Double Swirl Combustion System Research Articles

Effects of combustion chamber diameter on the performance and fuel–air mixing of a double swirl combustion system in a diesel engine

A double swirl combustion system (DSCS) in a diesel engine can make significant efficiency improvements and emission reductions. To explore the effects of combustion chamber diameter on the performance at various operations, DSCSs with a diameter of 83, 91, and 98 mm (DSCS83, DSCS91, and DSCS98) were designed and tested in a single-cylinder diesel engine at the maximum torque speed of 1800 rpm under various loads and various excess air coefficients (φ). The experimental results showed that DSCS83 outperformed the other DSCSs, with a 2.1–4.9% decrease in brake specific fuel consumption (BSFC), 12.4–23.1% reduction in soot, and a shortening of the combustion period by 1.6–3.6 °CA. To reveal the mechanism of fuel–air mixing in different DSCSs, simulation models were established with AVL-Fire. The simulation results indicated that the wall-flow-guiding effects and in-cylinder air motion including air entrainment and reversed squish improved as the combustion chamber diameter decreased, which contributed to fast fuel–air mixing in the outer chamber and the clearance, high indicated power and low soot generation. However, when combustion chamber further decreased from 83 to 76 mm, the unutilized air in the inner chamber and the clearance reduced the performance. An analysis of the uniformity index of the equivalence ratio in different parts of DSCS was performed to characterize the fuel–air mixing process. Results found that DSCS83 had a 1.2–4.8% improvements in the whole-chamber uniformity index at 60° CA ATDC at 32% load operating condition. These results could be an essential reference in the optimization and application of DSCSs in diesel engines.

Effects of Combustion Chamber Diameter on the Performance and Fuel-Air Mixing of a Double Swirl Combustion System in a Diesel Engine

Effects of Combustion Chamber Diameter on the Performance and Fuel-Air Mixing of a Double Swirl Combustion System in a Diesel Engine

Combustion performance and mechanisms of the fuel/air mixture in a new separated swirl combustion system

To improve air efficiency in the combustion chamber, a new separated swirl combustion system (SSCS) was developed and is proposed herein. The SSCS performance was validated against a double swirl combustion system (DSCS) in an experimental test with a single-cylinder diesel engine. The experiment results show that the SSCS effectively reduces fuel consumption and soot emission, with a maximum decrease in fuel consumption of 5.41% (when the effective power was 17 kW) and a maximum decrease in soot emission of 20.48% (when the effective power was 43 kW). Then, simulation was used to investigate and reveal the mechanisms behind the fuel/air mixture in the chamber. The simulation results show that the angular fuel sprays collide with the unique circular ridges in the SSCS, which improves air utilization in the chamber and accelerates the fuel/air mixture, reducing soot emission.

Soot formation and oxidation mechanisms in a diesel engine separated swirl combustion system

The separated swirl combustion system (SSCS) is a new combustion system developed to improve fuel efficiency and reduce soot emissions in diesel engines. While soot emissions from the SSCS can be tested in a real-world single-cylinder engine, soot formation and oxidation cannot be; therefore, the mechanisms behind those processes have not yet been researched. To understand the mechanisms of soot formation and oxidation in the SSCS, soot evolution must be investigated using a simulation model. To bridge this gap, this study analyzed the combustion and emission performance of the SSCS under different speeds in a real-world single-cylinder engine. Then, a new phenomenological model was developed and used to simulate soot formation and oxidation and reveal the mechanisms behind those processes. The SSCS with the new model was validated against a double swirl combustion system (DSCS). The experiment results show that at 2100 r/min, the SSCS significantly reduced fuel consumption (about 6.54 g/(kW h)) and soot emission (0.17 FSN) by 2.89% and 6.31%, respectively. The simulation results show that the DSCS generates more incipient soot particles and soot mass than the SSCS, and surface soot oxidation is faster in the SSCS. The mechanisms analysis shows that the equivalence ratio is smaller in the SSCS than in the DSCS, so fewer incipient soot particles are generated, and the temperature is higher, which speeds up soot oxidation. Furthermore, the combustion duration is much shorter in the SSCS than in the DSCS, which means that the time between the end of combustion and the exhaust valve opening is longer, granting more time for soot oxidation. Due to the decreased soot formation and faster soot oxidation, the soot mass is also lower in the SSCS than in the DSCS.

