Main Injection Research Articles

Exergy analysis of a diesel methanol dual fuel engine with different regulatory strategies for meeting China VI emission regulations

To reveal the mechanism for high brake thermal efficiency (BTE) of diesel methanol dual fuel (DMDF) engine meeting China VI emission regulations without urea, experimental and computational methods were used to study the exergy distribution with different regulatory strategies. As the methanol energy ratio (MER) increased, the incomplete combustion exergy loss increased from 0.3 % to 5.5 %, while the exhaust exergy loss and heat transfer exergy loss decreased slightly. As the HP-EGR increased from 3 % to 23 %, exergy losses of incomplete combustion and exhaust decreased, resulting in a reduction in the engine exergy losses. As the LP-EGR increased from 3 % to 21 %, the exergy losses of heat transfer and incomplete combustion slightly decreased. By advancing the main injection timing, the decrease in exhaust flow rate and temperature led to a decrease in exhaust exergy loss and the combustion efficiency was improved from 95.0 % to 96.5 %. Both of them resulted in the highest exergy efficiency of 35.2 % at 12°CA BTDC. Finally, the exergy distributions of DMDF and diesel modes were compared at high and low loads. The research results can provide theoretical basis and engineering practical value for the development and optimization of DMDF engines from the perspective of exergy.

Emission control in a dual fuel low temperature combustion engine at intermediate loads

Intermediate to high load operation in dual fuel reactivity controlled compression ignition (RCCI) techniques is restricted due to uncontrolled combustion that causes engine knocking. Dual fuel strategies with advanced pilot injection and near-top dead center (TDC) main injection timings are reported to enhance combustion control, albeit with increased soot emissions, reduction of thermal efficiency, and emergence of an intricate trade-off between total hydrocarbon (THC) and oxides of nitrogen (NOx) emissions. In order to address these conflicting issues, an intermediate engine load, corresponding to 6 bar gross indicated mean effective pressure at 1500 and 2200 rev/min engine speeds was investigated in this work. The main objectives of this work are (1) to obtain combination of control parameters to achieve near-zero engine-out NOx and soot emissions and high thermal efficiency while minimizing THC and CO emissions; (2) to understand the effectiveness of diesel oxidation catalysts (DOCs) for the oxidation and reduction of exhaust gas species in the dual fuel mode; and (3) to understand the oxidation characteristics of the soot generated from the dual fuel mode. Optimum dual fuel low temperature combustion strategies, in terms of diesel injection timings, quantity and exhaust gas recirculation levels, were identified using the statistical multi response signal to noise (MRSN) ratio method in which NOx, soot and indicated efficiency were response variables. The performance of commercial DOCs, with different precious metal (Pt and/or Pd) loadings, were also studied at optimum dual fuel strategies for gasoline-diesel dual fuel operations. High DOC outlet temperatures (>∼340°C), due to the exotherm generated by the oxidation of high concentrations of THC and carbon monoxide (CO) emissions from dual fuel operations, resulted in greater than 90% THC conversion efficiency. The exotherm decreased the nitric oxide (NO) oxidation whereas the nitrogen dioxide (NO2) reduction reactions were favored over the DOC in the dual fuel mode at the intermediate load operating condition. Thermogravimetric analysis of the soot showed higher activation energy (177.2 kJ/mol), formed at the dual fuel optimum condition, relative to the activation energy (162.7 kJ/mol) of the soot formed in conventional diesel combustion (CDC).

