Two-stroke Engine Research Articles

Toward zero carbon emissions: High thermal efficiency low speed two-stroke marine engine using pure ammonia fuel

As the future development trend and the crucial link to achieving the carbon peaking and carbon neutrality goals in China, the achievement of “zero carbon” emissions in low-speed two-stroke marine engines is currently in the preliminary stages of exploration. Ammonia fuel is one of the main zero-carbon energy sources of interest for marine engines. The primary challenges associated with ammonia application include its high self-ignition temperature, low laminar flame speed, and lengthy ignition delay time. Although stable combustion can be achieved with the assistance of a small amount of highly active carbon-based fuel, carbon emissions are still inevitable. To obtain “zero carbon” emissions, the high-temperature cylinder gas recirculation strategy (HTCGR) was innovatively proposed to realize the possible application of pure ammonia. However, the heat transfer loss by using pure ammonia fuel is enhanced by 289% compared to the diesel mode. Therefore, the main objective of this article is to investigate ways to decrease heat transfer loss and further improve the thermal efficiency of the two-stroke engine from the perspective of energy distribution, and the effect of the circulating high-temperature gas, swirl ratio, and fuel distribution on heat transfer loss was systematically numerically studied in this manuscript. As a result, the heat transfer losses can be decreased up to 38.80% by lowering the CGR rate and adjusting the fuel distribution, and the ITE can be improved from 48.85% in the diesel model to 51.19% in the ammonia mode. However, to avoid incomplete combustion in the engine, a minimum CGR rate of 13.3% is basically required for the compression ignition of pure ammonia fuel.

Integration of objective weighting methods for criteria and MCDM methods: application in material selection

Determining weights for criteria is an extremely crucial step in the process of selecting an option based on multiple criteria, also known as Multi-Criteria Decision Making (MCDM). This article presents the combination of five objective weighting methods for criteria with three MCDM methods in the context of material selection. The five objective weighting methods considered are Entropy, MEREC (Method based on the Removal Effects of Criteria), LOPCOW (Logarithmic Percentage Change-driven Objective Weighting), CRITIC (Criteria Importance Through Intercriteria Correlation), and MEAN. The three MCDM methods employed are MARA (Magnitude of the Area for the Ranking of Alternatives), RAM (Root Assessment Method), and PIV (Proximity Indexed Value). Material selection investigations were conducted in three different cases, including lubricant selection for two-stroke engines, material selection for manufacturing screw shafts, and material selection for manufacturing gears. The Spearman's rank correlation coefficient was calculated to assess the stability of ranking the alternatives using different MCDM methods. The combinations of objective weighting methods and MCDM methods were evaluated based on factors such as consistency in identifying the best material type, range, average value, and median of each set of Spearman's rank correlation coefficients. Two significant findings were identified. First, the weights of criteria calculated using LOPCOW method appear to be inversely related to those calculated using the Entropy method. Second, among the three MCDM methods used, MARA was identified as the most suiTable for lubricant selection for two-stroke engines, RAM was found to be the most suiTable for material selection for screw shafts and gears. The best material type in each case was also determined

Modeling and simulating axial vibrations on the crarkshaft of the large two-stroke marine diesel engine

The axial vibration is the strong vibrated phenomenon occurring on the main propulsion using a large two-stroke marine diesel engine. This article researches to build a mathematical model of the axial stiffness coefficient and force generated by the geometric configuration of the crank pin-crank web assemblies and the combustion gas force. The numerical simulation is performed by finite element method, using ANSYS software, applied to the main engine MAN B&W 6G70ME. Keywords: Axial stiffness; crank pin–crank web set; axial force; diesel crankshaft; large two-stroke marine diesel engine; Axial vibration simulation.

Research on Scavenging Flow Dynamics of Marine Two-Stroke Engines With a CFD-Derived Quasi-Dimensional Model

The complex in-cylinder gas state and flow significantly affect fuel-air mixture, combustion efficiency and emissions. However, the scavenging CFD model of large bore marine engines in digital twin system requires substantial computational resources. Therefore, a fast-run phenomenological model of the scavenging process is built in this study. The model simulates the thermal states and flow dynamics of inlet and exhaust gas based on the energy and momentum conservation principles, considering the ideal in-cylinder swirl velocity profile with effects of air mass loss, wall friction, and swirl shear. The model’s accuracy is confirmed by comparing it with CFD simulations on different engines, showing an average relative error less than 3.5%. It also analyzes the impacts of intake pressure. The model provides accurate boundary conditions for subsequent fuel spray, combustion, and emission simulations and can be combined with these models in the future, thereby applied to engine design, diagnostics, and control.

