Temperature Of Injected Water Research Articles

Optimization Simulation of Different Injection and Production Parameters of Enhanced Geothermal Systems

Enhanced Geothermal System (EGS), as a key technology for the extraction and utilization of geothermal energy in deep strata and high temperature rock mass, has a broad application prospect in the field of energy. In order to understand the sustainable utilization capacity of the enhanced geothermal system, explore the influence law of different factors on the heat production capacity of geothermal Wells, and design a reasonable geothermal energy development and utilization program. The influence of different injection and production parameters on thermal recovery performance was studied by numerical simulation, and the main influencing factors were analyzed by orthogonal experiment. The results show that water injection rate has the greatest effect on the injection-production parameters, followed by well spacing and water injection temperature, and fracture opening and fracture number have the least effect. The optimal parameter combination is water injection rate of 10kg/s, well spacing 500m, water injection temperature 40℃, crack opening 0.09mm and crack number 60.

Numerical investigation of electricity generation potential by water circulating through three horizontal wells at Fengshun geothermal field in China

Fengshun geothermal field is the first medium and low temperature geothermal area in China, which is used for electricity generation. At present only vertical wells are employed to extract heat energy. After about 40 years of exploitation, the production temperature and rate are all declined. In this work, based on the hydrogeological data of the study area, the deep reservoir temperature and corresponding circulation depth of underground hot water are predicted with a silica thermometer. To fully develop the deep heat reservoir, we proposed a new heat exploitation scheme through three horizontal wells, computed the electricity generation potential and efficiency, and analyzed the main factors affecting heat production. The results indicate that under the reference conditions, the three horizontal well system attaches an electric power of 2.70–1.5 MW, a reservoir impedance of 0.13–0.27 MPa/(kg/s), a pump power of 0.29–1.16 MW, and energy efficiency of 7.34–1.30 during the reservoir lifetime of 43.6 years. Thus, this three-horizontal-well system has significant development potential in Fengshun deep geothermal reservoir. Sensitivity analysis indicates that water production rate, injection temperature and initial reservoir temperature have a significant impact on heat production performance. Reducing the water production rate and injection temperature within a certain range can improve energy efficiency. For the precise design of power generation systems and the accurate evaluation of production performance, field logging data is necessary.

Experimental research of direct water injection characteristics over wide range of injection temperature and ambient pressure

Direct water injection (DWI) within internal combustion engine has become a promising technology due to its potential for suppressing knock, reducing emissions and lowering fuel consumption. The spray morphology shows a significant impact on the effectiveness of DWI, which makes it of great research significance. In this research, the spray characteristics of water jet under different conditions were investigated based on a constant volume vessel. The water injection temperature ranged from 30 °C to 240 °C, and the ambient pressure varied from 0.2 bar to 10 bar. The results showed that the spray width at near-field increases with water temperature. However, at ambient pressures of 0.8 bar–2.5 bar, higher superheat level resulted in severe spray collapse, manifested as significantly reduced spray width. It was identified that the collapse under flash boiling occurs as a result of the presence of the low-pressure zone at the center of the spray, and higher superheat level migrate the low-pressure zone closer to the nozzle exit, resulting in enhanced spray collapse. This could lead to excessive water mist concentration in partial region, negatively affecting combustion process and potentially causing oil emulsion in actual engine operation. This work also suggests a strong correlation between spray collapse and water injection pressure, in addition to superheat level and ambient pressure. The findings of this work have the potential to provide effective reference for high-temperature water injection strategies in internal combustion engines.

Numerical simulation of electricity generation potential through five vertical wells at Fengshun geothermal field in China

