effect of compression ratio

Abstract—This paper highlights the evolution and features of

free-piston engine and presents the experimental and simulation analysis performed on UTP free-piston linear generator engine. The effect of applied voltage during starting the engine and the compression ratio on the operation of the engine is investigated. The result showed that the higher the applied voltage used for motoring the engine, the higher the peak pressure developed in the combustion cylinder. Further, the analysis indicated that for higher applied voltage, higher compression pressure starts to occur in the early period of combustion and showed lesser combustion duration. It is investigated that higher compression ratio leads to higher engine speed, which yields higher IMEP and rate of heat release. It is concluded that maximum engine power, rate of heat release, and cumulative IMEP are produced in free-piston engine by applying higher voltage during starting and using higher compression ratio.

Keywords—Free-piston engine, Internal combustion engine, Linear generator, Hybrid electric vehicle

I. INTRODUCTION

HE fluctuation of energy costs and supplies and the increasing awareness of pollution made it important to

develop strategies to mitigate the problems to seek alternative energy generation and utilization. Hence, more researches have been undertaken to improve the current internal combustion engine, which accounts for major pollution of the environment. The configuration of the current internal combustion engine is mainly represented by slide-crank mechanism, which restricts the motion of piston and attributed by many researchers as a drawback of the engine. However, this can be avoided by using free-piston engine, in which the engine’s pistons reciprocate linearly without the use of a crankshaft or flywheel. In essence, a free-piston engine is a machine that employs pistons which are dynamically coupled to energy storing and absorbing devices to convert thermal energy into a useful form [1]. The name “ free-piston” implies that there is no physical linkage that would constrain the piston’s motion leading to the potentially valuable feature of variable stroke length and compression ratio [2]. Some researchers also describe the free-piston engine as a linear engine because the piston, the only moving part of the engine, moves linearly back and forth [3]. The objective of the study is to investigate the effect of the applied voltage and compression ratio on the operation of free-piston linear generator engine.

All Authors are with Center for Automotive Research, Universiti

Teknologi Petronas, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia (Tel: +605 368 8000; Fax: +605 365 4090); E-mail: Abdulwehab A. Ibrahim ([email protected]); Ezrann Zharif Zainal Abidin ([email protected]); A. Rashid A. Aziz ([email protected]); Saiful A. Zulkifli ([email protected]);

A. Evolution of free-piston engine

The free-piston engine has gone through a long period of evolution and its concept can be traced back to James Watt’s steam engine that was patented in 1769. Before Watt’s steam engine was converted to rotary machine, it was a free-piston machine that uses gravity and power of steam to create piston’s reciprocating motion [4]. In the early age, several researchers were interested in the idea of free-piston engine in the years preceding World War II. In France, Raul Pateras Pescara started working on the free-piston engine air compressor around 1922 to use it as a compressed air supplier for helicopter propulsion units [5]. The first experimental Pescara’s air compressor was built around 1925 and was patented in 1928 [6, 7]. He was accredited for the invention of free-piston engine. Even though, his machine couldn’ t be developed into a practical helicopter application, later it paves the way for the development of commercial free-piston diesel compressor system and free-piston gas generator concept.

However, the development of free-piston engine gasifier abandoned in the mid-20th century due to advancement of gas turbine engine and disadvantage of free-piston engine [1, 8]. Once again, its development becomes a topic of interest in the application of hydraulic pump and linear generator. In hydraulic free-piston engine, the free-piston engine is directly coupled to a hydraulic pump compartment and an accumulator so that the chemical energy in the fuel is transformed in to hydraulic energy by means of linearly moving piston assembly. In free-piston engine linear generator, the free-piston engine is directly coupled to a linear electrical machine for electric power generation. In this paper, a free-piston linear electrical generator engine is considered in the study for the application of power generation.

B. Unique features of free-piston engine

The characteristics of free-piston engines differ from the traditional rotary engine mainly with the absence of crank mechanism in free-piston engine which is a good opportunity to eliminate a side load on the engine generated by crankshaft. According to Heywood, the presence of crankshaft, connecting rod and bearing accounts for the frictional losses occurring in the conventional engine [9]. Contrary to conventional engine, free-piston engine avoids these unnecessary moving parts and minimizes the frictional force. These features offer a great compactness, flexibility and high availability with low maintenance costs. Furthermore, the engine would be more quiet and vibrationless during the operation. The current engine requires torque transmission and multiplication, such as drive shaft, gearboxes and differentials, before their power

Abdulwehab A. Ibrahim, Ezrann Zharif Zainal Abidin, A. Rashid A. Aziz, and Saiful A. Zulkifli

on Free-Piston Linear Generator Engine

T

Effect of Compression Ratio and Applied Voltage

International Journal of Engineering and Physical Sciences 6 2012

394

utilized in vehicles. However, in Free-piston engine, the power generated can be transmitted either through wires to the motors or connected to the wheels with a hydraulic coupling to drive the vehicle. The unrestricted motion of the piston in free-piston engine resolved the challenges of obtaining variable compression ratio and stroke length that helps the engine to operate on almost any fuel without any major modification on the parts of the engine. This will help to minimize the air pollutions. However, this feature of the engine poses a main challenge to the engine. It requires developing a complex control system for monitoring the dynamic motion of the piston. Furthermore, it has been investigated that the engine has high cycle to cycle variation in the combustion process. Hence, it is clear that the feasibility of the free-piston engine will greatly depends on the design of sophisticated control system and it is beyond the scope of this paper to discuss with the control problems and solutions for free-piston.