Experimental study on reducing BC emissions from a low-speed marine engine by using blended biodiesel and a nitro additive

The aim of this study was to evaluate the emission reduction effect of using waste oil biodiesel/diesel binary fuel and a nitro additive on black carbon (BC) emissions from a large marine engine fueled by heavy fuel oil (HFO). We conducted steady-state conditions tests on a low-speed two-stroke marine engine, where pure distillate diesel (D100), blended biodiesel (blending ratios of 10%, 30%, and 50%), low-sulfur heavy fuel oil (LSFO), high-sulfur heavy fuel oil (HSFO), and a nitro additive were tested, and the BC emission concentrations from the engine were measured under different conditions using a filter-type smoke meter (FSM) and a photoacoustic smoke meter (PAS). The results indicated that BC emissions from the engine were significantly decreased when blended biodiesels were used, with the decline rate increasing as the engine load increased, reaching a maximum reduction of 73% and 94% under 75% and 100% load compared to the use of HFOs, respectively. However, the use of biodiesel slightly increased the brake specific fuel consumption (BSFC) and NOx emissions. The nitro additive was blended with LSFO and HSFO at a ratio of 1:1200, respectively. It was observed that the introduction of the nitro additive led to a significant reduction in BC emissions compared to the use of pure HFOs. But different from the case of using blended biodiesels, the decline rate of BC decreased with increasing engine load. The BC emissions from LSFO and HSFO were decreased by approximately 10% and 25% under 25% load, respectively, the corresponding BSFC decreased by 5.88% and 3.71%, respectively, while the NOx emissions increased by 11.59% and 34.58%, respectively. In addition, the BC emissions measured by the FSM were on average 38.56% and 43.53% higher than those of the PAS when LSFO and HSFO were used, respectively.

Design assessment of the range of permissible operation modes of a marine two-stroke diesel engine

In the practice of operating marine diesel engines, as a limiting characteristic for mechanical stress, a characteristic corresponding to a constant effective torque, which is proportional to the average effective pressure, is used. There is no such unambiguity regarding the restrictive characteristics of thermal intensity. Limitations on the thermal stress of a diesel engine depend on its design features and the efficiency of the cooling system of the cylinder-piston group. At the diesel engine design stage, it is important to assess in advance whether the operational characteristics correspond to the technical specifications.
 The work carried out computational and theoretical studies of the operational parameters of the main marine two-stroke diesel engine operating according to the screw characteristic, which affect its mechanical and thermal stress, and determined the expected limiting characteristics of the mechanical and thermal stress. The studies were carried out for wide ranges of changes in the weight coefficient of the screw characteristics and the relative power of the diesel engine. The estimated design ranges of diesel operating modes are given, excluding its mechanical and thermal overload, and an assessment of the permissible weighting of the screw characteristics is given. The results obtained were compared with the characteristics of a marine four-stroke diesel engine.

Effects of natural gas admission location and timing on performance and emissions characteristics of LPDF two-stroke engine at low load

Low-pressure gas-admission marine two-stroke engines have significant potential for reducing emissions in the shipping industry. However, they exhibit poor combustion quality under low-load conditions, leading to lower thermal efficiency and high levels of HC and CO emissions. This study numerically evaluated the impacts of the gas admission location and timing on engine performance and exhaust gas emissions under low load conditions. The study revealed that different gas admission locations form distinct NG-air stratifications. Lower gas admission locations resulted in longer ignition delays and shorter combustion durations. The unburned CH4 and CO emissions were significantly reduced by a maximum of 20.14% and 42.29%, respectively. A trade-off exists between NOx and N2O emissions owing to the different temperature conditions of their formation. The NOx emissions increased continuously as the gas admission location was lowered to a maximum of 3.4218 g/kWh; a value slightly above the Tier III emission standards. Advancing the timing of gas admission further decreased the ignition delay time, NOx, and unburned CH4 emissions. This study revealed that in-cylinder natural gas mixture stratification due to varying gas admission locations and timings can improve the combustion efficiency and exhaust gas emissions of a natural gas-diesel dual-fuel engine under low-load conditions.

