Engine Test Research Articles

Unique High-Resolution Temperature Mapping of Stage 1 Turbine Vane in a Long-Term Engine Test

Abstract In this study, surface temperature maps resulting from a long-term engine test were evaluated on a stage 1 turbine vane using thermal history coatings (THCs). THCs are ceramic-type sensor coatings doped with a lanthanide ion, giving the coating photoluminescent properties. The THC's structure permanently changes when exposed to high temperatures, which in turn alters its photoluminescent properties. Therefore, historic maximum temperature maps are evaluated by optically probing the THC point-by-point across the vane's surface. The vane was exposed to a non-dedicated (multi-cycle, multi temperature-level) engine test lasting over 8 months. Two passes of THC measurements were taken, termed low resolution (LR) and high resolution (HR), each, respectively, with point pitches of 5 mm and 1 mm. The latter provided a unique insight into the historic maximum temperature profile of the vane, particularly around high-temperature gradient regions, such as those close to effusion cooling holes. The THC temperatures were compared to the engine manufacturer's (Doosan Enerbility) heat transfer code (Doosan Integrated Thermal Analysis for Cooling System (DiTACS)) for validation. The THC temperature mapping was successful with good coverage across the vane. The leading edge and pressure side trailing edge regions were typically the hottest. The HR measurements clearly show sharp thermal gradients around the effusion cooling holes on the vane's airfoil and platforms. Critically, the THC measurements were compared very well to the DiTACS measurements, validating THCs as a credible temperature measurement technique for long-term, non-dedicated engine tests for components operating in some of the most extreme environments of an engine.

Numerical Investigation of CO and NO Production From Premixed Hydrogen/Methane Fuel Blends

Abstract There is significant interest in utilizing hydrogen as an energy carrier in a net-zero carbon energy economy. A variety of fundamental and practical issues associated with premixed hydrogen/methane combustion must be addressed, particularly flame flashback, combustion instabilities, and NOx emissions. Significantly less attention has been given to CO emissions from hydrogen blending. However, recent H2 blending engine tests have clearly noted major reductions in CO emissions, reductions which substantially exceed what would be expected based upon C atom mass balances in the fuel. Moreover, NOx, CO, and combustor operability always tradeoff with each other, and so, for example, these CO reductions can also enable operational or design modifications to reduce NOx emissions and/or wider operability windows. This paper addresses H2 blending effects on CO emissions, addressing both the direct influences on CO emissions, as well as how it influences NOx–CO tradeoffs. The paper presents computations that differentiate between the kinetic and equilibrium effects of H2 blending, as well as how H2 blending can lead to reductions in both NOx and CO by moving the Pareto front downward. Finally, this work suggests that H2 blending, in addition to its CO2 reductions, can also increase plant operational flexibility and so provide additional value propositions to an evolving electricity market.

Analysis of factors affecting the stability of aircraft engine test

Abstract Although the aircraft is in a braking and shutdown state during engine testing, there may still be situations where the aircraft slides or deviates during the development process, which affects the safety of the aircraft. This article establishes a force analysis model for an aircraft engine test and proposes a single-engine testing force analysis method based on dual-engine testing force analysis. Factors such as the friction coefficient of pavement, wind speed, and aircraft parking slope are taken into account in the calculation. The relationship between different influencing factors and ground stability is studied in the article. The article provides a reference for the weight center of gravity limitation of aircraft under engine ground testing conditions.

Influence of Engine Oil Degradation on Sliding Bearings, with Special Focus on Different Degrees of Nitration

Bismuth (Bi) can be considered for use as a green substitute for lead in bearing applications. However, accelerated Bi oxidation can occur during operation, creating a brittle surface and resulting in premature seizure failure. Thus, the aim of this study was to evaluate the influence of engine oil degradation, especially nitration processes, on the oxidation of Bi. Tailor-made artificially aged oils with different degrees of nitration were produced and utilized in static bearing oxidation tests. By means of X-ray photoelectron spectroscopy (XPS), the Bi surfaces were analyzed regarding their chemical compositions after the tests. The results were correlated with the respective oil conditions determined via conventional parameters as well as high-resolution mass spectrometry. The findings obtained revealed a direct correlation between the amount of Bi-oxide and the nitration values of the oil, proving there was a positive impact of nitration products on the oxidation of the Bi surfaces. A comparison with the Bi content in the oils demonstrated a protective effect of the oxide layer as the Bi content declined with an increase in nitration. Overall, valuable insight into understanding the impact of oil condition on engine parts is given, and the importance of testing engine parts with aged lubricants is emphasized.

