Apex Seal Research Articles

Computational study of hydrogen injection strategy on the combustion performance of a direct injection rotary engine fueled with natural gas/hydrogen blends

Natural gas/hydrogen blended fuel (NHBF) is considered to be one of the ideal alternative fuels for rotary engine, which can effectively reduce the carbon emission of the rotary engine. The purpose of this paper is to numerically study the influence of hydrogen injection timing (HIT) and hydrogen injection angle (HIA) on mixture formation, flame propagation, and NO emission in the cylinder. In addition, considering that the apex seal leakage (ASL) of rotary engine is difficult to avoid, the NHBF in the cylinder will inevitably leak from the apex seal leakage gap to the adjacent cylinders. Therefore, the NHBF leakage under the action of ASL should be considered. In this paper, a 3D dynamic model of the NHBF rotary engine considering the action of ASL was established. Further, the diffusion and combustion processes of NHBF in the cylinder with different HITs and HIAs were calculated. The results showed that the HIT and HIA can significantly change the flame propagation process by changing the fuel stratification pattern in the cylinder. For improving the combustion efficiency of the engine, the HIA of +45° and HIT of 155°CA (BTDC) adopted by Case:155 + 45 should be set as the hydrogen injection strategy. This is mainly because that for Case: 155 + 45, both natural gas and hydrogen are mainly distributed in the FOC, and the concentration of hydrogen and natural gas near the spark plug is also high. However, the defect of Case:155 + 45 is the significant increase of NO emission.

A comparative study of two embodiments of the limaçon rotary compressor based on theoretical modelling of apex seal dynamics and leakage

As an emerging technology, the limaçon rotary compressor possesses great potential for fluid-processing applications. However, the technology and associated cost required to fabricate the limaçon machine could sometimes be beyond the capability of some manufacturers. To reduce the production cost, circolimaçon embodiment whose rotor and housing are constructed of circular arcs has been proposed. This paper is intended to investigate the viability of the circolimaçon embodiment of limaçon technology based on sealing performance. A nonlinear three-degree of freedom model is presented to describe the dynamic behaviour of the apex seal during the machine operation. Additionally, the leakage through the seal-housing gap is formulated by considering the inertia and viscous effects on the flow. A numerical illustration is offered to compare the performance of the circolimaçon embodiment with that of the limaçon-to-limaçon (L2L) type machine at different pressure ratios and operating speeds. The effect of limaçon aspect ratio on the apex seal dynamics is also investigated. Based on the results, it is found that the circolimaçon embodiment exhibits comparable performance to the L2L-type machine, despite having more significant seal vibrations. The differences in the volumetric and isentropic efficiencies between the two machines are found within 8% and 3%, respectively. Additionally, it is also discovered that the circolimaçon compressor with a small capacity undergoes lower level of seal dynamics, suggesting a better machine reliability.

Modeling and analysis of apex seal leakage in a hydrogen fueled Wankel rotary engine

Under the background of carbon peaking and carbon–neutral, the hydrogen-fueled Wankel rotary engine with excellent power and emission characteristic is under the spotlight. The leakage problem, especially the apex seal leakage, is considered to be an important engineering problem restricting the development of hydrogen-fueled Wankel rotary engine. To make up for research gaps, this study was conducted to investigate the effects of three types of apex seal leakage on engine performance. Two methods for calculating the leakage area of spark plug cavities are proposed and compared, and the definition method based on leakage direction is more consistent with the experimental results. The leading spark plug leakage and corner seal leakage has the greatest impact on peak pressure and IMEP, which reduce the peak value of pressure by 0.249 MPa and 0.047 MPa, and reduce the IMEP by 8.68 % and 10.51 % respectively. In addition to reducing the leakage area, reducing the distance between leading spark plug and minor axis by 5.5 mm could increase the peak pressure by 0.2 MPa and reduce the leakage from the working chamber to the adjacent chambers from 0.055 g to 0.038 g.