Research on improving permeability of granite reservoir: Polyhydrogen chelating acid acidizing

ABSTRACT Acidization is a highly effective technique for increasing oil well productivity. Therefore, it is critical to study effective stimulation of low-permeability granite reservoirs using acidification. Using the granite reservoir of Baobab oilfield in Chad as the research object, the properties of reservoir rocks were tested using XRD and rock thin section analysis. Dissolution experiments, core flooding experiments, and CT scanning were used to investigate the increased permeability and changes in the pore structure of the cores during acidification. The minerals in the rocks are primarily plagioclase, kalifeldspar, and quartz, with trace amounts of calcite, chlorite, magnetite, illite, biotite, hornblende, sphene, and sericite. At 80°C and 10 mL of main acid injection, polyhydrogen chelating acid (6% HCl + 5% SA601 + 7% SA701) improved granite permeability more than mud acid (8% HCl + 2% HF) and fluoroboric acid (8% HCl + 8% HBF4), with permeability increase of 3.68. The CT three-dimensional images of the rocks show that both the cores acidified with polyhydrogen chelating acid and mud acid formed continuous acid-etched wormholes, while the cores acidified with fluoroboric acid did not. Compared to the mud acid, the core acidified by the polyhydrogen chelating acid produced more visible acid-etched wormholes. Meanwhile, the polyhydrogen chelating acid was more effective at improving the pore throats and expanding the flow channels in the core. This study serves as a reference for the application of acidification and increasing production in low-permeability granite reservoirs.

Investigation of the GCI main injection: experimental-numerical analysis of gasoline spray impact at reference engine conditions

This work deals with the experimental and numerical investigation of ultra-high pressure gasoline injection against heated walls in order to characterize the fuel evaporation and distribution in gasoline compression ignition combustion chambers. Spray-wall impingement tests have been conducted in a quiescent vessel and recorded by means of the Mie scattering technique. The test conditions have been set in line with those of a reference benched GCI engine, leading to 500 bar and 700 bar for the injection pressure, 298 K, 423 K, 493 K for the wall temperature, 20 mm and 30 mm for the injector-wall distance. The same test matrix has been reproduced by means of CFD three-dimensional simulations using a proper setting of the wall-impingement model and the joint use of CFD-FEM approaches for the vapour-wall heat exchange. The time evolution of the rebound spray has been recorded and then postprocessed leading to the width and the thickness of the cloud. The CFD results are in line with the experimental ones both in terms of the overall time evolution and punctual values, proving a good accuracy of the simulation in predicting the rebound/adhered fuel mass split and the local distribution of the fuel after the impingement. Given the reliability of the simulations, insights on the numerical wall film mass and evaporated mass have been provided in order to clarify the effect of increasing pressure, temperature, and distance.

Multi-objective Optimization of Diesel Engine Operating Parameters Under Highway Drive Conditions

Abstract Experimental and optimization work is carried out to study the effects of fuel injection pressure, boost pressure, pilot injection timing, pilot injection quantity and main injection timing as input parameters. A four-cylinder, automotive model direct injection diesel engine, incorporated with a variable-geometry turbocharger, was chosen for the experiment. Engine test runs are conducted at a driving condition of 80.3 Nm torque and an engine speed of 1750 rpm, respectively, corresponding to highway driving conditions, using 10 % of exhaust gases recirculated. The Response Surface Methodology is employed to design experiments and analyze the experimental data to optimize engine parameters, considering the mentioned parameters as input parameters. A multi-objective response approach is adopted to optimize engine-operating parameters to obtain desired performance and engine-out emissions. Confirmatory tests are conducted at design conditions to validate the results predicted by the model. It is observed that for the chosen engine configuration, the optimum performance and emission characteristics could be obtained with 120 kPa boost pressure, 61.1 MPa fuel injection pressure, and 11.5 % of total fuel amount as pilot injection and remaining as main injection quantity at 332° and 359° crank angle, respectively. Overall. fairly better engine performance was observed with the use of selected ranges. It is noted that with the procedures adopted, improved engine performance and a significant reduction in harmful emissions are obtained without using major add-ons. The investigation revealed excellent potential for a diesel engine to be an effective prime mover.