Fengshun geothermal field is the first medium low temperature geothermal field to exploit geothermal energy for electricity generation in China. Due to poor economy and low efficiency, the geothermal power plant was forced to shut down in 2016. In this work, based on the geological data of the well ZK11, we proposed a new heat exploitation scheme with five vertical wells and a binary system, computed the power generation potential and efficiency, and analyzed the main factors influencing heat production. The results indicate that through the five vertical wells, the system attains an electrical power of 1.49–1.05 MW, a reservoir impedance of 0.23–0.29 MPa/(kg/s), a pump power of 0.30–0.49 MW, and an electrical energy efficiency of 4.55–2.12. The electric power of unit flow rate is 22.4–31.7 times that of the existing power plant. Thus, this five-vertical-well system has significant development potential for medium low temperature hydrothermal field. The sensitivity analysis indicates that overburden and underburden permeability, water production rate and injection temperature have a significant impact on heat production performance. Increasing the overburden or underburden permeability will significantly reduce reservoir impedance and increase energy efficiency. Reducing the water production rate and injection temperature within a certain range can improve energy efficiency. This work also provides a guideline for the exploitation and power generation of future medium low temperature hydrothermal field in Fengshun and other sites under similar conditions.

Heat and mass transfer analysis during the process of methane hydrate dissociation by thermal stimulation

Natural Gas Hydrate (NGH) is characterized by large reserves and cleanliness, which has attracted wide attention around the world. Thermal stimulation is considered to be one of the possible methods to facilitate hydrate dissociation. In this paper, the hydrate is dissociated through injecting hot water. In order to reveal the influence of the speed and the temperature of injected hot water on the temperature distribution, hydrate dissociation front, gas production rate, and cumulative gas production, a 2D cylindrical mathematical model of thermally-induced hydrate dissociation was established. The results show that the dissociation process can be regarded as a moving boundary ablation process. The dissociation front divides the whole reservoir into three sections: complete dissociation section, ongoing dissociation section, and undissociated section, and the range of ongoing dissociation section is a very narrow area characterized by a relatively intensive temperature contour, which indicates that the temperature drops rapidly during the hydrate dissociation. The temperature at the dissociation front is almost constant under different hot water injection speeds or temperatures. The injection speed and the temperature of hot water seem to have similar effects on hydrate dissociation. The enhanced hot water injection speed or hot water injection temperature will result in a faster gas production rate, a quicker movement of the dissociation front, and a shorter duration time of gas production, however, hot water injection speed and temperature have little impact on the final gas production. The results may provide a guidance for safely and efficiently exploiting NGH.

Heat Transfer Analysis of Enhanced Geothermal System Based on Heat-Fluid-Structure Coupling Model

Dry hot rock geothermal resources by virtue of its wide distribution, large reserves, clean and low-carbon, stable, high utilization rate, and other characteristics have been widely used. The enhanced geothermal system (EGS) is the most efficient approach for harnessing and exploiting geothermal energy from hot, arid rock formations. To investigate the impact of varying parameters on heat recovery in EGS operations, we employed the COMSOL numerical simulation software to construct a seepage heat transfer model for fractured rock masses. Essential parameters and boundary conditions were established, followed by conducting numerical simulations. Through the numerical simulation results, the temporal and spatial changes of coupling effects among seepage field, stress field, and temperature field in fractured rock mass were analyzed. We investigated the impact of water injection temperature, injection-production pressure difference, injection flow rate, and initial reservoir temperature on the heat transfer process. The findings indicate that raising the water injection temperature and injection-production pressure difference can enhance the reservoir’s heat recovery capability. However, it may also accelerate thermal breakthrough and reduce the system’s operational lifespan. The higher injection flow rate can improve the heat recovery efficiency. However, too large injection flow can cause problems in other aspects of the reservoir; increasing reservoir temperature leads to higher production temperatures, which can potentially result in dynamic catastrophes. Therefore, while ensuring the heat recovery efficiency of the system, the operation life of the system can be extended by adjusting the water injection temperature in stages, setting a reasonable injection and production pressure difference, and selecting an appropriate injection flow rate, so as to achieve the purpose of EGS optimization.

