journal of computing and electronic information management ... · journal of computing and...

Journal of Computing and Electronic Information Management

ISSN: 2413-1660

56

Design and analysis of Air-powered Rotary Engine

Di Zou a, Gongxiang Zhong b

MOE Key Laboratory of Oil & Gas Equipment, Southwest Petroleum University, Sichuan

Chengdu 610500, China

[email protected], [email protected]

Abstract: In view of the phenomenon that the pressure energy of natural gas is

wasted in the process of using the Downhole Throttling technology in the high pressure

well, the idea of using the air-powered rotary engine to transform natural gas pressure

energy into mechanical energy to drive the generator is put forward. Based on the

structural feature of traditional Wankel-type rotary engines the overall structural

design calculations of a new air-powered rotary engine are carried out and a new

decompression scheme is set up, and the flow field simulation is performed using

advanced CFD numerical simulation methods. According to simulation data the

correctness of the design calculation of the first stage rotary engine is verified and the

structural defect improvement basis of the second rotary engine is provided. The

problem of hydrate generation in the cylinder is solved when the second stage air inlet

temperature is increased from 343K to 353K. A new set of precise air-powered rotary

engine FLUENT simulation scheme was proposed and a new set of ideas of the

research on air-powered rotary engine is provided.

Keywords: CFD, FLUENT, air-powered rotary engine, dynamic mesh, numerical

simulation.

1. Introduction

The outlet pressure of natural gas well is between 20 and 100MPa and meanwhile the

pressure of pipeline is between 6 and 10Mpa[1]. Thus the throttle device is set to

decreases the gas pressure from well till the pipeline networks allowed.

However the throttle process wastes the energy from the high pressure from natural

gas in the field of oil and gas development. A simple calculation can demonstrates that

the high pressure natural gas contains plenty of energy which can be quite valuable in

economical and practical area by proper using[2].

The main use of natural gas pressure energy is electric generation and refrigeration.

The foreign scholars research the electric generation by pressure energy of natural gas

Volume 5 Issue 7 2018

57

and get some results[4-9]. The air-powered engine was refitted by the rotary engine

invented by Felix Wankel. However, because of the blockade on technique, few of

relative information can be gained.

A system of air-powered engine which follows the Rankine cycle performs better in low

power output. A scheme of refitting the rotary engine to air-powered engine is put

forward. The scheme remains the superiority of rotary engine about low-vibration,

small volume and continues working which drives much scholars research on that. But

an important disadvantage of rotary engine that compares with the combustion

efficiency of reciprocating internal combustion engine, the air-powered rotary engine

performs poor because of the low compression ratio which leads the high consumption

and heavy pollution. Those disadvantages are not been avoided till now.

2.The Physical Design of Air-powered Rotary Engine

Air-powered rotary engine consists of rotor, end cap, cylinder block and bent axel etc.

In the paper a air-powered rotary engine applies to natural gas well in high pressure

difference, high rotation speed and mass flow working condition based on the existing

result of rotary engine[14,15].

2.1 The Theory Introduction of Air-powered Rotary Engine

The object line of cylinder block of air-powered rotary engine is double arc short-range

cycloid, the object line of rotor is the inner envelope of the object line of cylinder block.

An offset e exists between the center of cylinder block and rotor.

The inner gear of rotor and outer gear of end cap keeps engage which the gear ratio is

3:2. The cylinder block is treat as a stator as a fixed end, the rotor moves eccentrically

drives by eccentric bent axel. The 3 peaks of rotor slide on the inner wall of cylinder

block which separates the working chamber into 3 parts as air intake, inflation and air

outtake(Fig.1)[16]. Fig.2 shows the volume changing of working chamber by the

rotation of bent axel.

Fig.1 The physical design of air-powered rotary engine


58

Fig.2 The relationship between the volume of 1st working chamber and the angel of

bent axel

2.2 The Scheme Design of Depressurization

A 2-class depressurization scheme is selected, and the designed parameters is showed

as:

(1)40MPa to 18MPa in the first class depressurization, 18MPa to 8MPa in the second

class depressurization.

(2)The initial temperature of 40MPa natural gas is 80℃;

(3)The flow of natural gas is 80× 104m3/d(standard condition);

(4)The rotation speed of bent axel is 3000r/min;

(5)The pure methane is selected as working fluid which the density is

0.717kg/m3(standard condition).

Because of the clearance volume while engine working, the exhaust coefficient is

introduced as dλ :

lTd (1)

λ is pressure coefficient; Tλ is temperature coefficient; lλ is leakage coefficient.