Performance and emissions of a CI engine using a diesel, jatropha biodiesel and biodiesel adopting Al2O3 nanomaterial as fuel blend.

A nanocomposites of aluminum dioxide was employed as a fuel additive in a compression engine test. Nanoparticle stability in diesel was measured by their impact on the fuel's flash point, density, and viscosity. When compared to other forms of fuel, conventional biodiesel has superior qualities. Al2O3 was also put through its paces in terms performance of engine and pollution testing. The thermal efficiency of the engine's brakes may be improved by adding nanoparticles in to the jatropha biodiesel. Using Al2O3 nanoparticles has been shown to reduce brake-specific fuel consumption by 23%. In addition, this solution can cut hydrocarbon emissions by 19%.

Diagnosis of marine internal combustion engines by means of rapidly variable temperature and composition of exhaust gas as an alternative or support for currently used diagnostic methods

The article points out relevance of parametric diagnostics of ship engines and analyzes the state of research in this field. A method is proposed for diagnosing engine systems on the basis of rapidly variable exhaust temperature while measuring its composition. A method for determining diagnoser tools from the signal within one engine cycle and mathematical and statistical treatment of test results is presented. The products of numerical moddeling in the Diesel-RK software and the products of laboratory research on a Farymann Diesel test engine were analyzed. Affect of the most popular defects on the analyzed parameters was defined. Criteria for matching a diagnoser tool in accordance with the type of damage in a ship engine was presented. A methodology was proposed for adapting the presented method to metering on a ship engine in operation.

Development of Self-Help Lifting Pads for Elderly People with Difficulty in Sitting Up

As individuals age, physiological changes can make it increasingly difficult to sit up unassisted. This study aimed to develop ergonomic self-help lifting pads to aid elderly individuals. The first phase involved constructing the pads and a needs assessment with elderly participants and caregivers to survey the physical dimensions and requirements for the design. The second phase focused on cost, engineering, and usage efficiency. Cost efficiency was analyzed using descriptive statistics, engineering efficiency was assessed through testing seat cushion, force reduction, and electrical safety, and usage efficiency was evaluated with participants aged 40 to 50 years. Results from the first phase indicated that the pads should be at least 53.15 cm wide and 153 cm long, with a need for relaxation and affordability. In the second phase, prototype pads were developed according to these specifications. A cost analysis showed that while the manual pad was more expensive than comparable products, the other variants were more cost-effective. Engineering tests confirmed that the cushions met ASTM D3574 standards and that the electrical components conformed to IEC 60335 standards. Usage efficiency ratings were the highest for the massage system pad. Participant feedback indicated longer pads, more convenient controls, and increased cushion comfort, guiding the development of the second version.

A Real-Time System Status Evaluation Method for Passive UHF RFID Robots in Dynamic Scenarios

In dynamic scenarios, the status of a Radio Frequency Identification (RFID) system fluctuates with environmental changes. The key to improving system efficiency lies in the real-time monitoring and evaluation of the system status, along with adaptive adjustments to the system parameters and read algorithms. This paper focuses on the status changes in RFID systems in dynamic scenarios, aiming to enhance system robustness and reading performance, ensuring high link quality, reasonable resource scheduling, and real-time status evaluation under varying conditions. This paper comprehensively considers the system parameter settings in dynamic scenarios, integrating the interaction model between readers and tags. The system’s real-time status is evaluated from both the physical layer and the Medium Access Control (MAC) layer perspectives. For the physical layer, a link quality evaluation model based on Uniform Manifold Approximation and Projection (UMAP) and K-Means clustering is proposed from the link quality. For the MAC layer, a multi-criteria decision-making evaluation model based on combined weighting and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) is proposed, which comprehensively considers both subjective and objective factors, utilizing the TOPSIS algorithm for an accurate evaluation of the MAC layer system status. For the RFID system, this paper proposes a real-time status evaluation model based on the Classification and Regression Tree (CART), which synthesizes the evaluation results of the physical layer and MAC layer. Finally, engineering tests and verification were conducted on the RFID robot system in mobile scenarios. The results showed that the clustering average silhouette coefficient of the physical layer link quality evaluation model based on K-Means was 0.70184, indicating a relatively good clustering effect. The system status evaluation model of the MAC layer, based on the combined weighting-TOPSIS method, demonstrated good flexibility and generalization. The real-time status evaluation model of the RFID system, based on CART, achieved a classification accuracy of 98.3%, with an algorithm runtime of 0.003 s. Compared with other algorithms, it had a higher classification accuracy and shorter runtime, making it well suited for the real-time evaluation of the RFID robot system’s status in dynamic scenarios.