Long-term numerical investigation of Northern Gateway Heat Network

Considering climate change and countries’ measures towards greenhouse gas emissions (e.g., European energy and climate targets of achieving net-zero greenhouse gas emissions by 2050) [1], it is crucial to implement renewable energy sources and district-level heating and cooling systems. Many district-level heating and cooling systems have been established in Europe. However, just a limited number of them are renewable energy source based. One of the most efficient ways of heating and cooling supply is to use geothermal energy as it is renewable, sustainable, and environmentally friendly. Groundwater heat pumps (GWHPs) utilise low-temperature sources to provide heating and cooling to buildings, which makes them a highly efficient, environmentally friendly, and low-carbon technology suitable for both small and large-scale applications.
 Northern Gateway Heat Network project, which is a groundwater-based heat pump system aiming to provide heating and domestic hot water to around 300 dwellings, offices, and healthcare buildings, is considered as a case study in this research. It was designed to supply 75% of the total heating demand with an 800-kW output heat pump benefitting from the groundwater extracted from the depths between 135m and 200m at around 12.5°C. BH1, BH2 and BH3 are the injection wells, whilst BH4 and BH5 are the abstraction wells (see Figure 1) [2, 3].
 A 3D finite element modelling was carried out in FEFLOW [4] to investigate the thermally affected zone and the possibility of thermal feedback resulting from water injection temperature affecting abstraction temperature. The 3D modelling aims at investigating the impact of the system in the long term (100 years) and how to improve the system’s efficiency and sustainability by considering four different scenarios: (1) continuous space heating (12 months), (2) space heating (10 months) and recovery (2
 months), (3) space heating (10 months) and cooling (2 months) and (4) aquifer thermal energy storage (swap injection and abstraction wells in 2 months cooling period) (ATES).
 The results suggest that thermal feedback occurs after almost 60 years for the actual case (continuous space heating), which decreases the system’s efficiency. Figure 1 illustrates the thermal plume development after 100 years of space heating operation (cold water injection at 5°C). Although the spacing between the production and injection wells is around 530 m, the abstraction temperature was affected by the cold-water injection, and it decreased by almost 10% at the end of 100 years of simulation at BH4.
 The space heating and recovery, and space heating and cooling also witnessed a decrease in water extraction temperature at BH4. The injection temperature was set to 35°C for the space cooling period. Adding two months of recovery or two months of space cooling delayed the thermal feedback time by 17% and 8%. The results show that the system can supply two months of space cooling without a need for an additional supply from the heat pump. Furthermore, when two months of space cooling is added, the thermal energy gain increases by 20% compared to space heating-only operation. The ATES operation also increased the thermal energy gain by 173% thanks to the stored energy in the ground and higher volume of water extraction during the space cooling period. Table 1 shows the thermal energy gain from each well in each scenario, calculated considering the thermal feedback impact.
 This paper highlights the long-term numerical investigation of the Northern Gateway Heat Network, considering different scenarios, including continuous space heating, space heating and recovery, space heating and cooling, and ATES. It also discusses the thermal impact and thermal plume development in different scenarios and how the thermal plume affected the system efficiency due to thermal feedback. The results indicate that the GWHP system can provide direct space cooling, thereby significantly increasing the sustainability and efficiency of the system. Moreover, the application of the ATES system further improves the system’s sustainability and efficiency.

Numerical study on natural gas hydrate production by hot water injection combined with depressurization

The low efficiency and unstable gas production of hydrate exploitation have become the difficulties restricting the commercial development of combustible ice. In this work, based on the existing geological conditions, this paper establishes a low-permeability hydrate heterogeneous reservoir model to analyze the effects of hot water injection on well and reservoir. The results show that the greater the wasted heat from the produced water and some injected water migrating to the gaseous hydrocarbon layer and the underlying at the middle and late stage of hydrate production as the hot water injection rate. Moreover, the gas and water production will suddenly appear surge phenomenon during the hydrate production due to the disappearance of the water lock effect affected by thermal-hydraulic-chemical multi-field coupling, which depends on the hot fluid properties. Therefore, the new technology of slow hot water injection after depressurization or different injection rates at different stages in the injection well is proposed in this paper. And it is also necessary to optimize the vertical position of the injection well or add a thin layer with low permeability at the bottom of the gaseous hydrocarbon layer. Finally, the hot water injection temperature should be controlled above 50 °C.