Table 1 The exhaust coefficient of each class cylinder block

calss Ⅰ Ⅱ

λ 0.98 0.99

Tλ 0.95 0.96

lλ 0.97 0.98

lTd 0.91 0.93

The exhaust gas temperature after depressurization is given by:

kk

sd TT1

1

(2)

dT is exhaust gas temperature; sT is intake air temperature; 1 is pressure drop ratio.

The 1st exhaust gas temperature is 293.6K after calculation. The aquo-complex will not

generate based on Fig.3[17].


59

Fig.3 The pressure-temperature curves of methane aquo-complex generation

The temperature is decreased to 20.6 after 1st depressurization. To make sure that the

aquo-complex won’t generate after 2nd depressurization, the gas is heated to 70; The

1st exhaust gas temperature is 285K. The aquo-complex will not generate based on

Fig.3.

2.3 The calculation of structural design

The inner object line (epicycloid) can be written as:

3

3

sinsin

coscos

Rey

ReX (3)

In (3), R is generating radius; e is offset.

The object line of Wankel rotor is the inner envelope of epicycloid of cylinder block

which can be written as:

21

2

2

21

2

2

3sin1sin5sin

4sin8sin2sin

3sin1cos5cos

4cos8cos2cos

29

2

3

29

2

3

vvve

vvvRX

vvve

vvvRX

Re

Re

Re

Re

(4)

In (4), 12v ,

6

21

6

19

6

13

6

11

6

5

2，，，，， ππππππv 。

The main dimension of the first and second class air-powered engine is given in table

2.


60

Table 2 The dimension parameters of air-powered rotary engine

object First class Second class

Generating radius(mm) 78 90

offset(mm) 13 15

Width of rotor and cylinder block(mm) 37 45

Thickness of cylinder block(mm) 20 20

Diameter of bend axel eccentric disc(mm) 65 75

Spindle diameter of bent axel(mm) 35 41

3 The simulation of air-powered rotary engine based on FLUENT

3.1 The geometric model construction of air-powered rotary engine

A simplified 3D model of air-powered rotary engine based on SolidWorks is given:

Fig.4 The 3D model of 1st and 2nd class rotor

3.2 The construction of channel model and meshing

Lead the 3D model of air-powered rotary engine into the DM module of Workbench and

the channel model is constructed and processed, and the 2D section model of 3D

channel is generated; Because of the contact relation between the rotor peak and inner

wall of cylinder block, the rotor size is narrowed 0.99 times to gain a 0.65mm,0.85mm

gap between the 1st and 2nd rotor and cylinder block (showed as Fig. 5a), the following

simulation setting uses a “cotton plug” method to solve the leak problem of the gaps._

4 definitions is added in cyl fluid in UDF to define the 3 peaks of rotor in cyl fluid, and

the flow resistance is added to its both sides to avoid the leak from the gaps; The

pressure cloud diagram is showed in Fig.5b about after setting the “cotton plug” which

demonstrates no air leaking in the situation of high pressure difference between each

cylinder blocks and gaps existence.


61

(a) Reserved gap (b)The pressure cloud diagram after setting “cotton plug”

Fig.5 The setting of “cotton plug”

The type of mesh is non-structural triangular mesh which its size is 1mm showed as

Fig.6, and the mesh number is 25010,34024. The update of dynamic meshing is

achieved by Smoothing Layering and Remshing method.

Fig.6 The meshing in GAMBIT

While setting the boundary condition, the “valve” is set to air inlet and outlet with a 5

time control which is set by Define Event.

The transient solving method is chosen and the k-ε model is chosen for analyzing the

turbulence situation[18]. The control equation is given as:

0

dAnpvdxdydxAvt

(5)

the first item of left side of (5) is the control of mass increment, the second item is the

net flow from control surface to control volume. A is control surface, V is control

bolume

The moment conservation equation is given as:

z

p

y

p

x

pzdt

du

z

p

y

p

x

pydt

dv

z

p

y

p

x

pxdt

du

zxyxxx

zxyxxx

zxyxxx

F

F

F

(6)


62

In (6), xF , yF , yF is the mass force component of unit mass fluid of x,y,z direction, P is

the internal stress tensor of fluid.

The energy reservation equation is given as:

2

21

11

1

up

heffijijjjxeffx

ixt

hE

SuJhk

pEuE

T

(7)

In (7), is the effective index of heat conduction, is the diffusion flux of component j, is

the volume heat source.

The PISO algorithm is chosen for calculation and the type of pressure discretization is

PRWESTO! method.

