize the performance of the compressor with an elapsed time minor to 0.5 s.     

Evaluation and analysis of evaporation cooling on thermodynamic and pressure characteristics of intake air in a precooled turbine engine

The precooled turbine engine is applied to overcome the limitation of Mach number due to high temperature inlet air. This paper aims to investigate the effect of water injection cooling on the high-temperature intake air. Then, the theory evaluation and Eulerian-Lagrangian multiphase flow method are conducted to explore the thermodynamic process and resistance characteristics of the pre-cooling section built-in even spray apparatus with a drag reduction. Results show that larger amount of the injection flow rate at higher Mach number will deteriorate total pressure loss and flow field uniformity. Evaporation cooling can decrease flow loss by 9.4%–60.7%. Within 27 ms, total-temperature drop is in 14–144 K range with a low total-pressure drop coefficient of 0.56%–1.29%. Especially, mass flow will increase by 1.15%–18.50%. Thus, water injection cooling is conducive to a higher acceleration, as well as for improving the thermodynamics characteristics of inlet air for a turbine engine at a high Mach number.     

Effect of back-diffusion on the performance of an electrochemical hydrogen compressor

Hydrogen offers the potential to decarbonize the automotive and stationary power sectors and is therefore expected to play an increasingly significant role in meeting global energy demand. However, due to its low volumetric and gravimetric energy densities, it is important to find methods to efficiently store hydrogen in order to grow the hydrogen economy. Storing hydrogen as a compressed gas could be achieved by electrochemical compression (ECC), which is a membrane-based alternative to conventional mechanical compressors. ECC can be superior to mechanical compressors because of its higher efficiency, lack of moving parts and noiseless operation. Here, we report on the ECC of hydrogen using a Nafion 115 membrane at room temperature. Pressure vs. time curves have been collected at various operating voltages, and a compression ratio of 150 has been achieved with a single cell at an operating voltage of 0.1 V. This work focuses on the loss in electrochemical compression efficiency due to back-diffusion. A theoretical formulation for the ECC process incorporating back-diffusion is proposed and validated by experiments. A robust definition for ECC efficiency that properly accounts for back diffusion is also proposed.     

Effect of water injection and spark timing on the nitric oxide emission and combustion parameters of a hydrogen fuelled spark ignition engine

One of the main problems with hydrogen fuelled internal combustion engines is the high NO level due to rapid combustion. Use of diluents with the charge and retardation of the spark ignition timing can reduce NO levels in Hydrogen fuelled engines. In this work a single cylinder hydrogen fuelled engine was run at different equivalence ratios at full throttle. NO levels were found to rise after an equivalence ratio of 0.55, maximum value was about 7500 ppm. High reductions in NO emission were not possible without a significant drop in thermal efficiency with retarded spark ignition timings. Drastic drop in NO levels to even as low as 2490 ppm were seen with water injection. In spite of the reduction in heat release rate (HRR) no loss in brake thermal efficiency (BTE) was observed. There was no significant influence on combustion stability or HC levels.     

Blade cooling optimisation in humid-air and steam-injected gas turbines

Humidified gas turbine cycles such as the humidified air turbine (HAT) and the steam-injected gas turbine (STIG) present exciting new prospects for industrial gas turbine technology, potentially offering greatly increased work outputs and cycle efficiencies at moderate costs. The availability of humidified air or steam in such cycles also presents new opportunities in blade and disk cooling architecture. Here, the blade cooling optimisation of a HAT cycle and a STIG cycle is considered, first by optimising the choice of coolant bleeds for a reference cycle, then by a full parametric optimisation of the cycle to consider a range of optimised designs. It was found that the coolant demand reductions which can be achieved in the HAT cycle using humidified or post-aftercooled coolant are compromised by the increase in the required compression work. Furthermore, full parametric optimisation showed that higher water flow-rates were required to prevent boiling within the system. This corresponded to higher work outputs, but lower cycle efficiencies. When optimising the choice of coolant bleeds in the STIG cycle, it was found that bleeding steam for cooling purposes reduced the steam available for power augmentation and thus compromised work output, but that this could largely be overcome by reducing the steam superheat to give useful cycle efficiency gains.     

Improvement of engine performance with high compression ratio based on knock suppression using Miller cycle with boost pressure and split injection

In theory, high compression ratio has the potential to improve the thermal efficiency and promote the power output of the SI engine. However, the application of high compression ratio is substantially limited by the knock in practical working process. The objective of this work is to comprehensively investigate the application of high compression ratio on a gasoline engine based on the Miller cycle with boost pressure and split injection. In this work, the specific optimum strategies for CR10 and CR12 were experimentally investigated respectively on a single cylinder DISI engine. It was found that a high level of Miller cycle with a higher boost pressure could be used in CR12 to achieve an effective compression ratio similar to CR10, which could eliminate the knock limits at a high compression ratio and high load. To verify the advantages of the high compression ratio, the fuel economy and power performance of CR10 and CR12 were compared at full and partial loads. The result revealed that, compared with CR10, a similar power performance and a reduced fuel consumption of CR12 at full load could be achieved by using the strong Miller cycle and split injection. At partial load, the conditions of CR12 had very superior fuel economy and power performance compared to those of CR10.     

Particle emissions of direct injection internal combustion engine fed with a hydrogen-rich reformate

Thermochemical Recuperation is a promising waste heat recovery method that enables utilization of the engine waste heat together with onboard hydrogen production resulting in a significant improvement in thermal efficiency and a massive reduction in gaseous pollutants emission. However, an unexpectedly high particle emission level as compared to the gasoline-fed engine was measured despite the combustion of a hydrocarbon-free hydrogen-rich methanol steam reforming (MSR) products, containing 75% mol. H₂ and 25% mol. CO₂. In the existing literature, this phenomenon has not described yet.In this reported study, experiments are performed to investigate reasons of the elevated particle emissions by a direct injection spark ignition engine fed with MSR reformate, and results are compared with a baseline engine fed with gasoline at the same engine loads and speeds. Results of particle number concentration and size distribution measurements show that the total particle number concentration emission of engine fed with MSR reformate is 170% higher compared to gasoline. A direct experimental comparison between the port and the direct reformate injection performed on the same engine shows an increase in particles formation with a direct injection method. Based on these findings, several hypotheses are presented attributing to excessive lubricant involvement in the combustion process. The peculiarities specific for direct reformate injection that could result to the enhanced particles formation are jet – lubricated wall interaction, lubricant vapor entrainment into the reformate jet and shorter flame quenching distance of hydrogen compared to gasoline.     

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.