A Study of Heat Recovery and Hydrogen Generation Systems for Methanol Engines

Biofuels are the most essential types of alternative fuels, which currently have significant potential to reduce CO2 emissions compared to fossil fuels. Methanol is a more efficient fuel than petrol due to its physicochemical properties, such as a higher latent heat of vaporization, research octane number, and heat of combustion of the fuel–air mixture. Also, biomethanol is cheaper than traditional petrol and diesel fuel for agricultural countries. The authors have proposed a new approach to improve the characteristics and efficiency of methanol diesel engines by using biomethanol mixed with hydrogen instead of pure biomethanol. Using a hydrogen–biomethanol mixture in modern engines is an effective method because hydrogen is a carbon-free, low-ignition, highest-flame-rate, high-octane fuel. A small quantity of hydrogen added to biomethanol and its combustion in an engine with a heat exchanger increases the combustion temperature and heat release, increases engine power, and reduces fuel consumption. This article presents experimental results of methanol combustion and a hydrogen-in-methanol mixture if hydrogen was retained due to the utilization of the heat of the exhaust gases. The tests were carried on a single-cylinder experimental engine with an injection of liquid methanol and gaseous hydrogen mixtures. The experiments showed that green hydrogen generated onboard the car due to the utilization of heat significantly reduced fuel costs of engines of vehicles and technological installations. It was established a hydrogen gaseous mixture addition of up to 5% by mass to methanol requires a corresponding change in the coefficient of excess air to λ = 1.25. Also, using an additional hydrogen mixture requires adjustment at the ignition moment in the direction of its decrease by 4–5 degrees of the engine crankshaft. Hydrogen gas mixture addition reduced methanol consumption, reaching a maximum reduction of 24%. The maximum increase in power was 30.5% based on experimental data. The reduction in the specified fuel consumption, obtained after experimental tests of the methanol research engine on the stand, can be implemented on the vehicle engines and technological installations equipped with an onboard heat recovery system. Such a system, due to the utilization of heat and the supply of additional hydrogen, can be implemented for engines that work on any alternative or traditional fuels.

Design of substation grounding grid in CFETR

This paper aims to propose a method for the design of the substation grounding grid in China Fusion Engineering Test Reactor (CFETR). In order to evaluate the safety of the grounding grid, Electrical Transient Analysis Program (ETAP) was used to simulate the fault current, contact voltage, and step voltage, and the results are compared with theoretical calculations to verify the correctness of the design. This will help reduce faults caused by the defects of grounding grid This method is special in that the designed grounding grid not only meets the requirements of relevant standards, but also reduces the number of conductors. During the design process, factors such as voltage level, fault location, and soil resistivity were fully considered to adapt to different occasions. This method can also guide the design and renovation of grounding grids for other buildings in CFETR.

Construction of Virtual Experiment Teaching Platform based on 5E Teaching Mode and VI Technology

Virtual instruments have many advantages such as low cost, comprehensive functionality, easy scalability, and easy replication. At the same time, they can also meet the special requirements of time and space for remote experiments. Based on Web technology and virtual instrument technology, a virtual experiment system is constructed, which combines data sharing, remote control, and real-time operation. More conducive to utilizing experimental and scientific research resources. At the same time, virtual instruments have high flexibility and are no longer limited by traditional experimental teaching modes, which can save a lot of repeated investment costs. They can also keep the teaching equipment in the laboratory up-to-date and closely follow the development trend of science and technology. As a compulsory course for mechanical engineering majors, although the existing experimental system has achieved certain results, there are still limitations to 'Mechanical Engineering Testing Technology'. This article aims to address the problems of insufficient instrument sets and outdated equipment in the experimental teaching of "Mechanical Engineering Testing Technology", as well as students' poor ability to apply theory to practice and insufficient innovation ability. By integrating the 5E teaching mode, a virtual experimental teaching platform based on VI (Virtual Instrument) technology is established. Students can break through traditional experimental methods and conduct various experiments through the network, obtaining experimental experiences that are very similar to real experiments. At the same time, it can deepen their understanding and recognition of experiments, and better grasp theoretical knowledge.