3.3 The result and analysis of simulation of air-powered rotary engine

The simulation time is 15ms because of the exhaust time is 15ms; The simulation

verified whether the pressure and temperature variation of air-powered engine in the

process of air suction and inflation can fit the design calculation. The pressure cloud

diagram and pressure-time variation curve is given as:

(a)Gas intake completion time (b)Gas exhaust time

The pressure cloud diagram of 1st class air-powered engine

(a)Gas intake completion time (b)Gas exhaust time

The pressure cloud diagram of 2nd class air-powered engine


63

The pressure-time variation curve of 1st/2nd class air-powered engine

Fig.7 The simulation results of 2 class air-powered engine pressure

The gas pressure of inlet is 40MPa, the average pressure of inlet cavity is 39.92MPa and

its volume is 150.1cm3 after the gas intake completion and the bent axel rotates

170°(t=9.4ms) from initial position; then the intake cavity pressure drop to 19.4MPa

while the cavity pressure is 208.3cm3 after the bent axel rotates 270 (t=15ms) which

the inflation and pressure decrease completes; the deviation between design pressure

drop and simulation is 7.7% which within the tolerance interval, the first class pressure

drop is proved.

The gas pressure of inlet is 18MPa, the average pressure of inlet cavity is 17.92MPa and

its volume is 253.3cm3 after the gas intake completion and the bent axel rotates

143°(t=7.94ms) from initial position; then the intake cavity pressure drop to 7.52MPa

while the cavity pressure is 439.1cm3 after the bent axel rotates 270 (t=15ms) which

the inflation and pressure decrease completes; the deviation between design pressure

drop and simulation is 6.6% which within the tolerance interval, the second class

pressure drop is proved.

The temperature and temperature –time variation curve is showed in Fig.8. The first

class gas intake temperature of air-powered rotary engine is 353K, the cavity average

temperature after gas intake completion is 346.5K, and the gas exhaust temperature

drops to 298K after inflation completion while no aquo-complex generating and the

deviation value is acceptable, so the first class temperature drop is proved.

Gas intake completion time Gas exhaust time


64

The temperature cloud diagram of 1st class air-powered engine

Gas intake completion time Gas exhaust time

The temperature cloud diagram of 2nd class air-powered engine

The temerature-time variation curve of 1st/2nd class air-powered engine

Fig.8 The simulation results of 2 class air-powered engine pressure

The second class inlet temperature of air-powered rotary engine is 343K, the cavity

average temperature after gas intake completion is 338.5 based on simulation results,

the exhaust gas temperature is drops to 273.3K after inflation completion which is

lower than design temperature 285K, so the second class design is inacceptable which

needs improvement.

3.4 The structural improvement based on flow field simulation of FLUWENT

Considering the problem of the temperature drop leads the aquo-complex generation,

the temperature is raised to 353K from 343K of gas inlet of the second class

air-powered rotary engine. The optimized parameters of second class air-powered

rotary engine is showed in table 3.


65

The contrast between the original and improved parameters

Object Original design Optimized

design

Generation radius(mm) 90 90

Offset(mm) 15 15

Width of cylinder block and rotor(mm)(optimized)

45 47

Thickness of cylinder block(mm) 20 20

Diameter of bend axel eccentric disc(mm) 75 75

Spindle diameter of bent axel(mm) 41 41

Gas pressure of intake/exhaust(MPa) 18MPa,8MPa 18MPa,8MPa

Gas temperature of intake/exhaust((K)(optimized)

343K,285K 353K,292.6K

Bent axel angle of gas intake/exhaust (optimized)

intake：143°

exhaust：270°

intake：138.2°

exhasut：260°

Time switch of intake and exhaust “valve” (ms)(optimized)

Intake "valve” closes：7.94ms

Exhaust “valve” opens：15ms

Intake "valve” closes：：

7.67ms Exhaust “valve” opens：

14.45ms

The optimized gas pressure of inlet is 18MPa, the average pressure of inlet cavity is

17.93MPa and its volume is 190.5cm3 after the gas intake completion and the bent axel

rotates 138.2°(t=7.67ms) from initial position; then the intake cavity pressure drop to

7.71MPa while the cavity pressure is 342.8cm3 after the bent axel rotates 260

(t=14.45ms) which the inflation and pressure decrease completes; the deviation

between design pressure drop and simulation is 3.62% which within the tolerance

interval, the second class pressure drop is proved. The optimized second class

presswure-time variation curve is showed in Fig.9a:

(a)Pressure-time (b)Temperature-time

Fig.9 The optimized 2nd class pressure/temperature-time variation curves


66

The optimized temperature of gas inlet of air-powered rotary engine is 353K which the

temperature –time variation curve is showed in Fig.9b. The average cavity temperature

after gas intake completion is 347.5K, the temperature drops to 282.3K after inflation.