Parametric analysis of water injection in an offshore well using a semi-transient thermal-structural model

This paper presents a parametric analysis of the influence of the recycled water injection temperature and flow rate on the pressure differences between the concentric annuli of an offshore injection well using a semi-transient, thermal-structural model. The model is validated against field data, showing average relative deviations from the pressures and temperatures measured at the permanent downhole gauge (PDG) of 5% and 3%, respectively. To enable a clear assessment of the contributions of the independent variables on the inter-annular pressure behavior and, consequently, on the risk of casing failure over a wide range of conditions, the numerical results are presented in terms of dimensionless quantities involving the casing strength. The results indicate a stronger influence of the injection temperature on the magnitude of the inter-annular pressure difference (one of the root causes of casing failure). In contrast, the flow rate controls the trapped fluid cooling rate and, therefore, the rate of pressure change inside the annuli. Finally, aiming at identifying injection conditions that mitigate the risk of casing failure, the modeling framework is employed to simulate intermittent (cyclic) injection scenarios with variable periods of sustained injection and interrupted flow. Using synthetic input data, different combinations of injection/shut-in intervals reduced the pressure difference between neighboring annuli by as much as 11.5%.

Modeling, performance enhancement, and the NOx emission reductions of the triple-pressure reheat water-recuperated air-cooled gas turbine combined cycle power plant using interstage compressor water injection and optimization

Interstage compressor water injection (ICWI) reduces the work of an air compressor, air temperature at its outlet, adiabatic flame temperature, and NOx emissions. When ICWI is introduced to combined cycles, it decreases the surge margin for the air compressor and increases the mass flow rates of the gas through the gas turbine (GT) and generated steam for the heat recovery steam generator and, therefore, power output. For the combined cycle with ICWI, air with two distinct characteristics (before and after ICWI) is used to cool the GT and mix with the expanded gas. In this paper, ICWI was introduced to the triple-pressure reheat air-cooled GT combined cycle. Detailed modeling was carried out for the processes of compression, ICWI, combustion, and GT expansion. Constraints were imposed on the amount of injected water and its temperature and pressure leading to a practical application of ICWI and a safe surge margin for the air compressor. The efficiency of the combined cycle with ICWI was optimized relative to the pressure of ICWI, injected water temperature, and relative humidity of air at the outlet of the water injector at different values of turbine inlet temperatures and air compression ratios. The results indicated that ICWI and optimization could reduce the initial NOx emissions by more than 90% (the NOx emissions that are produced at the adiabatic flame temperature) and enhance cycle efficiency by 1.9 to 2.7 percentage points and power output by 27 to 34 percent. The water recovery system could produce a significant amount of water that exceeds twice the injected amount at no fuel cost and could be integrated into the cycle at no additional equipment costs if CO2 capture or exhaust gas recirculation was implemented.

An Algorithm to Optimize Water Injection Temperature for Thermal Recovery of High Pour Point Oil

With the advancement of conventional water displacement technology, cold damage may affect the vicinity of high pour point oil wells to a certain extent. Thus, the optimization of thermal recovery parameters of high pour point oil is of great significance to the oil field. In this study, a comprehensive model of the temperature distribution of the wellbore fluid was constructed, and the function of f(tD) was introduced to participate in the calculation of the thermal resistance of the formation. The temperature distribution along the wellbore was calculated and simulated under different conditions. The results show that the surface water injection temperature of 60.8℃ could ensure the desired water temperature reaching the target layer, and the injection temperature of 60.4°C could meet the needs of efficient development after considering the design of the 750-m insulated tubing. The final thermal recovery parameter optimization system could provide a theoretical reference for the thermal recovery design of the same type of reservoir.

A novel approach of water injection optimization applied in gasoline engines: An investigation on heated water injection

Water injection technique is a promising solution for accurate combustion control, but oil emulsion obstacle its commercial application. The present study proposes a practical approach for optimizing water spray atomization and evaporation, in which water is heated through exhaust gas recovery and directly injected into combustion chamber with a flash boiling. Firstly, a heated water injection (HWI) system was designed and established. Then, experiments were conducted to explore the effects of HWI parameters on engine combustion and emissions characteristics in terms of water injection strategies. The results present that HWI increase water evaporation rate and improves combustion efficiency. The HWI lowers flame propagation speed and improves specific heat ratio of air–fuel mixture. Elevated injection temperature lowers duration of flame kernel formation, which shortens ignition delay prolonged under conventional water injection. CA10 is advanced 4.5°CA under same spark advance while compared to conventional water injection. Moreover, HWI can not only reduce production of NOX and CO emissions but also effectively lower HC emissions by 26.2%, as water injection temperature increased to 205℃. However, excessive water injection mass and inappropriate water injection timing may worsen ignition and flame propagation, increasing unburned loss and misfire probability. The present results provide considerable evidence for the application of HWI within modern gasoline engines.