Apex seal bottom pressure prediction and leakage analysis of The Hydrogen Fueled Wankel Rotary Engine based on dynamics

The development of hydrogen-fueled Wankel rotary engine is restricted by the leakage problem, especially the apex seal leakage (ASL). In the study, the ASL area is divided into the geometric leakage area (GLA) and the dynamic leakage area (DLA). The models of under-seal pressure prediction and vibration of apex seal are established. The mechanism of GLA and DLA and the effects of key parameters on them are analyzed. Results show that the DLA decreases with the increase of discharge coefficient, clearance between apex seal and slot. There is no DLA when the rotation speed is slower than 2000 rpm or higher than 7000 rpm. Besides, the value of DLA is only 11.23% of GLA and the GLA can be reduced by 88.57% when using a corner-piece structure. The total leakage decreases with the increase of rotation speed. Finally, some measures to reduce the leakage are given.

Numerical study of injection strategy on the combustion process in a peripheral ported rotary engine fueled with natural gas/hydrogen blends under the action of apex seal leakage

To improve the combustion efficiency of the rotary engine fueled with natural gas/hydrogen blends, the effect of the injection strategy of the blended fuel on the combustion process in cylinder was studied. In addition, considering that apex seal leakage (ASL) is difficult to avoid in the actual working process of rotary engines, the action of ASL was considered in the study. Therefore, a 3D dynamic calculation model of a peripheral ported rotary engine considering the ASL was established. Based on the calculation model, the impact of the blended fuel injection position (BFIP) and the blended fuel injection timing (BFIT) on the combustion process was numerically researched. The results showed that when the fuel injection strategy was Case: B-150, whose BFIP was located at the intersection of the cylinder profile and the long axis with the BFIT of 150°CA (BTDC), the blended fuel was more distributed in the front of cylinder (FOC) and the middle of the cylinder (MOC) at the ignition timing, which effectively avoided the problem of the incomplete combustion in the back of the cylinder (BOC). Therefore, to optimize effectively the combustion performance of the rotary engine, the injection strategy of Case: B-150 was recommended in engineering applications.

Evaluation and analysis of injection strategy in a peripheral ported rotary engine fueled with natural gas/hydrogen blends under the action of apex seal leakage

Natural gas/hydrogen blended fuel (NHBF) is considered as one of the most promising alternative fuel for rotary engine. The aim of this paper is therefore to analyse the influence of injection angle (IA) and injection timing (IT) of blended fuel on the combustion performance of a peripheral ported rotary engine fueled with NHBF. Meanwhile, considering that the apex seal leakage is an unavoidable phenomenon during the operation of a rotary engine, the action of the apex seal leakage on flow field and combustion process cannot be ignored. Therefore, a 3D calculation model of the peripheral ported roatry engine, considering the apex seal leakage, was firstly established in this study. Furthermore, under the action of the apex seal leakage, the diffusion and combustion processes of NHBF in the cylinder with different ITs and IAs were calculated. The results indicated that for the distribution of NHBF, when the IT is in the intake stoke, the IA has no obvious effect on the distribution of NHBF. However, when the IT is in the compression stoke, with the increase of IA, the mass of the blended fuel distributed in the back of the cylinder decreases, and the blended fuel continuously accumulates at the middle and front of the cylinder. For combustion process, when the blend fuel injection strategy is Case: 150 + 0, whose installation angle of the blend fuel nozzle is perpendicular to the cylinder block with a IT of 150°CA (BTDC), the blended fuel at spark timing is mainly distributed in the middle and front of the cylinder, which is conducive to the improvement of combustion speed in the cylinder. As a result, compared with other calculation cases, Case: 150 + 0 has the highest combustion speed in the cylinder. Therefore, the IT and IA of Case: 150 + 0 are recommended in the practical engineering application to improve the combustion performace of the peripheral ported rotary engine fueled with NHBF.