Effects of separated swirl combustion chamber geometries on the combustion and emission characteristics of DI diesel engines

To improve air efficiency in the combustion chamber, a new separated swirl combustion system (SSCS) is proposed in this study. The combustion performance and emission characteristics were analyzed using three-dimensional simulation. A sensitivity analysis of indicated power and soot emission by chamber geometries was carried out. Based on the results of the sensitivity analysis, the chamber geometries were optimized. Then, the combustion and emission performance of the SSCS with optimized chamber geometries under different speeds was tested and compared with a double swirl combustion system (DSCS) in a single-cylinder diesel engine. The simulation results show that because the angle of the inner chamber affects the fuel distribution in the inner and outer chamber, it has the greatest influence on the SSCS combustion performance. The depth of the separated chamber is the second most important optimization parameter, followed by the diameter of the outer chamber, the separated chamber diameter, the angle of the outer chamber and finally the volume ratio of the inner and outer chamber. By comparing the combustion performance, fuel/air mixture, velocity distribution and soot emission in the cylinder of different SSCS chamber geometries, the optimized chamber geometries were determined. Then, the combustion and emission performance of the SSCS with optimized chamber geometries was compared with a DSCS combustion system. The results show that the brake-specific fuel consumption (BSFC) was lower and the indicated thermal efficiency was higher in the SSCS than in the DSCS at various engine speeds. The results of this study are of great significance for the optimization of chamber geometries as well as the improvement of fuel/air mixture and combustion performance.

Fuel and air mixing characteristics of wall-flow-guided combustion systems under a low excess air ratio condition in direct injection diesel engines

In this study, wall-flow-guided combustion systems (WFGCS) were analyzed with the view to improve air use efficiency, fuel economy and emission performance in direct injection (DI) diesel engines. The results of previous study show that WFGCS facilitate favorable combustion and emission performance at low excess air coefficients. To quantitatively analyze the fuel/air mixing characteristics of WFGCS under a low excess air ratio, a computational fluid dynamics (CFD) simulation method was used to measure the spray concentration distribution in a double-swirl combustion system (DSCS), lateral-swirl combustion system (LSCS) and ω combustion system (OMECS). The results show that with an excess air ratio of 1.5, WFGCS reduce the proportion of the rich mixture with an equivalence ratio between 2 and 4 and increase the combustible mixture with an equivalence ratio between 1 and 2, which is conducive to improving the combustion and emission characteristics of DI diesel engines. Therefore, WFGCS have broad application prospects in refining the fuel/air mixture and improving the air use efficiency in the combustion chamber of DI diesel engines.

The wall-flow-guided and interferential interactions of the lateral swirl combustion system for improving the fuel/air mixing and combustion performance in DI diesel engines

The lateral swirl combustion system was designed based on and to improve upon the traditional ω-type combustion system. Previous research has verified the outstanding combustion performance of the lateral swirl combustion system. In this study, to reveal the interaction mechanisms between the lateral swirl combustion chamber and spray jets, experimental and numerical study was conducted at various spray incident angles (φ) where the relations between the combustion chamber and spray jets are different. The spray impinging processes and combustion performance were measured in a single-cylinder diesel engine with an endoscopic system. The distribution of velocity and the equivalence ratio was analyzed through simulation. Then, under the optimal φ, the fuel/air mixing quality and combustion performance was verified in comparison with a double swirl combustion system.The results show that fuel consumption and soot emissions of the lateral swirl combustion system decreased with an increasing spray incident angle. When φ reached its maximum, the combustion system exerted the best combustion performance, because the wall-flow-guided interaction between the chamber and spray jets and the interferential interaction from the neighboring wall jets were optimized. This combined effect promoted in-cylinder fuel/air mixing and combustion. Under this circumstance, the indicated thermal efficiency of the lateral swirl combustion system increased by 3.4–6.8% compared with the double swirl combustion system, and the soot emissions decreased in the ranges of 45–73%. It was concluded that the lateral swirl combustion system with a maximum spray incident angle significantly improves the combustion performance of DI diesel engines due to the wall-flow-guided and interferential interactions between the combustion chamber and spray jets. These findings are key to the design and development of a high-efficiency lateral swirl combustion system for DI diesel engines.