An investigation into the effect of water injection parameters on synergetic mining of geothermal energy in mines

Cooling energy demands are high and increase with the mining depths in conventional mine cooling systems, which account for the most of the total energy consumption. The synergetic mining of mine geothermal energy (SMGE) is a subversive and promising approach for heat hazard control of deep mines with the advantage of low energy consumption and low cost. In this study, the similarity criteria for the similar simulation of SMGE are deduced by the equation analysis method, and the similarity criteria number between the full-scale model and the reduced-scale model is determined. Based on the geometric scale ratio of 1:100, a simulation experiment system including ventilation system and geothermal exploitation system is established. In addition, the influence of water injection parameters on cooling effect of roadway and heat recovery performance of the SMGE system is investigated. The results indicate that the temperature of surrounding rock is cooled gradually during the water injection and heat recovery in rock formation, which reduces the temperature increase rate of airflow in the roadway. When the injection water temperature is reduced from 28 °C to 11.5 °C, the cooling rate of roadway can be observable increased, but it results in a faster temperature decrease in production water with time. Increasing the water injection time from 35 min to 65 min will give rise to the temperature reduction degree of surrounding rock and decrease to the temperature increase rate of airflow in roadway. And the time of water injection is directly proportional to the water production flow rate in production well, but inversely proportional to the temperature in production water. A high injection rate facilitates the cooling rate of the roadway and increases the range of heat recovery in formation, but a small flow rate can achieve a better ultimately cooling effect under the same total water injection volume. Decreasing the water injection rate from 1.6 L/min to 0.6 L/min will increase the time of stable production flow and the rate of reduce in water temperature in the production well. Furthermore, changes in the level of the injection well position will result in different injected water seepage characteristics, which affects the cooling effect of roadway and heat recovery performance of the SMGE system simultaneously.

COUPLING A GEOMECHANICAL RESERVOIR AND FRACTURING SIMULATOR WITH A WELLBORE MODEL FOR HORIZONTAL INJECTION WELLS

Reservoir cooling during waterflooding or waste-water injection results in thermo-poro-elastic stresses that can significantly alter the reservoir stress tensor field. In addition, colloidal particles in the injected water can filter on the borehole and fracture surfaces resulting in matrix permeability reduction. Fractures are likely to initiate and propagate from injectors because of these thermal and filtration effects. These fractures are of great concern for both environmental reasons and their strong influence on reservoir sweep and oil recovery. In this paper, a fully coupled reservoir-fracture-wellbore model was developed. Fluid flow, solid mechanics, energy balance, fracture initiation and propagation, and particle filtration are modeled in the reservoir, fracture, and wellbore domains. The coupled non-linear systems of equations are solved implicitly using the Newton-Raphson method. Simulation results show that water quality and thermal effects control fluid leak-off and fracture growth. While it is difficult to predict the exact location of fracture initiation due to reservoir heterogeneity, we propose a reasonable method to handle fracture initiation and growth without a predefined fracture location. In open-hole completions, "thief" fractures may propagate deep into the reservoir. Thermal stress changes in the injection zone are shown to be significant because of the combined effects of forced convection, heat conduction, and poro-elasticity. Accurate predictions of thermal stress in different reservoir layers allow us to conduct numerical studies on fracture height growth and containment. We show that controlling the injection water temperature and the water quality are an effective way to ensure fracture containment.