Computational investigation of a methanol compression ignition engine assisted by a glow plug

This work explores the feasibility of pure methanol combustion in a light-duty diesel engine assisted by a glow plug (GP). The simulations represented a mild engine load with an indicated mean effective pressure of 7 bar. An extensive computational study was conducted, and the successful operation of the pure methanol compression ignition engine was demonstrated. The effects of the GP position, spray umbrella angle, the relative angle (RA) between the glow plug and jet trajectory, and the injection strategy on the engine performance were evaluated. The autoignition of methanol-air mixture was found to primarily occur at an equivalence ratio between 0.2 and 0.4. However, an even richer mixture accompanied the lower temperature due to intense heat absorption of evaporation, significantly prolonging the ignition delay. Therefore, to improve the ignition and combustion heat release processes, RA was optimized to adequately control the mixture distribution around the GP. At each position of the GP, the optimum RA differed due to the complex flow and air-fuel mixing within the combustion chamber, which became smaller (from 12.5° to 5°) when the GP was moved anticlockwise from the intake port to the exhaust port regions. Furthermore, a split injection strategy was proposed to ensure the successful ignition of the methanol jets. The engine performance exhibited a high sensitivity to the pilot and main injection timings. A small pilot mass fraction of no higher than 20% was recommended to mitigate fuel jet-GP interaction and fuel impingement in the squish region.

Enhancing the usability range of acetylene in CI engines through split injection of high-reactive fuel under RCCI operation: Optimized operability using an MCDM approach

Reactivity Controlled Compression Ignition (RCCI) has emerged as a promising solution to address the challenges of advanced combustion techniques in diesel engines, balancing combustion control and emission reduction. This study investigates the impact of split-injection high-reactivity fuel (HRF) dosing in RCCI to enhance charge homogeneity at lower injection timing advancements. It systematically explores progressive advancements in HRF injection timing, distinguishing between main and pilot injections. The main injection varied from 20° bTDC to 70° bTDC, while the pilot injection, relative to the main injection, spans 25°-40° CA ahead with a 5° progression. As an LRF, Port-injected Acetylene supplements the process with variable premixed ratios. Further, using a multi-criteria decision-making method (AHP), the study optimizes operating conditions, proposing a main injection at 20° bTDC, a pilot injection 40° CA ahead, and 70 % LRF participation. This optimized condition yields significant benefits such as 32.99 % higher brake thermal efficiency (BTE), 160 % longer premixed duration, 18.65 % lower maximum temperature, 89.41 % lower NO emissions, 91.83 % lower hydrocarbon (HC) emissions, 91.24 % lower CO emissions and 97.20 % lower smoke opacity compared to conventional diesel combustion (CDC) operation. The results highlight the advantages of multiple fuel injections in RCCI, improving blending characteristics at lower injection angles.

Study on precise fuel injection under multiple injections of high pressure common rail system based on deep learning

The fluctuation of fuel injection quantity under multiple injections of high pressure common rail system leads to a decline in engine economy and emission performance, the precise injection control is the key problem in current research. In this study, a deep learning data-driven model of injection quantity under multiple injections was established based on generalized regression neural network (GRNN), and the particle swarm optimization (PSO) was introduced to optimize the smoothing factor in the model, thereby improving its prediction accuracy. An injection quantity correction method based on the data-driven model was proposed and applied to actual common rail fuel injection system for experimental verification. The results demonstrate that the proposed data-driven model has excellent prediction performance and generalization ability for the predicted main injection quantity with mean absolute percentage error of 1.10 % and determination coefficient of 0.997. Through the experimental verification of the correction method under 144 groups of operating conditions, it was observed that the maximum deviation of main injection quantity decreased from −25.83～17.91 mm3 to −9.81～7.64 mm3, and the maximum absolute deviation reduced by 62.02 %. The precise of injection control under multiple injections is improved.