The Coefficient of Reactivity and Activation Energy as the Criteria of Assessment of the Influence of Sustainable Aviation Fuels on Combustion Process in a Rapid Compression Combustion Machine and a Turbine Engine

Aviation in Europe is required to use fuels containing up to 2 wt. % of sustainable aviation fuels (SAFs). A better understanding of the impact of SAFs on the combustion process will be helpful in solving problems that may arise from the widespread use of these kinds of fuels. It was assumed that the reactivity coefficient αi and the activation energy could be a criteria for assessing the impact of SAFs on the combustion process. Based on DGEN engine tests, the following activation energy values of CO2 and CO formation reactions were obtained—Jet A-1: EaCO2/R=3480 and EaCO/R=982; A30: EaCO2/R=3705 and EaCO/R=2903; and H30: EaCO2/R=3637 and EaCO/R=2843. These results indicate differences in the structure of combustion reaction chains involved by the SAF addition to Jet A-1 fuel. The same conclusion has been formulated on the basis of the reactivity coefficient αi. The values of maximum cylinder pressure (Pmax) obtained during indicator RCCM (rapid compression combustion machine) tests correlated with both the activation energy and coefficients of reactivity. This suggests that the influence of SAF addition to Jet A-1 fuel on the structure of chemical reactions chain during RCCM tests is similar to the influence during DGEN 380 tests. The assumption stated above was confirmed. This indicates the possibility of the preliminary forecasting of CO2 and CO emissions from the DGEN 380 engine based on the test at the RCCM stand.

Joint subarray acoustic tweezers enable controllable cell translation, rotation, and deformation

Contactless microscale tweezers are highly effective tools for manipulating, patterning, and assembling bioparticles. However, current tweezers are limited in their ability to comprehensively manipulate bioparticles, providing only partial control over the six fundamental motions (three translational and three rotational motions). This study presents a joint subarray acoustic tweezers platform that leverages acoustic radiation force and viscous torque to control the six fundamental motions of single bioparticles. This breakthrough is significant as our manipulation mechanism allows for controlling the three translational and three rotational motions of single cells, as well as enabling complex manipulation that combines controlled translational and rotational motions. Moreover, our tweezers can gradually increase the load on an acoustically trapped cell to achieve controllable cell deformation critical for characterizing cell mechanical properties. Furthermore, our platform allows for three-dimensional (3D) imaging of bioparticles without using complex confocal microscopy by rotating bioparticles with acoustic tweezers and taking images of each orientation using a standard microscope. With these capabilities, we anticipate the JSAT platform to play a pivotal role in various applications, including 3D imaging, tissue engineering, disease diagnostics, and drug testing.

Characterize the influences of hydraulic fracturing on preventing rock burst from the stress and vibration fields

The thick and hard roof (THR) is a significant factor that induces rock burst incidents. Traditional deep-hole blasting methods struggle to effectively relieve pressure for the high-level THR on a large scale. Although the horizontal staged hydraulic fracturing technology can crack high-level rock stratas, its impact on roof fracture still needs to be clarified, and there need to be more effective methods to evaluate its pressure relief effect. This paper conducted a comparative engineering test of local hydraulic fracturing pressure relief and load reduction on the working face to address this gap. The key layer theory and mine earthquake distribution were used to identify potential hazards of rock strata and the fracturing strata. Revealed the spatial and temporal evolution rules of microseisms induced by mining work, the failure mechanism of high-energy mine earthquakes, the evolution characteristics of source mechanical parameters, and the evolution characteristics of the stope stress field. The results indicate that after fracturing microseisms during mining presented exhibit a uniform distribution of high frequency and low energy. The fracture fragmentation of the roof rock was reduced, and the range of mining disturbance was minimized. High-energy mine earthquakes induced by mining are transferred to the goaf. Simultaneously, the corner frequency and stress decrease while the rupture radius and the shear component of the failure mechanism increase. The integrity of the THR is compromised, and fracture propagates and slips along the pre-crack. The roof of the working face experiences localized pressure, with decreased periodicity and intensity, reducing the overall static load level of the coal seam under the fracturing area. The research findings serve as a valuable reference for further investigations into the mechanism and risk assessment of hydraulic fracturing in preventing and controlling rock burst.