Investigation of Water Composition on Formation Damage and Related Energy Recovery from Geothermal Reservoirs: Geochemical and Geomechanics Insights

The main challenge in extracting geothermal energy is to overcome issues relating to geothermal reservoirs such as the formation damage and formation fracturing. The objective of this study is to develop an integrated framework that considers the geochemical and geomechanics aspects of a reservoir and characterizes various formation damages such as impairment of formation porosity and permeability, hydraulic fracturing, lowering of formation breakdown pressure, and the associated heat recovery. In this research study, various shallow, deep and high temperature geothermal reservoirs with different formation water compositions were simulated to predict the severity/challenges during water injection in hot geothermal reservoirs. The developed model solves various geochemical reactions and processes that take place during water injection in geothermal reservoirs. The results obtained were then used to investigate the geomechanics aspect of cold-water injection. Our findings presented that the formation temperature, injected water temperature, the concentration of sulfate in the injected water, and its dilution have a noticeable impact on rock dissolution and precipitation. In addition, anhydrite precipitation has a controlling effect on permeability impairment in the investigated case study. It was observed that the dilution of water could decrease formation of scale while the injection of sulfate rich water could intensify scale precipitation. Thus, the reservoir permeability could decrease to a critical level, where the production of hot water reduces and the generation of geothermal energy no longer remains economical. It evident that injection of incompatible water would decrease the formation porosity. Thus, the geomechanics investigation was performed to determine the effect of porosity decrease. It was found that for the 50% porosity reduction case, the initial formation breakdown pressure reduced from 2588 psi to 2586 psi, and for the 75% porosity reduction case it decreased to 2584 psi. Thus, geochemical based formation damage is significant but geomechanics based formation fracturing is insignificant in the selected case study. We propose that water composition should be designed to minimize damage and that high water injection pressures in shallow reservoirs should be avoided.

Effect of direct water injection temperature on combustion process and thermal efficiency within compression ignition internal combustion Rankine engine

Compression ignition-internal combustion Rankine cycle (CI-ICRC) concept implement oxy-fuel combustion, direct water injection (DWI) and waster heat recovery into traditional diesel cycle to realize ultra-high thermal efficiency and low emission powertrain. As indicated by ICRC concept, the DWI process show critical impact on its combustion process and thermal efficiency. This paper dedicated in investigating the effect of different DWI temperature on cycle performance and thermal efficiency within prototype CI-ICRC engine, in order to do so, independent DWI system, O2/CO2 intake system and reconfigurable electronic controller is established. Combustion characteristics including in-cylinder pressure, heat release rate, combustion stability, brake thermal efficiency are experimentally investigated. The cycle performance and thermal efficiency are proved to be optimized under elevated DWI temperature, an optimum 46.6% brake thermal efficiency is achieved, while the coefficient of variation remains around 1%. The NOX and soot emissions are both reduced under DWI utilization, the mechanism of soot reduction is highly related to thermolysis of water or carbon-water reactions which further chemical kinetic analysis is needed. The result of this study provides fundamental information for future CI-ICRC engine optimization, and can also be utilized in providing reference guidance for DWI implementation within modern internal combustion engines.

Effect of direct water injection on combustion and emissions characteristics of marine diesel engines

In this study, the effect of direct water injection (DWI) was investigated on the performance of marine diesel engine based on the three-dimensional simulation model. The water injection quantity, temperature and timing were researched on the in-cylinder pressure and temperature, indicated power and NOx emissions. Then, the DWI strategies were compared with the exhaust gas recirculation (EGR). The results showed that the in-cylinder pressure, temperature, indicated power and NOx emissions decrease with increasing of water quantity. Reductions in NOx emissions up to 55.6% were obtained after applying DWI to the engine at the compression stroke. The water injection temperature has a little effect on the combustion and emissions of marine engine. The indicated power decreased when the water injection timing in the compression stroke. However, the indicated power increased when the water injection timing in the late combustion phase. The water injection timing in the compression stroke has more potential in reduction NOx emissions. The NOx emissions with water injection in the compression stroke decreased by 40% compared to the value with water injection in the later combustion phase. The ability of DWI and EGR were researched on the solve the trade-off between power and NOx emissions. The results showed that the DWI strategy can reduce NOx emissions at the higher indicated power compared with the results of EGR.