Effects of diesel injector nozzle angle and split diesel injection strategy on combustion and emission characteristics of an ammonia/diesel dual-fuel engine

Pre-injection can effectively improve combustion and thermal efficiency while reducing unburned ammonia (uNH3) and N2O emissions in ammonia/diesel dual-fuel engines. Nevertheless, the pre-injected diesel often impacts the cylinder liner or piston pinch area, adversely affecting combustion and emissions. In this study, various narrow injector nozzle angles (90°/60°) of diesel fuel are applied on investigating engine performance and emissions. Experiments are conducted at 1200 r/min, IMEP 1.2 MPa, and AEF (ammonia energy fraction) 50 %, consisting of varying INA (injector nozzle angle) of 145°/90°/60°, PIR (pre-injection ratio) from 20 %–80 %, PIT (pre-injection timing) from −70 °CA ATDC to −30 °CA ATDC, and sweeping MIT (main injection timing). Results show that larger INA prefer a lower PIR and delayed PIT to reduce the pre-injected fuel hitting the liner, and smaller INA prefer a higher PIR to reduce the main-injected fuel hitting the piston wall. ITE of INA145° peaks at a moderate PIR and delayed PIT while ITE of INA90° and INA60° peaks at a high PIR and early PIT. Decreasing INA combined with high PIR and early PIT helps to reduce uNH3, N2O, and GHG emissions, at the cost of a slight decrease in ITE.

Optimization of NOX emissions of a CRDI DIESEL engine using CMA-ES method

Engine calibration is the tuning of embedded parameters in the engine control unit (ECU) software to improve vehicle characteristics and meet legal requirements. Due to the stricter emission limits and rising customer expectations, current ECU software may include variables up to 30,000, which require very much time for engine calibration development. For this reason, automotive manufacturers continuously develop mathematical-based optimization methods to find optimum operating conditions for the engines. This study aimed to develop an online optimization algorithm to conduct automated dynamometer tests in the calibration development process. A modified covariance matrix adaptation (CMA) algorithm, which is an evolutionary strategy (ES) method belonging to meta-heuristic optimization, was integrated with an automation system for online calibration optimization. Some CMA method parameters such as step size and damping factor were initially revised to achieve the method to function efficiently in online engine calibration. Optimization was conducted at three different operating points of a 2-liter common rail direct injection (CRDI) diesel engine, where NOx emission mainly impacts the New European Driving Cycle (NEDC) results. The main injection timing, rail pressure, pilot injection quantity and timing, manifold pressure, and mass air flow were controlled in the optimization process. Optimization targets were determined according to the NOx-PM Pareto curve for each operating point. Covariance matrix adaptation was used to generate Pareto curves. Sixty-five measurements were taken for each operating point in the optimization process. Once optimization targets were determined, optimization occurred at each operating point. A total NOx emission reduction of 3.8% was obtained in the NEDC test, while fuel consumption and PM remained almost the same at steady-state operating points. The modified CMA-ES algorithm is expected to be an efficient method for online calibration optimization.

Split injection timing optimization in ammonia/biodiesel powered by RCCI engine

Employing carbon-neutral (NH3) and low carbon footprint (biodiesel) fuels in Reactivity Controlled Compression Ignition (RCCI) engine mode is one possible method for minimizing carbon emissions in diesel engines. In this study, a Compression Ignition (CI) engine was customized to run in RCCI mode, employing High Reactive Fuel (HRF) as biodiesel and Low Reactive Fuel (LRF) as ammonia (NH3). Based on our earlier findings, the proportion of ammonia in premixing is fixed at 40 %. In the first phase, the primary injection timing of the algal biodiesel varied between 12 and 21°CA bTDC at a preset pre-injection timing of 46°CA bTDC. In the next phase, the pre-injection time varied between 46 and 54°CA bTDC, with the optimal main injection time being 18°CA. The result suggested that the optimal main and pre-injection at 18 and 58°CA bTDC increased the Cylinder Pressure (CP) by 30.1 %, and peak HRR and combustion phase angle were advanced. Brake Thermal Efficiency exhibited an 11 % enhancement, with Brake Specific Energy Consumption decreasing by 24.1 %. Nitrogen Oxide levels saw an increase of around 39.5 %. In contrast, reductions of 19.2 %, 23.5 %, 39.7 %, and 21.7 % were observed in Hydrocarbons, Carbon Monoxide, smoke emissions, and Exhaust Gas Temperature, respectively, compared to the single injection under full load conditions.