Efforts to Improve Ship Main Engine Efficiency and Ensure Its Safety

Efforts to improve ship main engine efficiency and ensure its safety have been ongoing endeavors in the maritime industry, driven by the dual imperatives of economic competitiveness and environmental sustainability. The main engine of a ship serves as its heart, propelling it through the vast expanses of the world's oceans while consuming significant quantities of fuel. Therefore, enhancing its efficiency directly impacts operational costs and reduces the environmental footprint associated with maritime transport. One primary focus of improving main engine efficiency lies in the advancement of engine design and technology. Over the years, there has been a concerted effort to develop engines that offer higher power output while consuming less fuel. This has led to the emergence of more efficient engine designs, such as slow-speed two-stroke engines and high-pressure, common-rail fuel injection systems. These innovations optimize fuel combustion, minimize energy losses, and enhance overall propulsion efficiency. Moreover, ongoing research and development efforts are aimed at harnessing alternative fuels and propulsion technologies to further enhance efficiency and reduce environmental impact. LNG (liquefied natural gas) has gained traction as a cleaner-burning fuel alternative, offering significant reductions in sulfur oxides (SOx) and nitrogen oxides (NOx) emissions compared to traditional marine fuels. Additionally, the exploration of hybrid and electric propulsion systems holds promise for reducing greenhouse gas emissions and improving overall energy efficiency. Ensuring the safety of ship main engines is paramount to the reliability and operability of vessels at sea. A robust maintenance regimen is essential to identify and address potential issues before they escalate into costly failures or pose safety hazards. Routine inspections, preventive maintenance, and condition monitoring play crucial roles in detecting abnormalities, wear, and tear, allowing for timely interventions and repairs. Furthermore, advancements in predictive maintenance technologies, such as remote monitoring systems and data analytics, enable real-time assessment of engine performance and early detection of potential malfunctions. The ARAS method lacks the capability to handle ambiguity, subjective judgments, and coping with incomplete information. It relies on unbiased good judgment to address uncertainty, particularly in unknown and complex conditions, making it a valuable approach. The method provides options for sequencing and analysis based on facts and special cases, allowing selectors to express both optimistic and rational attitudes. While it appears numerical on paper, it offers the flexibility to create e-learning pathways tailored to individual needs, emphasizing the importance of mastery. The proposed integrated software for this method is both cost-effective and validated for suitability, ensuring its practical application. Advanced Engine Designs, Improved Monitoring and Maintenance, Enhanced Fuel Management, Innovative Propulsion Technologies, Automation and Remote Monitoring and Advanced Materials and Coatings. the Rank Efforts to improve ship Main Engine efficiency and Ensure its safety for Additive Ratio Assessment method. Advanced Materials and Coatings is showing the highest rank and Advanced Engine Designs is showing the lowest rank. Fuel Efficiency Improvement, Emissions Reduction, Reliability and Maintenance Costs and Safety Performance.

A fuzzy Bayesian network risk assessment model for analyzing the causes of slow-down processes in two-stroke ship main engines

ABSTRACT This paper presents a risk assessment approach for analyzing the causes of malfunction-related main engine slowdowns. A fuzzy Bayesian Network-based methodology is used to assess the factors contributing to the engine’s slow-down processes. The model addresses the complexity and uncertainty inherent in maritime operations with fuzzy sets where numerous interrelated factors can affect engine performance, and the Bayesian network to capture probabilistic dependencies. It considers various potential causes of the slow-down of ship engines that the manufacturer provides. Results demonstrate the model's ability to identify the influential factors leading to engine slow-down events and quantify the overall risk. Integrating fuzzy logic and Bayesian Networks comprehensively assesses relevant risk factors. It enables maritime stakeholders to manage engine performance and improves operational safety proactively. Findings can inform decision-makers, enabling the implementation of targeted maintenance strategies, fuel quality control measures, and crew training programs in the maritime industry.