Research on energy distributions of the lateral swirl combustion system in DI diesel engines

The lateral swirl combustion system (LSCS) can improve the air-use, fuel and emission performance of direct injection (DI) diesel engines. In this study, the differences in energy distributions between the LSCS and the double swirl combustion system (DSCS) were analyzed under different working conditions using a single-cylinder test system. A simulation calculation was used to compare the velocity, mixture equivalence ratio and in-cylinder temperature distributions of the working medium in the two combustion chambers, elucidating the different energy distributions of the two chambers. Additionally, a new idea is proposed herein for the design of LHR engines. The experimental results show that, compared with the DSCS under different operating speeds (1300–2100 r/min) and different loads (21–43 kW), the indicated thermal efficiency of the LSCS was approximately 2% higher, the percentage of the exhaust energy and heat transfer to the total energy was approximately 2% lower, the cylinder head temperature was 2–20.5 K lower, the ratio of the cylinder head heat transfer to the total heat transfer was 2–8% smaller and the heat transferred to the cooling water in the water jacket of the cylinder head was 0.2–1 kW lower. The in-cylinder velocity distribution, mixture equivalence ratio and temperature distribution of both the LSCS and the DSCS were compared through simulation. The results show that the fuel in the LSCS developed along the wall of the combustion chamber circumferentially due to the convex edge, and the high temperature zone distributed along the circumference of the combustion chamber. In the DSCS, most of the fuel moved to the cylinder head due to the circular ridge, and the high temperature zone existed near the cylinder head. The LSCS had a lower cylinder head temperature, a higher exhaust gas temperature, and less heat transferred to the cooling water through the cylinder head. Therefore, the unique shape of the LSCS chamber guided the movement of the fuel and reduced the concentration of the fuel/air mixture near the cylinder head, which reduced the heat transferred to the cooling system through the cylinder head and improved the thermal efficiency. In addition to these findings, this study also provides a foundation for the design of a low heat rejection engine.

Effects of lateral swirl combustion chamber geometries on the combustion and emission characteristics of DI diesel engines and a matching method for the combustion chamber geometry

Previous experimental results show that a lateral swirl combustion system (LSCS) significantly improves the fuel consumption and the soot emission in direct injection (DI) diesel engines. To further improve LSCS performance and effectiveness, this study undertook numerical simulation to analyze the effects of the LSCS chamber geometries on combustion and emission characteristics under the condition of 2500 r/min and full load, revealing the relevant influence mechanisms. Based on a sensitivity analysis on the indicated power, the chamber geometry optimization was accomplished. The performance improvement of the optimized LSCS was verified using a single-cylinder DI engine. However, due to the interplay between fuel spray jets and wall surfaces, the optimized results are different for various fuel supply systems. To apply the LSCS effectively in different fuel supply systems, a matching method for LSCS chamber geometry is proposed in this paper.The results show that the combustion performance of the LSCS is primarily affected by the geometries of the split-flow creation, in which θ (the deviation angle of flow-guide) plays a dominant role. When θ was in the range of 15–27°, the combustion chamber created favorable flow guidance for spray and promoted the fuel/air mixture formation. After the geometrical optimization of the LSCS, fuel consumption decreased by 2.8–4.1 g/(kW.h) and soot emission decreased by 69–75% under various engine speeds as compared with the double swirl combustion system (DSCS).