Experimental Study on Ice Shedding Behaviors for Aero-Engine Fan Blade Icing during Ground Idle

Fan blade icing can affect efficiency and aerodynamic stability, and the shed ice may be sucked into the core of the engine, causing adverse effects or even damage to the compressor components. Ice accretion and shedding are among the key issues in engine design and tests. But they have not been clearly understood. In this work, ice shedding from rotating aero-engine fan blades during continuous icing is experimentally investigated under the relevant airworthiness requirements. The phenomena of icing and ice shedding under different ambient temperatures and engine speeds are recorded to obtain the ice-shedding time and the characteristic length of the residual ice. Force analysis is used to understand the corresponding behavior. The degree of ice-shedding balance Db is defined to explore the symmetry of ice shedding. The results show that the shedding time is significantly affected by the rotational speed, and the characteristic length will first shorten and then grow as the ambient temperature decreases. When the ice shedding is completed instantaneously, Db will show a violent shock. There is a critical ambient temperature, below which the ice accretion will worsen significantly as temperature decreases. For aero-engine fan blade icing tests during ground idle, the critical ambient temperature ranges from −5 ∘C to −9 ∘C. In order for the ice to shed faster, the engine speed has to reach a threshold. This study can shed light on the preliminary characteristics of ice shedding from rotating components and provide guidance and a data basis for the numerical simulation of fan blade icing and the design of an aero-engine.

Expanding the Capability of a Legacy Combustion Flame Tube to Test High-Temperature Engine Materials in Relevant Environments

Abstract New materials and component designs are needed to advance gas turbine engine technology and provide the performance and efficiency needs for future applications. In order to advance these materials, testing in combustion environments is a critical step prior to engine testing. In this work, we detail the design and the fabrication of a materials test sector in a flame tube combustor facility. The facility simulates a combustion environment similar to that experienced by components in gas turbine engines. The flow regime is characterized by a combination of high-temperature, high-heat flux, and high-velocity that components experience in gas turbine engines. Exposure of components in this facility allows for the study of combined environmental effects and the impact on both coating and substrate durability. The test facility may operate across a wide range of pressures from 275 to 400 psig (1896–2758 kPa) and an air flowrate of 5 lb/s (2.27 kg/s). While combustion gas temperature is expected in excess of 3000 °F (1649 °C), 900 °F (482 °C) cooling air may be supplied to the backside of components or test articles. The flame tube combustor was previously used to evaluate fuel injectors and combustion products, and the new test configuration will also allow for materials exposure to complex, engine-like conditions. The interior of the test section was additively manufactured from GRCop-84 and cryogenically fit and brazed to a stainless-steel 304 housing. The use of a copper liner minimizes welds and, with active cooling, is expected to provide better durability over traditional hardware using stainless-steel or Inconel with a ceramic liner. The test section has two opposing 9.5 in × 3.125 in (241 mm × 80 mm) removable windows that can accommodate articles up to 3.5 in (89 mm) tall. This modular design allows for custom platforms to hold coupons, panels, or airfoil shapes to be tested with minimal re-engineering or fabrication. The bolted joint and sealing remains consistent, so any new testing only needs to work within the existing design footprint. This paper will provide an overview of the facility capabilities, design considerations, as well as thermal and structural analysis of the hardware. Future testing of ceramic matrix composite (CMC) airfoils and advanced environmental barrier coatings (EBCs) will also be discussed.

Upconverting thermal history paint for investigations of short thermal events

The main goal of the work was to develop phosphorescent coating for investigations of surface temperature distribution resulted from short duration and high energy thermal events such as small rocket engine testing. For that purpose, we developed thermal history paint with upconverting Gd2O3: Er3+, Yb3+, Mg2+ nanopowder. The developed paint was heated by Joule effect with precise control over temperature and heating time. Photoluminescence signal of cooled samples was excited with 980 nm laser and collected in automatic manner with use of an optical fibre probe connected to photospectrometer. The results show that irreversible changes of paint emission are temperature and heating time specific for calcination temperatures from 700 °C to 1150 °C. Calibration curves were prepared for heating times of 10, 60 and 180 seconds. Finally, 2D surface temperature samples were determined with use of upconverting thermal history paint and compared to IR camera and pyrometric measurements. The results indicate that uncertainty of temperature measurement below 10 °C was achieved for temperatures above 1000 °C. It has been demonstrated that developed thermal history paint allows for measurements of 2D surface temperature distribution with high spatial resolution and good agreement to standard measurements techniques like thermal camera and pyrometer.