Investigation of Split Diesel Injections in Methanol/Diesel Dual-Fuel Combustion in an Optical Engine

Methanol is a promising alternative fuel due to its wide availability of raw materials, mature production processes, and low production cost. However, because of the low cetane number, methanol must include a more reactive fuel to assist with combustion when used in compression ignition (CI) engines. In this study, based on the optical CI engine platform, methanol is injected into the intake port, and diesel is directly injected into the cylinder to achieve dual-fuel combustion. The effects of the methanol energy ratios and diesel split injection strategies on combustion are investigated. The results show that the premixed blue flame was mainly concentrated in the near wall region, whereas the yellow flame produced by diesel combustion tended to concentrate in the central region as the methanol energy ratio increased. When the methanol energy ratio exceeded 50%, the ignition delay was significantly prolonged, while the flame area was greatly reduced. Meanwhile, the peak values for the cylinder pressure and heat release rate decreased significantly, indicating a significant deterioration in combustion. At the earlier diesel pre-injection timing at −58°, the overall dual-fuel combustion at each main injection timing exhibited low-temperature premixed combustion characteristics, with a lower peak exothermic rate and flame brightness. At the later pre-injection timing at −33°, the spray flame at all main injection timings could be observed, with higher peak heat release rates and indications of thermal efficiency. Combustion at later main injection timings was characterized by diffusion combustion, and the main injection timing could effectively regulate the combustion process through phase adjustment.

Diesel direct injection and EGR optimization for a syngas-diesel dual-fuel generator operating at constant load

Diesel generators are widely used to produce electricity and heat in remote communities. However, their use contributes to harmful pollutant and greenhouse gas (GHG) emissions, negatively impacting the environment and public health. Syngas, which is a sustainable fuel, can play an important role in the transition from petroleum to renewable fuels. When used in dual-fuel diesel engines, it can contribute to reducing GHG emissions and the cost of transporting diesel, especially for rural and remote communities. This study investigates the effects of optimizing the diesel direct injection (DI) and exhaust gas recirculation (EGR) strategies on the combustion and emission performance of a syngas-diesel dual-fuel generator at constant load. The experiments were conducted using a 30-kW generator with a four-stroke, four-cylinder, turbocharged, and electronically controlled direct-injection diesel engine. The intake manifold of the engine was modified to allow introducing syngas upstream of the turbocharger. The syngas was simulated using individually controlled flow rates of hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), and nitrogen (N2). The syngas flow rate was adjusted to replace 40% of the energy provided by diesel fuel while optimizing the diesel DI parameters such as the pilot injection timing, main injection timing and diesel direct injection rail pressure, as well as the EGR rate. The findings of this study reveal that optimizing diesel injection strategy and appropriately raising the EGR rate have a positive impact on the engine performance and emissions.

Research on Abnormal Starting Noise of Efficient Engine Caused by Abnormal Combustion Noise