The combustion and emission characteristics of a multi-swirl combustion system in a DI diesel engine

In this study, the authors developed a new multi-swirl combustion system (MSCS) and investigated its combustion and emission characteristics. The MSCS combines the structural features of a double swirl combustion system (DSCS) and a lateral swirl combustion system (LSCS) and utilizes the arc structure of the MSCS to lead fuel to (1) form multi-swirls in both a longitudinal and lateral direction, (2) accelerate the fuel/air mixture and (3) improve the combustion process in a diesel engine. An experimental study and simulation analysis was used to verify the MSCS combustion and emission characteristics. In the experimental study, tests at various speeds were conducted using a single-cylinder diesel engine. The experimental results, including the brake specific fuel consumption (BSFC), soot emission, NOx emission and in-cylinder pressure were recorded and compared with results from a DSCS that was operated under the same condition. In the simulation, the fuel spray process was studied using AVL-Fire. The fuel velocity profile and the fuel/air equivalent ratio distribution were studied to verify the formation of multi-swirling fuel in the combustion chamber. The experimental results show that the BSFC of the MSCS was lower by 4–5g/(kWh), and the soot emission was lower by about 60% in comparison to the results from the DSCS. The simulation results show that the fuel formed two longitudinal swirls in opposite directions after touching the circular ridge, and the fuel in the outer chamber formed two swirls in lateral space after touching the convex edge. This multi-swirl enlarged the diffusion space of the fuel in both the inner and outer combustion chamber and accelerated the formation of the fuel/air mixture, which led to a decrease in soot emission and fuel consumption from the MSCS.

Combustion and emission performance of a split injection diesel engine in a double swirl combustion system

The authors developed and tested a split injection strategy in a double swirl combustion system (DSCS). Different split injection strategies with different ratios of pilot injection fuel to total fuel mass (herein defined as “pilot injection/fuel mass ratios”) and dwell times were compared with an optimized single injection strategy in terms of the break specific fuel consumption (BSFC). The in-cylinder pressure, heat release rate and in-cylinder temperature were analyzed to explore the in-cylinder combustion process. The NOx emission was also measured. With the total fuel mass being 100 mg/cycle and excess air coefficient being 2 at 2100 r/min at a 5% pilot injection/fuel mass ratio and a 10 deg dwell time, the BSFC decreased by 2.7% compared with the single injection strategy. The NOx emission increased from 940 ppm to 1140 ppm. An ‘acceleration effect’ helped the DSCS when dwell time was short. A spray visualization experiment and numerical simulations were carried out to explain these phenomena. It is concluded that the split injection condition with a smaller pilot injection/fuel mass ratio and a shorter dwell time performed better than the single injection condition in terms of the thermo-atmosphere utilization, space utilization and acceleration effect.

Combustion and emission characteristics of a lateral swirl combustion system for DI diesel engines under low excess air ratio conditions

In order to improve the utilization of air in the cylinder, decrease the thermal load and improve the emission performance of diesel engines, a new lateral swirl combustion system (LSCS) has been proposed in this study. An experimental investigation of the LSCS at various excess air ratios was conducted using a 132mm single-cylinder direct injection (DI) engine. The experimental results indicate that, compared to a double swirl combustion system (DSCS), the LSCS achieves better fuel consumption and lower soot emissions. The fuel consumption was decreased by 4–5g/(kWh) at each excess air ratio, corresponding to a reduction of about 1.13–2.8%. The decreasing trend of soot formation was also clear, with a significant reduction in the range of 63.4–70.8%. The LSCS also showed excellent performance under an excess air ratio of 1.3–1.6. At an excess air ratio of 1.3, the brake-specific fuel consumption (BSFC) of the LSCS was 228g/(kWh), the soot emission level was 1.1 Filter Smoke Number (FSN) and the exhaust temperature was about 560°C. Related numerical research on the impact of in-cylinder fuel/air equivalence ratio, in-cylinder temperature and in-cylinder velocity of the DSCS and the LSCS was performed, and the results show that a large proportion of the fuel/air diffusion was at the bottom of the chamber in the LSCS (away from the cylinder head). The lower concentration of the fuel/air mixture near the cylinder head in the LSCS had a positive effect and reduced the thermal load so that less engine heat was taken away by the cooling water in the water jacket of the cylinder head. Due to the lower thermal load and higher efficiency, the exhaust temperature of the LSCS was higher than that of the DSCS. The higher exhaust temperature had a positive influence on soot oxidation, which caused the soot decrease in the LSCS. It is suggested that the LSCS, with its excellent fuel consumption and low soot emission, has better application prospects in diesel engines, than the DSCS under a low excess air ratio.