Though the temperature is still lower than the design value, aquo-complex will not

generate based on Fig.3 and the deviation is acceptable. The optimization and

improvement solves the problem of aquo-complex generation.

4. Conclusion

(1)A depressurization scheme and structure design is given of 40MPa pressure of

natural gas wellhead of 2 classes air-powered rotary engine, 1st class design is verified

by FLUENT dynamic mesh flux field simulation; the problem of aquo-complex

generation is solved by elevating the temperature of 2nd class inlet from 343K to 353K.

(2)The “cotton plug”, ”valve”, ”UDF” method is used to solved the problem of

simulating the special flux field air-powered rotary engine, a novel and precise

simulation method of air-powered rotary engine is put forward.

References

[1] ZHONG Gong-xiang, LIU Jing-wei, LV Zhi-zhong, et al. A kind of wellhead natural gas power generation system [P], China: CN103306761A,13-9-18.

[2] DIAO An-na, XU Qiong-yan, ZHANG Quan-ming, et al. Development and application of natural gas screw expander[J]. Chemical Engineering of Oil and Gas, 2013,42(04):378-381.

[3] YANG Hui-feng, LIANG Hai-ping, WANG Lin-ping, et al. Technology and development status of natural gas residual pressure utilization[J]. Energy Conservation in Petroleum & Petrochemical Industry, 2017,7(11):15-18+9.

[4] ZHANG Hui, LI Xia-xi, XU Wen-dong, et al. Research on cooling and power generation system using excess pressure from natural gas high-pressure network[J]. Gas & Heat, 2015,35(07):35-37.

[5] Vasiljev vladimir yaroslavovich (ru),Kiselev oleg mikhailovich (de). Method of Utilization of Gas Expansion Energy and Utilization Power Installation for Implementation of This Method: US A.US20090272115A1. Nov. 5, 2009.

[6] SHEN D M, FERNANDES F, SIMQES-MOREIRA J R.Using gas pipeline pressure to liquefynatural gas or generate electricity [J]. Hydrocarbon Processing, 2006, 85(1): 47-50.

[7] Sasaki, Yozo. The state of the TRT[C]Proceedings of Energy Saving at Steel Plant. Beijing: Metallurgy Industry Press, 1982: 104.

[8] HAN Yu-jing,CAO Yong-jie,TAO You-zhi.Process optimization and productive practice of Shougang Jingtang No.1 blast furnace[J].Metallurgical Power, 2010(4):20.

[9] ZHU Ren-liang, WANG Tian-qiu, WANG Xun-fu. Blast furnace optimization operation and lowcarbon production[J]. China Metallurgy, 2013, 23(1): 30.

[10] WANG Yun, LIU Xiao-yong, ZHOU Yong.Design and Performance Analysis of a Triangle Rotary Piston Air-powered Engine[J]. Mechanical Science and Technology


67

for Aerospace Engineering Journal of Northeastern University, 2009,28 (07): 950- 954+959.

[11] DONG Jing-hui.Triangulation rotor pump [J]. Chemical and General Machinery, 1980(11):19-26.

[12] Badr,O,Naik,S,.O’Callaghan,etal.Rotary Wankel engines as expansion devices in steam Rankine-cycle systems.Appl.En.,39(1)(1991)59-76.

[13] ZHENG Jing-hui, SUN Xuan, YANG Can-jun.Design and experimental research of pneumatic micro-rotary engine[J]. Machine Tool & Hydraulics | Mach Tool Hydrau, 2006,12:101-104+126.

[14] PAN Jian-feng, CHEN Rui, FAN Bao-wei, et al. Numerical simulation of combustion process in LPG rotary engine[J]. Journal of Thermal Science and Technology, 2013,12(3): 242-248.

[15] Fan Bao Wei, Pan Jian Feng, Liu Yang Xian, Chen Rui, Wu Di. Effect of pocket location on Combustion process in Natural Gas-Fueled Rotary Engine[J]. Applied Mechanics and Materials, 2013, 316-317: 73-79.

[16] XING Dong. Rotary polygonal piston engine[M]. Beijing: Science Press, 1981. [17] ZENG Zi-qiang, ZHANG Yu-fang. Natural gas gathering and transportation

project[M]. Beijing Petroleum Industry Press, 2001.11. [18] XIAO Man. Numerical study in work process of air-powered rotary engine[D].

Jiangsu university, 2016.

journal of computing and electronic information management ... · journal of computing and...

Documents