Effects on of Blended Biodiesel and Heavy Oil on Engine Combustion and Black Carbon Emissions of a Low-Speed Two-Stroke Engine

Abstract The effects of heavy fuel oil and biodiesel blends on engine combustion and emissions were studied in a marine two-stroke diesel engine. The engine was operated under propeller conditions using five different fuels with biodiesel blends of 10% (B10), 30% (B30), 50% (B50), and sulphur contents of 0.467% low sulphur fuel oil (LSFO) and 2.9% high sulphur fuel oil (HSFO). Tests have shown that using a biodiesel blend increases the engine fuel consumption due to its lower calorific value. Heavy fuel oil has a high Polycyclic aromatic hydrocarbons (PAH) content, which leads to higher exhaust temperatures due to severe afterburning in the engine. A comparison of engine soot emissions under different fuel conditions was carried out, and it was found that the oxygen content in biodiesel promoted the oxidation of soot particles during the combustion process, which reduced the soot emissions of biodiesel. Compared to HSFO, B10, B30, B50 and LSFO, the soot emission concentrations were reduced by 50.2%, 56.4%, 61% and 37.4%, respectively. In our experiments, the soot particles in the engine exhaust were sampled with a thermal float probe. Using Raman spectroscopy analysis, it was found that as the biodiesel ratio increased, the degree of carbonisation of the soot particles in the exhaust became less than that in the oxygenation process, resulting in a decrease in the degree of graphitisation.

Exploring Low-Speed Marine Diesel Engine Parameters through Advanced 3D Visualization with Delaunay Triangulation

The article presents an algorithm for creating software leading to the optimization of the combustion process of marine engines. Parameters determining the Existing Ships Energy Efficiency Index (EEXI) related to ship type, capacity, and propulsion principle are considered. Test data on the characteristics of a two-stroke main engine, model HYUNDAI 6S60MC-C for six types of loads were used as the basis. To present the working field of the engine, the necessary calculations have been carried out and dependencies have been derived for the power and the specific fuel consumption as a function of the revolutions. The implementation includes the development of a small software program using Delaunay's triangulation algorithm to create 3D graphics, as well as Python libraries and methods.

Influence of oxyhydrogen gas retrofit into two-stroke engine on emissions and exhaust gas temperature variations

The generation of power and fuel sustainability that contributes to a cleaner output of exhaust gases is one of the most important objectives the world seeks. In this paper, oxyhydrogen gas is used to retrofit into a two-stroke engine. The water was electrolysed and generated a mixture of oxygen (O2) and hydrogen (H2) or known as oxyhydrogen (HHO) gas via an electrolytic dry cell generator. The HHO was retrofitted experimentally to investigate the engine emissions and exhaust gas temperature from a 1.5 kW gasoline engine. The engine was tested with different power ratings (84–720 W) to investigate the performance and emissions of the engine using gasoline followed by the addition of HHO. The emissions of CO and NOx were measured with different amounts of HHO added. The exhaust temperature was calculated as one of the variables to be considered in relation to pollution. The air-fuel ratios are varied from 12 to 20% in the experiment. The most appropriate air-fuel ratio needed to start the generator with the most environmentally friendly gas emission was analysed. The results showed that the addition of HHO to the engine is successful in reducing fuel consumption up to 8.9%. A higher percentage of HHO added also has improved the emissions and reduced exhaust gas temperature. In this study, the highest quantity of HHO added at 0.15% of the volume fraction reduced CO gas emission by up to 9.41%, NOx gas up to 4.31%, and exhaust gas temperature by up to 2.02%. Generally, adding oxyhydrogen gas has significantly reduced the emissions, and exhaust temperature and provided an eco-friendly environment.

Low emission stepped piston engine for marine outboard motor application

Separating the scavenging process from the lubrication methodology in conventional two-stroke engines is an effective method of reducing emissions. Segregation of scavenging by use of stepped pistons is one such method providing significant improvements in engine durability, and reduced lubricant consumption, together with reduced production cost. The study discusses the approaches used together with those applied to conventional engines. This paper focusses on a marine outboard motor application and cross-comparisons with a comparable four-stroke outboard motor are drawn within the study. One-dimensional computational fluid dynamics models of the engine types have allowed performance and emissions simulations. Where possible, data from experimental dynamometer testing is compared with the theoretical models. A reasonable level of correlation in terms of performance has been observed. Two-stroke cycle engines are able to demonstrate reduced oxides of nitrogen emissions when compared with conventional four-stroke engines. Models of the stepped piston engine have confirmed the lower NOx emission evident with operation on the two-stroke cycle.