Experimental research on the diffusion flame formation and combustion performance of forced swirl combustion system for DI diesel engines

In order to optimize the fuel/air mixture formation and decrease pollutant emissions of direct injection (DI) diesel engines, a new concept of forced swirl combustion system (FSCS) included double swirl combustion system (DSCS) and lateral swirl combustion system (LSCS) was proposed and implemented by a unique design of the geometric shape of the combustion chamber. Related numerical research on combustion and emission characteristics of this new system was conducted and acceptable numerical simulation results about its feasibility were drawn initially. To make a better understanding of the mechanism of fuel/air mixture formation in FSCS, visualization of diffusive flame was conducted in a constant volume vessel. The flame images were captured by a high speed camera and the image results indicated that, compared with the traditional omega combustion system (OMECS), both of the flame spread space and spread area of FSCS were increased after the spray impingement. Then, fuel economy and emission performance of FSCS were tested in a single cylinder engine to evaluate its application in diesel combustion system. Test results shown that the LSCS could achieve a better fuel consumption and less soot emission property than DSCS. Both of the two combustion systems (LSCS and DSCS) have the promising benefit in fuel consumption and soot emission compared to OMECS. It is suggested that the fuel/air mixing and engine performance could be promoted in FSCS owing to the introduction of swirling combustion.

Emission characteristics of double swirl combustion system in diesel engine

Emission characteristics of double swirl combustion system in diesel engine

Research and Development of Double Swirl Combustion System for a DI Diesel Engine

In order to make full use of the air in the chamber, improve the mixing process, and reduce raw emissions and fuel consumption of diesel engine, we introduce the the concept of a new combustion system—the Double Swirl Combustion System (DSCS)—and introduce their hypothesis regarding the fuel-air mixing mechanism under DSCS. For validating the hypothesis, we made a series of actual diesel engine tests on DSCS. The engine tests were based on a 150-mm diesel engine, and both single-cylinder and multicylinder engines were tested under natural aspirated intake condition and boost intake condition. The results indicate that DSCS is suitable for improving a big bore diesel engine. Later, we made a series of spray experimental researches in order to investigate DSCS and whether it can be used under different load conditions. In addition, we investigated how the structural parameters of the DS chamber affect the fuel-air mixing process in order to establish an optimum design method of the DS chamber. In order to verify whether DSCS can be used in different types of diesel engines, we made a series of engine tests on a 132-mm diesel engine. Results indicated that DSCS also can present a wonderful performance on medium bore diesel engine. For phenomena of 150- and 132-mm diesel engines' performance by matched DSCS, we suppose there exists necessary to make a further research on DSCS from the microcosmic level. Therefore, we made a series of simulations on 132-mm DS and the 132-mm original chambers. From the simulation results, they obtained meaningful results from the velocity field and temperature distribution comparisons. The results we obtained validate that DSCS has many advantages, such as a diesel engine with an ideal heat release rate, a better fuel economy, a lower emission, and a lower thermal load, all showing potential and a bright future for DSCS owing to the wide application of electronic-controlled fuel injection systems.