Mechanical Analysis and Application of Multi-packer Tubing String in Layered Water Injection in Dagang Oilfield

In Zaoyuan Oilfield and Wangguantun Oilfield of Dagang Oilfield Company, the wells feature large depth, high temperature, high water injection pressure, serious corrosion and scaling and complex wellbore conditions. The existing mechanical analysis software for tubing string in layered water injection is only capable of analyzing the axial force and axial deformation and checking the safety of strength under the lowering and lifting working conditions. Therefore, a mechanical analysis method for the multi-packer tubing string has been derived by comprehensively considering the constraint and impact of anchor tools and packers on tubing string deformation, the well deviation and orientation, the statical indeterminacy of the multi-packer tubing string as well as the impact of injected water temperature and expansion effect by injection pressure. The method is capable of analysis on the axial force, deformation and stress strength of each string segment of the layered water injection tubing string with two or more packers, and helps improve the accuracy of mechanical analysis of tubing string under different well conditions and working conditions. Case analysis shows that the analysis results can be used to guide the design of tubing string for layered water injection as well as to guide the research and development of auxiliary downhole tools such as layered water injection packers and anchor tools.

Effects of Water Injection Strategies on Oxy-Fuel Combustion Characteristics of a Dual-Injection Spark Ignition Engine

Currently, global warming has been a serious issue, which is closely related to anthropogenic emission of Greenhouse Gas (GHG) in the atmosphere, particularly Carbon Dioxide (CO2). To help achieve carbon neutrality by decreasing CO2 emissions, Oxy-Fuel Combustion (OFC) technology is becoming a hot topic in recent years. However, few findings have been reported about the implementation of OFC in dual-injection Spark Ignition (SI) engines. This work numerically explores the effects of Water Injection (WI) strategies on OFC characteristics in a practical dual-injection engine, including GDI (only using GDI), P50-G50 (50% PFI and 50% GDI) and PFI (only using PFI). The findings will help build a conceptual and theoretical foundation for the implementation of OFC technology in dual-injection SI engines, as well as exploring a solution to increase engine efficiency. The results show that compared to Conventional Air Combustion (CAC), there is a significant increase in BSFC under OFC. Ignition delay (θF) is significantly prolonged, and the spark timing is obviously advanced. Combustion duration (θC) of PFI is a bit shorter than that of GDI and P50-G50. There is a small benefit to BSFC under a low water-fuel mass ratio (Rwf). However, with the further increase of Rwf from 0.2 to 0.9, there is an increment of 4.29%, 3.6% and 3.77% in BSFC for GDI, P50-G50 and PFI, respectively. As WI timing (tWI) postpones to around −30 °CA under the conditions of Rwf ≥ 0.8, BSFC has a sharp decrease of more than 6 g/kWh, and this decline is more evident under GDI injection strategy. The variation of maximum cylinder pressure (Pmax) and combustion phasing is less affected by WI temperature (TWI) compared to the effects of Rwf or tWI. BSFC just has a small decline with the increase of TWI from 298 K to 368 K regardless of the injection strategy. Consequently, appropriate WI strategies are beneficial to OFC combustion in a dual-injection SI engine, but the benefit in fuel economy is limited.

Experimental Analysis of Water Pressure and Temperature Influence on Atomization and Evolution of a Port Water Injection Spray

Port water injection (PWI) is considered one of the most promising technologies to actively control the increased knock tendency of modern gasoline direct injection (GDI) engines, which are rapidly evolving with the adoption of high compression ratios and increased brake mean effective pressure levels in the effort to improve their thermal efficiency. For PWI technology, appropriately matching the spray evolution and the intake system design along with obtaining a high spray atomization quality, are crucial tasks for promoting water evaporation so as to effectively cool down the air charge with moderate water consumption and lubricant dilution drawbacks. In the present paper, a detailed experimental analysis of a low-pressure water spray is presented, covering a lack of experimental data on automotive PWI systems. Phase doppler anemometry and fast-shutter spray imaging allowed us to investigate the influence exerted by the injection pressure level and by the water temperature on spray drop size and global shape, obtaining a complete database to be used for the optimization of PWI systems. The obtained results evidence how significant benefits in terms of atomization quality can be obtained by adopting injection pressure and water temperature levels compliant with standard low injection pressure technologies.