Assessing combustion characteristics of alternative fuels in a CI engine by use of a wavelet-based analysis of engine vibration signals

In the current work, a wavelet-based approach for assessing combustion performance of alternative fuels in compression-ignition engines, indicated that changes in cylinder pressure amplitude were reflected by commensurate changes in a proposed parameter, with a maximum of a 9% variation. The proposed parameter, the wavelet transform coefficient maximum amplitude (WMA), successfully accomplished this for various engine conditions. The wavelet transform coefficient standard deviation (WSD), a second proposed parameter, was able to track changes in the rates of pressure rise associated with changes in load conditions and fuel type, with a maximum variation in the parameter of 7%. The approach was assessed by testing six fuels in a test engine unit. Thermodynamic property data and vibration signal data were recorded for each of the fuels tested, at six loading conditions. Subsequently, combustion performance was evaluated using traditional thermodynamic parameters and using the WMA and WSD via a MATLAB based algorithm. Thus, it was surmised that the proposed approach can form the basis for a vibration-based assessment of alternative fuel combustion performance in reciprocating engines.

Experimentally Investigating the Potential of Iso-Stoichiometric GEM Blends as a Drop-in Replacement for E50 in SI Engines

Background: Research on alternative fuels for internal combustion engines is crucial due to climate change and energy security concerns. Ethanol-blended gasoline has been a popular alternative fuel, but biomass limitations restrict its widespread use. Methanol offers a solution as it can be produced from non-food sources, extending ethanol's availability. Objective: This study explores a ternary fuel blend consisting of gasoline, ethanol, and methanol as an alternative to binary gasoline-ethanol blend. The objective is to investigate if the isostoichiometric ternary blend offers equivalent fuel properties to E50 (Ethanol 50%, Gasoline 50% (v/v)) gasohol while potentially enhancing engine performance, reducing emissions, and improving combustion characteristics. Methods: A single-cylinder, four-stroke, port fuel injection spark ignition engine was used. The engine was tested with three fuels: pure gasoline, E50 blend, and an equivalent iso-stoichiometric GEM blends. Engine tests were conducted at constant load with varying engine speeds. Performance, emission, and combustion parameters were experimentally measured and compared across all fuels. Results: E50 and its equivalent blends improved brake thermal efficiency but increased brake specific fuel consumption compared to gasoline. It significantly reduced unburned hydrocarbon and carbon monoxide emissions but slightly increased nitrogen oxide emissions. Conclusion: Formulated E50 equivalent blends have identical air to fuel ratio, lower heating values as conventional binary E50 gasoline-ethanol blends. The study suggests that iso-stoichiometric GEM blends have the potential to be a viable alternative drop-in fuel for E50 in internal combustion engines. The future advancements in GEM blends, particularly in optimizing ratios, could lead to patentable inventions.

Effects of Diesel Pre-Injection Time on Combustion Process and Emission Characteristics of Diesel/Methanol Dual Fuel Engine

ABSTRACT The traditional diesel engine not only causes the reduction of nonrenewable energy but also aggravates environmental pollution. The utilization of renewable fuels in engine can not only effectively reduce the dependence on oil sources but also effectively reduce emissions. As a renewable oxygen-containing fuel with low production cost and widely sourced, methanol holds vast potential for application in engine. The dual-fuel combustion of diesel and methanol has emerged as an important research issue in the internal combustion engine industry. This paper conducted a study on the combustion and emission characteristics of the diesel/methanol dual fuel based on the optical engine test platform and 3D numerical simulation software. The results show that the change in cylinder pressure is relatively small and the heat release rate increases with the advance of diesel pre-injection time. The pre-injection time of diesel mainly affects the mixture distribution of pre-injection diesel, and the mixture is more evenly mixed with the advance of the pre-injection time. The degree of premixed combustion becomes higher, premixed combustion will lead to more rapid combustion, so the peak heat release rate shows an increasing trend. The pre-injection time of diesel is advanced, resulting in a leaner mixture in the early stage, and the fuel is not easy to burn, so CA10 and CA50 are delayed. The soot formation decreases as the mixture becomes more uniform, and the number of pixels of KL factor in each range also decreases. The average temperature in the cylinder is reduced and the NOX shows a decreasing trend with the advance of the pre-injection time. The change in CO generation is relatively small with the advance of pre-injection time.