Article Research on Abnormal Starting Noise of Efficient Engine Caused by Abnormal Combustion Noise Feng Huang 1, * , Xiaochun Zeng 1, Xili Wang 1, Xinqi Qiao 2, Yi Wang 1, Liang Fang 3, Yunhua Zhang 3, Dengcheng Liu 4, and Yonghong Deng 4 1 Jiangling Motors Co., Ltd., Nanchang 330001, China 2 Mechanical and Power Engineering College, Shanghai Jiao Tong University, Shanghai 200092, China 3 Automobile College, Tongji University, Shanghai 200092, China 4 Nanchang Automotive Institute of Intelligence & New Energy, Nanchang 330052, China * Correspondence: fhuang6@jmc.com.cn Received: 20 February 2024; Revised: 7 April 2024; Accepted: 9 May 2024; Published: 22 May 2024 Abstract: An abnormal noise problem was reported in a pickup truck equipped with a 2.0 L efficient engine during start-up. The noise was reproduced by the engine anechoic chamber bench for further analysis. NVH test (conducted through audio playback and signal filtering) showed that the noise had a signal of 1–3 kHz. Analysis through cylinder-by-cylinder oil-cutting method found that the abnormal noise completely disappeared after the fourth cylinder was cut off, indicating that the noise was related to the combustion of the fourth cylinder. The combustion characteristics of each cylinder were then analyzed in the starting condition through the Kibox combustion analyzer. The noise appeared after the first fuel injection of the fourth cylinder, and the maximum pressure rise rate was 42 Bar/°, confirming that the abnormal noise was combustion noise. Further tests on the physical fuel injection signal of each cylinder found that the fourth cylinder only had the main injection signal with no pilot injection signal. Further analysis of the synchronization signal recognition method of the model and the underlying logic of the fuel injection program showed that the synchronization signal was recognized for the first time in the starting process after the calculation moment of the 4th cylinder pre-injection program, resulting in the failure of the pre-injection calculation. Finally, the bottom fuel injection interrupt program was pushed back (60° to the crankshaft angle), ensuring smooth injection of the 4th cylinder pilot injection in the starting working condition, thus solving the abnormal noise without impacting engine performance.

Evaluation of plastic injection molding for PA6/ABS/CaCO3 nanocomposites using Taguchi method and Moldflow simulation approach

Nowadays, nanocomposites are widely used in the industry. Polymer nanocomposites are widely used in the automotive industry because they have very favorable properties. These properties, including mechanical, electrical, and thermal characteristics, change depending on the combination of materials used in composite synthesis. In this paper, the injection molding of an automobile part called a control arm protector is investigated. Since warpage and shrinkage are general and important challenges in injection molded parts, Taguchi test design and Autodesk Moldflow® simulation approach are used to find the best injection condition for the mentioned part. To perform this, PA6/ABS polymer composite combined with nano CaCO3 is used. Three main injection molding process parameters, including melt temperature, mold temperature, and injection pressure, as well as nano CaCO3 amount, are evaluated. Moreover, analysis of the gate location is investigated. In the following, an analysis of variance is conducted to identify the significant parameters. Regression correlations were also established. Finally, optimization of the process is carried out by the desirability method.

Optimizing Fuel Injection Timing for Multiple Injection Using Reinforcement Learning and Functional Mock-up Unit for a Small-bore Diesel Engine

<div>Reinforcement learning (RL) is a computational approach to understanding and automating goal-directed learning and decision-making. The difference from other computational approaches is the emphasis on learning by an agent from direct interaction with its environment to achieve long-term goals [<span>1</span>]. In this work, the RL algorithm was implemented using Python. This then enables the RL algorithm to make decisions to optimize the output from the system and provide real-time adaptation to changes and their retention for future usage. A diesel engine is a complex system where a RL algorithm can address the NO<sub>x</sub>–soot emissions trade-off by controlling fuel injection quantity and timing. This study used RL to optimize the fuel injection timing to get a better NO–soot trade-off for a common rail diesel engine. The diesel engine utilizes a pilot–main and a pilot–main–post-fuel injection strategy. Change of fuel injection quantity was not attempted in this study as the main objective was to demonstrate the use of RL algorithms while maintaining a constant indicated mean effective pressure. A change in fuel quantity has a larger influence on the indicated mean effective pressure than a change in fuel injection timing. The focus of this work was to present a novel methodology of using the 3D combustion data from analysis software in the form of a functional mock-up unit (FMU) and showcasing the implementation of a RL algorithm in Python language to interact with the FMU to reduce the NO and soot emissions by suggesting changes to the main injection timing in a pilot–main and pilot–main–post-injection strategy. RL algorithms identified the operating injection strategy, i.e., main injection timing for a pilot–main and pilot–main–post-injection strategy, reducing NO emissions from 38% to 56% and soot emissions from 10% to 90% for a range of fuel injection strategies.</div>