Numerical Study on Flow Field in a Peripheral Ported Rotary Engine Under the Action of Apex Seal Leakage

Abstract Apex seal leakage is one of the main defects restricting the performance improvement of rotary engines. The aim of this study is to study the airflow movement in a peripheral ported rotary engine under the action of apex seal leakage. For this purpose, a three-dimensional (3D) dynamic calculation model considering apex seal leakage was first established and verified by particle image velocimetry data. Furthermore, based on the established 3D model, the flow field in the combustion chamber under the four apex seal leakage gaps (0.02, 0.04, 0.06, and 0.08 mms) and the three engine revolution speeds (2000, 3500, and 5000 RPMs) was calculated. By comparing with the flow field under the condition without leakage, the influences of the existence of apex seal leakage on the velocity field, the turbulent kinetic energy, and the volumetric efficiency in the combustion chamber were investigated. Thereinto, the influences of the existence of apex seal leakage on the velocity field is that at the intake stroke, a vortex formed in the middle of the combustion chamber under the condition without apex seal leakage, was intensified by the apex seal leakage action. At the compression stroke, irrespective of the condition with or without apex seal leakage, all vortexes in the combustion chamber are gradually broken into a unidirectional flow. However, there is an obvious “leakage flow area” at the end of combustion chamber due to the existence of apex seal leakage.

Research on the hydrogen injection strategy of a direct injection natural gas/hydrogen rotary engine considering apex seal leakage

The purpose of the present paper is to investigate the hydrogen injection strategy on the combustion performance of a natural gas/hydrogen rotary engine. Considering that apex seal leakage (ASL) is an inevitable problem in the actual working process of a rotary engine, the action of ASL cannot be ignored for an in-depth study of its combustion performance. Therefore, in this paper, a 3D dynamic simulation model that put the effect of ASL into consideration was established. Furthermore, based on the established 3D model, the combustion process of a natural gas/hydrogen rotary engine under various hydrogen injection angle (HIA) and hydrogen injection timing (HIT) was investigated. The results indicated that the hydrogen jet flow first impacted on the rotor wall after entering the cylinder, and then diffused under the action of the vortexes in the cylinder. Therefore, the HIA and HIT could change the hydrogen distribution by changing the hydrogen impact location and the intensities of the vortexes in the cylinder. In addition, the ideal hydrogen distribution at the ignition timing which could improve the combustion efficiency was given. That is, under the premise of ensuring minimized hydrogen leakage, the hydrogen should mainly distribute in the middle and the front of the cylinder, and a high hydrogen concentration is maintained near the spark plug.

Numerical Investigation on the Combustion Performance of a Natural Gas/Hydrogen Dual Fuel Rotary Engine under the Action of Apex Seal Leakage

Direct injection (DI) technology can improve the combustion performance of the rotary engine by realizing the fuel stratification in the cylinder. The purpose of this paper is to numerically invest...

Experimental and Numerical Study on the Formation Mechanism of Flow Field in a Side-Ported Rotary Engine Considering Apex Seal Leakage

Abstract The aim of this research is to investigate the influences of apex seal leakage on the formation mechanism of flow field in a side-ported rotary engine by particle image velocimetry (PIV) and computational fluid dynamics (CFD). In this study, a PIV was used to acquire the two-dimensional (2D) flow field on the rotor housing central plane at an engine speed of 700 rpm. A three-dimensional (3D) dynamic simulation model considering leakage through apex seals was established and verified by the 2D-PIV experiment results. Thereafter, CFD analysis was used to further understand the 3D flow field in combustion chamber under the action of apex seal leakage. The simulation results showed that for the three engine speeds (2000, 3500, and 5000 rpm), in the intake stroke, the vortex generated in the front end of combustion chamber under the condition with no leakage, was strengthened and destroyed by the effects of the small (0.02 mm) and the large (0.08 mm) apex seal leakage gaps, respectively. As the apex seal leakage gap increased, the volume efficiency and the peak pressure decreased continuously. The volume efficiency and the peak pressure caused by any fixed apex seal leakage gap decreased with the increase of the engine speed. Compared with the volumetric efficiency of the condition with no leakage at 2000 and 5000 rpm, the volumetric efficiency of apex seal leakage gap of 0.08 mm decreased only by 24.6% at 5000 rpm, but by 41.2% at 2000 rpm.