Characteristics of Particulate Matter Emissions for Low-Sulfur Heavy Oil Used in Low-Speed Two-Stroke Diesel Engines of Ocean-Going Ships

Characteristics of Particulate Matter Emissions for Low-Sulfur Heavy Oil Used in Low-Speed Two-Stroke Diesel Engines of Ocean-Going Ships

Theoretical model for high-altitude gas exchange process in multi-fuel poppet valves two-stroke aircraft engine

Under the demand of global aviation carbon reduction, the multi-fuel poppet valves two-stroke (MF-PV2S) aircraft engine exhibits advantages such as lower lubricant consumption and the flexibility to high-altitude valve timing adjustment, which position it to play a more significant role in general aviation aircraft and unmanned aerial vehicle propulsion systems. High-altitude gas exchange performance is a critical factor in the thermal efficiency and power characteristics of two-stroke aircraft engines. However, the applicability and accuracy of existing models in predicting the gas exchange process for PV2S engines remain insufficiently discussed. Recognizing discrepancies in the predictions of PV2S gas exchange processes by existing models, a theoretical model applicable to high-altitude gas exchange in an MF-PV2S aircraft engine is established. The modified model adjusts the exhaust composition during the second and third phases of the scavenging process, and a novel model characteristic coefficient, designated as b3, is incorporated to signify the proportion of mixed gas in the exhaust gases at a given moment. Moreover, the model characteristic coefficients b1 and b2, are determined with nonlinearity, based on appropriate relationships that account for the characteristics of the PV2S gas exchange process. The model calculates gas exchange characteristics under different operating conditions and fuels, comparing these results with simulations and tracer gas-based experiments. The findings demonstrate that the model successfully captures the characteristics of early appearance and prolonged duration of fresh charge loss during PV2S gas exchange, significantly enhancing the predictive accuracy. Through adjustments of model coefficients based on specific conditions, the model predicts and describes the variation process of PV2S gas exchange performance parameters under different conditions, including various speeds, different intake-exhaust pressure differences at different altitudes, valve overlaps, and fuel types. The maximum relative errors between model predictions and experimental trapping efficiency, delivery ratio and charging efficiency are 2.58 %, 4.33 %, and 3.89 % respectively. The model can be used for rapid and accurate prediction of gas exchange characteristics under different conditions for the MF-PV2S aircraft engine. Also, it serves as an alternative model of three-dimensional simulation models that can be coupled into the one-dimensional thermodynamic cycle simulation.

Ұқсастық пайдалану шартында екі тактілі қозғалтқышты жасау саласындағы эксперименттік зерттеу

The article applies to similar conditions of use and the creation of a competitive two-stroke engine. Currently, there are prerequisites for creating an effective two-stroke engine, such as direct-flow scavenging, a valve-slotted gas distribution system with a multi-valve mechanism, hydraulic valve control, a diesel cycle with a high compression ratio, etc. To implement a set of promising technical solutions, a design basis is required, on the basis of which a two-stroke engine can be configured. As such, a crank-yoke kinematic mechanism for converting motion was chosen. The mechanism unloads the piston from lateral forces and allows the cylinder to be isolated from the oil sump, using the sub-piston volume as a purge pump. This required the development and research of a cylinder-piston group based on solid lubricant. The sliding bearing has also been improved with improved quality indicators based on the use of thermally conductive and antifriction materials of copper and graphite.

Analysis of scooter engine piston damage

The causes of operational damage to the piston of a single-cylinder two-stroke internal combustion engine (ICE) of a scooter, made of a piston aluminum-silicon alloy by mold casting, were investigated. It was found that the AK21M2.5H2.5 type alloy has a dispersed eutectic structure (α+β-Si) with a small number of primary silicon crystals of a compact shape, the size of which does not exceed 10 μm. The porosity of the cast alloy of the piston is less than the lowest 1st porosity point, as well as the quality structure, could not be the cause of its damage. The average value of the microhardness measured on the surface of the piston head (70 HV0.98) is slightly less than the standardized hardness (90 НВ ÷ 100 НВ) of ingots after mold casting and artificial aging without preliminary hardening, which indirectly indicates overheating of the piston during operation. The detected damage to the outer surface of the piston in the form of deep scratches and worn stripes is not caused by metallurgical or technological factors, but by violations of operating conditions: overheating and lack of lubricant in the contact zone of the piston and cylinder.