A novel concept of active pre-chamber engine with a single injector – The passive main chamber approach

The pre-chamber spark ignited combustion is recognized as one of the most promising concepts utilizing a lean burn combustion approach towards the increase of efficiency and reduction of NOx emissions in spark ignited engines. Numerous investigations indicate the possibility to reduce the engine-out NOx emissions under the regulation limits by using active pre-chamber at very high dilution levels. Regardless of the dilution approach, one of the main challenges is to achieve the proper mixture formation and scavenging of the pre-chamber from residual gases to ensure stable engine operation without misfires. Recent investigations imply that the auxiliary air injection in the pre-chamber might be necessary to ensure stable operation at such highly diluted mixtures, especially if an EGR dilution approach is utilized, further increasing the complexity of such a concept. In this work, a new approach is investigated which can be described as a passive main chamber approach and relies on a single fuel injector supplying both the pre-chamber and the main chamber. Contrary to the passive pre-chamber systems, the injector in this approach is mounted in the pre-chamber, while the main chamber is supplied indirectly through the pre-chamber nozzles. To verify the feasibility and the potential benefits of such an approach, a numerical framework consisting of 3D-CFD and 1D/0D models is applied. The performed study included different pre-chamber variants, previously investigated on an experimental gasoline-fuelled engine, to verify the applicability of such a concept regardless of the pre-chamber geometry. The performed study showed that the proposed concept is a feasible option and, despite the inability to directly control the excess air ratio in the pre-chamber, results with the desired values of λPC ≈ 0.8 at the MBT optimized spark timings. At very lean mixtures (λglobal > 2.0), the average residual gas concentration in the pre-chamber and around the spark plug at the ignition timing is reduced from 10 % and 13 % respectively to 2.5 %, along with a 1.4 percent point increase of indicated efficiency when compared to normal operation. When compared to the reference gasoline fuelled cases, a highest efficiency of 37.7 % is achieved at moderately lean mixture (λglobal ≈ 1.6) and MBT optimized spark timing with NOx levels of 1.41 g/kWh, which represents a 0.7 percent point increase in indicated efficiency but 75 % increase of NOx emissions. At NOx optimized spark timing however (NOx < 0.4 g/kWh), an identical indicated efficiency of 34.7 % is obtained. Overall, the results indicate that with the proposed concept, it is possible to achieve the same scavenging effect as with auxiliary air injection while eliminating the need for both the main chamber injection system and the pre-chamber auxiliary air supply system and without sacrificing the overall performance.

Study on the productivity and mechanism of physical field evolution of enhanced geothermal systems under different working fluid types and properties

The injected working fluid conditions directly affect the heat generation efficiency of a stimulated hot dry rock reservoir. Taking exploration well GR1 in the Gonghe Basin of Qinghai as the research object, a stochastic discrete fracture reservoir model was established around the main injection channel, and the productivity variation pattern of the enhanced geothermal system (EGS) and the spatiotemporal evolution mechanism of the reservoir fields were analyzed for CO2 and H2O working fluids. The interaction mechanism between the upper and lower rock formations and the reservoir during the heat mining process was discussed. This study obtained the following findings: (1) when the working fluid was CO2, after 20 years of heat recovery, the injection flow rate, output flow rate, and heat generation efficiency with a working fluid temperature of 60 °C reached 1.22 times, 1.18 times, and 1.92 times those with a working fluid temperature of 35 °C, respectively. The average subsidence and average geostress with the working fluid temperature of 60 °C were low, at only 90.61% and 95.96% of those with the working fluid temperature of 35 °C, respectively. However, high-temperature fluid injection increased flow loss. The changes in the various laws of H2O-EGS were similar to those of CO2-EGS. (2) When the working fluid temperature was 35 °C, after 20 years of heat recovery, the output flow rate and heat generation efficiency with the CO2-EGS reached 12.66 times and 1.28 times those with the H2O-EGS, respectively. However, the flow loss, average subsidence, and average geostress were higher with the CO2-EGS, reaching 6.58 times, 1.14 times, and 1.06 times those with the H2O-EGS, respectively. The patterns in these parameters observed at the other temperatures were similar to those observed at 35 °C. (3) The temperature decrease of the cushion layer was higher than that of the caprock, while the subsidence of the caprock was higher, and this phenomenon was more obvious when the working fluid temperature was lower. The conclusions obtained have important reference significance for the rational selection of working fluids.