Housing Profile Design for Improved Apex Seal Lubrication Using a Finite Length Roller Elastohydrodynamic Lubrication Model

Abstract Finite-length roller contacts are found in apex seal-housing interfaces in rotary engines, as well as in many other mechanical systems, such as those at the interfaces of meshing gear teeth, cam followers, and roller bearings. Rollers are usually designed with crowns and modified ends to mitigate the negative effects of misalignment, thermal deformation, and edge-induced non-uniform displacement. A crowned-roller elastohydrodynamic lubrication model is enriched and employed to investigate seven housing surface profiles, including a sinusoidal recess, sinusoidal ends, the combination design of a sinusoidal recess and sinusoidal ends, multiple sinusoidal recesses, a concave shape, and a concave shape with sinusoidal ends or round corners, aiming to improve the tribological performance of the interface via increasing the minimum film thickness but reducing the average and maximum film thicknesses, and lowering friction coefficient. The modified discrete convolution and fast Fourier transform method with duplicated padding is utilized to deal with the potential free-end-surface effect. The simulation results suggest that the combinations of a concave shape and sinusoidal ends, or round corners, are the best designs because they can help distribute the lubricant most uniformly without causing a negative edge effect.

The formation mechanisms of flow field in a compound intake ported rotary engine considering apex seal leakage

AbstractThe development of rotary engines is severely restricted by its low combustion efficiency and high emission. In‐cylinder flow field is known to play a major role in combustion process for rotary engines. Therefore, in the present article, a three‐dimensional dynamic simulation model considering leakage through apex seals was developed and verified by the two‐dimensional particle image velocimetry experiment results on the rotor housing central plane. Based on the three‐dimensional dynamic simulation model, the formation mechanisms of flow field in a compound intake ported rotary engine under different apex seal leakage gap sizes (0.02, 0.04, 0.06, and 0.08 mms) and engine speeds (2,000, 3,500, and 5,000 rpms) were numerically studied. The simulation results showed that there exist two formation mechanisms of the flow field in the intake stroke, that is, “side intake port dominance” and “peripheral intake port dominance.” For the three engine speeds (2,000, 3,500, and 5,000 rpms), with the increase of apex seal leakage gap size, the formation mechanism of the flow field gradually changed from “side intake port dominance” to “peripheral intake port dominance.” In addition, the influences of apex seal leakage on the volume coefficient and the turbulence kinetic energy in the combustion chamber were also investigated in detail.

Identification of materials and coatings to minimise/eliminate Wankel rotary engine's apex seal/trochoid wear chatter

A well-known problem is existing in Wankel rotary engine that leads the engine to seize before it achieves operational loading conditions. Existing research literature shows one of the primary indications to cause engine seizure are the chatter marks. The present study focuses on performing bench testing to rank the combinations of chosen materials and coatings resulting in lowest friction and reduced chatter. A total combination of 11 materials and coatings were analysed and tested. It was found that titankote with PVD coating and nikasil coating with diamond particles on A-2 tool steel performed the best, resulting in no wear, scuffing or chattering, with an increased surface smoothness. The lowest coefficient of friction measured was 0.06 with HTCS-150 hard trochoid and C-Lee Cook apex seals. The maximum average face wear reduction obtained was 15 μm on titankote with PVD coated trochoid and 18 μm on ceramic apex seal.

A Research of Ti Doped DLC Housing on the Friction Loss in Small Wankel Rotary Engine

Ti doped DLC coating was deposited on ductile iron disk commonly used material in small Wankel rotary engine. The friction coefficient under the working condition of apex seal was investigated. The results show that the Ti doped DLC coating is of low friction coefficient. In addition, the surface hardness and the morphology were improved by Ti doped DLC coating. After that, the Ti doped DLC coating was deposited on the housing. A performance testing platform for small Wankel rotary engine was built. The effect of Ti doped DLC coating under motored and working conditions were measured. The results show that when the operation speed varies from 7 000 to 17 000 r/min, the friction loss between apex seal and Ti doped DLC coating ranges 15~38 W under motored condition. It is only 68% of the friction loss between apex seal and ductile iron. Under working condition, the coating increases 23~78 W of the engine output power, which can improve the output power of small Wankel rotary engine by 24%~43%.