Crankcase Explosions in Marine Diesel Engines: A Computational Study of Unvented and Vented Explosions of Lubricating Oil Mist

Accidental crankcase explosions in marine diesel engines are presumably caused by the inflammation of lubricating oil in air followed by flame propagation and pressure buildup. This manuscript deals with the numerical simulation of internal unvented and vented crankcase explosions of lubricating oil mist using the 3D CFD approach for two-phase turbulent reactive flow with finite-rate turbulent/molecular mixing and chemistry. The lubricating oil mist was treated as either monodispersed with a droplet size of 60 μm or polydispersed with a trimodal droplet size distribution (10 μm (10 wt%), 250 μm (10 wt%), and 500 μm (80 wt%)). The mist was partly pre-evaporated with pre-evaporation degrees of 60%, 70%, and 80%. As an example, a typical low-speed two-stroke six-cylinder marine diesel engine was considered. Four possible accidental ignition sites were considered in different linked segments of the crankcase, namely the leakage of hot blow-by gases through the faulty stuffing box, a hot spot on the crankpin bearing, electrostatic discharge in the open space at the A-frame, and a hot spot on the main bearing. Calculations show that the most important parameter affecting the dynamics of crankcase explosion is the pre-evaporation degree of the oil mist, whereas the oil droplet size distribution plays a minor role. The most severe unvented explosion was caused by the hot spot ignition of the oil mist on the main bearing and flame breaking through the windows connecting the crankcase segments. The predicted maximum rate of pressure rise in the crankcase attained 0.6–0.7 bar/s, whereas the apparent turbulent burning velocity attained 7–8 m/s. The rate of heat release attained a value of 13 MW. Explosion venting caused the rate of pressure rise to decrease and become negative. However, vent opening does not lead to an immediate pressure drop in the crankcase: the pressure keeps growing for a certain time and attains a maximum value that can be a factor of 2 higher than the vent opening pressure.

Numerical studies on the flow characteristic of the marine two-stroke engine integrated with the high-pressure exhaust gas recirculation system

The high-pressure exhaust gas recirculation (HP-EGR) has been well-proven for marine engines complying with the IMO Tier Ⅲ NOx regulation. Considering different turbocharged scavenging schemes and emission control modes, intake and exhaust gas management is critical to the HP-EGR design. However, few theoretical studies on it were reported. This paper aims at providing a case study on the flow characteristic of the turbocharged HP-EGR system. With the proposed topology structure of the typical HP-EGR layout, numerical studies on the turbocharged scavenging and EGR design were conducted based on the 6EX340 two-stroke engine. The result showed that the flow characteristic of the turbocharged two-stroke engine can be graphically depicted by simplifying the cylinder and turbine as multi-nozzle in series. According to the nozzle flow equation of uniflow scavenging, there exists an optimum turbine flow area to maximize the scavenging mass flow. Effects of EGR, cylinder bypass, and exhaust gas bypass on the flow characteristic of the two-stroke engine depend on the turbocharger matching. The out-cylinder scavenging and in-cylinder combustion should be optimized interactively to fully explore the fuel economy and NOx trade-off. Finally, the proposed design procedure can provide good guidance for the design and control of the HP-EGR system.

Impacts of Injection Parameters on the Mixture Formation and Performance of Two-Stroke Spark-Ignition Direct-Injection Aviation Kerosene Engine

Abstract Two-stroke spark-ignition engines play a significant role in the field of power sources of small and medium unmanned aerial vehicles. There is a certain transition from burning gasoline to aviation kerosene (or heavy oil) and from carburetor or inlet injection system to direct-injection fuel system. However, the performance of two-stroke spark-ignition direct-injection engines fueled with aviation kerosene was not very ideal under heavy loads. Generally, the mixture formation is very important for engine combustion and performance, while injection parameters have great effects on mixture formation. Thus, various injection parameters of a two-stroke direct-injection kerosene engine were examined here. The results showed too early or too late injection timing (tinj) would deteriorate the mixture formation, resulting in lower brake power and brake thermal efficiency. Here the most suitable tinj was 150 deg CA BTDC. Too high or too low injection pressure (pinj) caused fuel short circuit loss and poor mixture quality, so the optimum pinj was 10 MPa. Too large injector installation angle (β) easily results in fuel spray impingement, and too small β causes fuel short circuit loss. Therefore, the best β was concluded to be 30 deg in this paper.