Ammonia fueled engine with diesel pilot ignition: Approach to achieve ultra-high ammonia substitution

Ammonia is a hydrogen-rich zero-carbon fuel, and is one of the most promising approaches to realize energy decarbonization in the fields of industry and transportation. Efficient operation and emissions control have been the primary obstacle to develop engines with high ammonia energy share. In this study, the combustion and emissions of an ammonia-fueled engine with diesel pilot ignition are investigated, and the target is to achieve ultra-high ammonia substitution with acceptable thermal efficiency. The ammonia energy share is first increased from 30% to 90% at an intermediate load, with a split diesel injection triggering ammonia combustion. It found that the increased ammonia energy share reduces the indicated thermal efficiency from 48.3% to 38.9% with high unburned ammonia emissions. The NOx emissions exhibit a turning point with increased ammonia substitution, which indicates that the NOx emissions transition from the thermal-dominated to the fuel-dominated regime. The diesel pilot injection strategy is then optimized, by advancing the main injection timing and changing the pre-injection amount and the interval between two injection events. Optimized diesel injection controls the ignition timing and combustion process, thereby improving thermal efficiency and emissions at high ammonia energy shares. An ultra-high ammonia energy share of 95% could be finally achieved, and the thermal efficiency is 40.2%. It is also noted that as engine load increases, engine thermal efficiency at an ammonia energy share of 80% could be elevated to 44.2%.

Experimental investigation on in-cylinder working process and thermal efficiency of ammonia/diesel low-carbon engine with pre-injection strategy

Ammonia, as a zero carbon and sustainable fuel, combined with traditional diesel fuel can provide a promising solution for reducing the engine environmental impact. However, ammonia/diesel dual-fuel (ADDF) engine has the significant drawback of low combustion efficiency and poor combustion stability at low loads, which seriously hinders its development. Therefore, this study explored the potential of pre-injection strategy in improving the performance of ADDF engine, comprehensively evaluating the effects of four pre-injection parameters (main injection timing (MIT), pre-injection timing (PIT), pre-injection quantity (PIQ), and diesel injection pressure (DIT)) on in-cylinder combustion process, incomplete combustion emissions, and energy efficiency. The results indicate that MIT has the most significant impact on combustion process. Advancing MIT can significantly increase in-cylinder combustion pressure and reduce CO, HC and unburned NH3 emissions. At MIT = -12 °CA ATDC, the highest brake thermal efficiency (BTE) of 32.3 % is obtained, while simultaneously generating high combustion noise. The advance of PIT has adverse effects on combustion stability. When PIT is advanced from −24 °CA ATDC to −36 °CA ATDC, COVIMEP increases from 2.61 % to 4.44 %, unburned NH3 emission increases by 23.5 %, and the BTE of ADDF engine decreases. Adjusting the PIQ and DIP can improve the reactivity distribution of fuel and reduce incomplete combustion emissions. However, the decrease in main injection quantity would increase the cycle fluctuation. At low loads, shortening the pre-main injection interval and increasing PIQ and DIP can enable the engine to achieve higher BTE while reducing pollutant emissions. This study elucidates in detail the influence of four pre-injection parameters on the operation characteristics of ADDF engine. It can offer insights and practical references for expanding the operating range of ammonia fuel engine.