Simulating apex gap sizes in a small scale Wankel expander for air liquefaction

The seals of a Wankel expander produce significant friction and wear, contributing its largest disadvantage. This friction necessitates lubricant to be mixed with the working fluid, increasing the complexity of the device. Removing the seals could therefore produce a significantly more desirable device, if the resulting leakage is acceptable. Currently there are no published studies assessing the performance of a Wankel expander without apex seals, therefore this paper will attempt to address this knowledge gap. A CFD (computational fluid dynamics) model of a Wankel expander without apex seals was developed to assess the performance and leakage amount. Using this model, a parametric study was performed using the apex gap sizes, the rotational speed and the inlet pressure as the variable parameters. Results showed that higher rotational speeds reduced leakage, but resulted in larger pressure drops over the ports, reducing the efficiency. A double-sided ports model helped to counter this, with speeds up to 6000RPM becoming viable. The friction from the apex seals was calculated in order to better compare the cases with and without apex seals. The best efficiency case with apex seals (at 1200RPM, 2 bar inlet pressure) gave 64% isentropic efficiency including apex seal frictional losses. The highest efficiency for the cases without apex seals was 55% (at 6000RPM, 2 bar inlet pressure), however due to the higher rotational speed, the power output was almost four times higher than the case with apex seals above (385 W compared to 100 W).

Effect of DLC coating on the friction power loss between apex seal and housing in small Wankel rotary engine

Abstract The aim of this paper is to study effect of DLC coating on the friction power loss caused by apex seal in small Wankel rotary engine. A numerical model which is capable of evaluating the lubrication state under mixed lubrication is built. The involved parameters of DLC coating are obtained through experiment. Then, the effect of DLC coating is numerically investigated and validated by experimental result. Results show that the friction power loss for DLC coated surface is about 55% of that for uncoated surface. It is partly attributed to the low friction coefficient of DLC coating. Besides, the normal force of asperity is decreased by DLC coating. It is also conducive to the reduction of the power loss.

A Thermal Elastohydrodynamic Lubrication Model for Crowned Rollers and Its Application on Apex Seal–Housing Interfaces

This paper presents a thermal elastohydrodynamic lubrication (EHL) model for analyzing crowned roller lubrication performances under the influence of frictional heating. In this thermal EHL model, the Reynolds equation is solved to obtain the film thickness and pressure results while the energy equation and temperature integration equation are evaluated for the temperature rise in the lubricant and at the surfaces. The discrete convolution fast Fourier transform (DC-FFT) method is utilized to calculate the influence coefficients for both the elastic deformation and the temperature integration equations. The influences of the slide-to-roll ratio (SRR), load, crowning radius, and roller length on the roller lubrication and temperature rise are investigated. The results indicate that the thermal effect becomes significant for the cases with high SRRs or heavy loads. The proposed thermal EHL model is used to study the thermal-tribology behavior of an apex seal–housing interface in a rotary engine, and to assist the design of the apex seal crown geometry. A simplified crown design equation is obtained from the analysis results, validated through comparison with the optimal results calculated using the current crowned-roller thermo-EHL (TEHL) model.

On the apex seal analysis of limaçon positive displacement machines

Rotary machines, and limaçon machines in particular, offer a better power to weight ratio compared to reciprocating machines; however, leakage due to improper apex and side sealing have prevented rotary machines from thriving. In this paper, a modelling approach is presented to analyse the vibration of apex seal during the machine operation and the power loss caused by the seal friction. The seal and spring are modelled as a spring-mass system in which the seal deformation is negligible. The seal-groove relative positions have then been categorised into nine different possible cases based on the number of contact points between the seal and the seal groove. A case study has been presented to demonstrate the reliability of the model.

An analytical investigation of oil film thickness for the apex seal in a small Wankel rotary engine

Abstract The purpose of this paper is to research the oil film thickness between apex seal and epitrochoidal housing in a small Wankel rotary engine. Firstly, a quasi-static equilibrium equation of apex seal is derived with considering interacting forces. It is supposed that oil pressure is the only force supporting the apex seal against other loads. Then, the oil film thickness is evaluated by solving the equilibrium equation and Reynolds equation within a cycle. In addition, the operation speed's influence on the oil film thicknesses is studied. Results indicate that the oil film thickness is a comprehensive parameter affected by many factors, and these factors exert varying degree of influence on the oil film thickness at different positions within a cycle.

Multidisciplinary treatment of a fractured teeth with open apex: apex seal with MTA

Multidisciplinary treatment of a fractured teeth with open apex: apex seal with MTA