C. Reported works on free-piston engine

For early free-piston engines, such as, free-piston engine air compressor and free-piston gas generator, a few papers presented the fundamental mathematical models and analyzed the engines [10-13], whereas most of the literatures primarily deal with the general descriptive of the engines and reported some experimental works [14-19]. For modern free-piston engine, such as, hydraulic free-piston engine and free-piston linear generator engine, contrary, a number of papers deal with the mathematical model and simulation of the engine [1, 20-26], with few of them reporting some experimental results from the developed prototype [27-29]

London and Oppenheim [12] developed the thermodynamic-dynamic model that represented the free-piston engine to study the design aspects of free-piston engine relative to the conventional crank-type reciprocating internal combustion engine system. They presented the full cycle study for the early free-piston engine types, namely, free-piston air compressor, free-piston gas generator and a combination of the two. Newton’s second law was applied for extraction of the resultant force versus piston position so that the integration of resulting equation yields the piston velocity and further integration results in piston position. Furthermore, affinity relations were employed to scale up or down the unit design. The study indicated that the free-piston system has better thermodynamic performance than the conventional engine. In a similar paper, they looked into the influence of compressor pressure ratio on the gas-generator output, gas-generator-turbine plant thermodynamic characteristics and piston geometrical and dynamical characteristics [30]. The result showed that higher compressor pressure ratio resulted in better compact and efficient system.

Bobrowsky [10] broadened the analytical analysis of free-piston gas generator by examining off-design operation of the free-piston engine, evaluating stability of the engine, introducing minimum geometry concept and defining fields of operations. He tried to look into the possibility of designing a unit to perform at some desired operating point and the

performance of the engine at off-design operating point. The combustion in the free-piston engine was assumed to proceed at constant volume and the exhaust pressure is assumed to be uniform and equal to the inlet pressure to the engine. It was noted that affinity relations was not used in the analysis for scaling up or down the engine, instead he employed dimensionless analysis since the result obtained may be scaled as required.

Performance analysis for hydraulic free-piston engine was developed and presented by Larmi et al. [23] using zero-dimensional and one-dimensional model, in which commercial GT-Power software was used for one-dimensional analysi. The simulated data was compared with the measured data from the prototype of the engine that was designed, constructed and tested in Tampere University of Technology at the Institute of Hydraulics and Automation. Both, the simulated and measured data showed around 80 bar in-cylinder pressure was developed inside the combustion chamber and 1200KJ/se rate of heat release was observed. Furthermore, it was observed that the power output of the engine was 11KW at the operating frequency of 28 Hz and compression ratio of 16:1. It was reported that the test engine could run only for very short periods [29].

It is worth to mention the numerical investigation and experimental work performed for a free-piston linear generator engine by WVU and Sandia National Laboratory researchers. WVU researchers developed a fundamental and numerical analysis of free-piston linear generator engine and presented in several published papers. Nandkumar [28] and Houdyschell [27] developed a fundamental and basic mathematical model for two-stroke spark ignited and diesel engine, respectively. Nandkumar solved the model and investigated the behaviour of the linear engine for different stroke-to-bore (L/b) ratios and under different air-to-fuel ratios. Similarly, Houdyschell studied the behavior of the engine for various bore, mass and heat input. He solved the model numerically to provide in-cylinder pressure profiles and several other operational characteristics of the engine as a function of time.

D. The linear generator project at UTP

Free-piston linear electrical generator engine was developed in Universiti Teknologi PETRONAS (UTP) in collaboration with Univesity of Malaya (UM) and Universiti Kebangsaan Malaysia (UKM) for being environmental friendly and using as a power generation unit to charge battery banks on-board for hybrid electric vehicle [31, 32]. After several developments of free-piston engine configurations, researchers at UTP come up with a two-stroke, linear engine type with dual piston assembly that is placed between two oppositely placed combustion chambers as shown in Fig. 1.


395

Translator shaft

Cylinder Head

Cylinder Block

Scavenging chamber

Engine Mounting

Permanent Magnets & Back

Iron Piston

Fig. 1 UTP two-stroke, free-piston linear generator engine prototype

The working principle of the engine is that a cycle starts

with the piston assembly at the bottom dead center at the left cylinder, assuming the piston moves from the right to the left. For starting the engine, the current is injected from the bank of three standard 12-volt automotive batteries connected in series to the alternator’s coil. The injected current allows the piston to move from the bottom dead center to the top dead center for the left cylinder. Hence, the pressure develops in the left combustion cylinder by transferring the energy from the moving piston to the charges during the compression process. Scavenging is controlled by the movement of the pistons. Fuel is injected and ignited when the piston arrives near the top dead center. The expansion process occurs in the left cylinder when the pistons moves back to the bottom dead center by converting thermal energy of the combustion products to kinetic energy of the piston. During the expansion process, some of the energy is absorbed by a linear electric motor to generate current. In the same time, the right cylinder undergoes compression process and when it reaches around top dead center, the fuel is injected in the right cylinder and combustion will occur and the piston will accelerate to the left and the cycle repeats.

II. RESEARCH METHODOLOGY

A. Mathematical model

The dynamic and thermodynamic model of the free-piston engine linear generator is developed to investigate the characteristics of the engine and the combustion process of free-piston linear generator engine; one can refer the detail of the development of the dynamic and thermodynamic analysis for free-piston engine in reference [33]. For dynamic analysis, Newton’s second law was applied, since the motion of the piston assembly of the engine is governed by the gas pressure developed in the left and right cylinders due to the combustion process ( )(tFc ) and by the balance of forces, such as cogging

( )(tFcog ), motoring ( )(tFmot ), and friction forces (f ), acting

on the piston assembly (Refer to (1)). Assuming the piston is moving from the left side to the right, the dynamic model of the free-piston linear generator engine is given us:

))()()((1

ftFtFtFm

F cogmotcx −−+=∑ (1)

For thermodynamic analysis, a single-zone model was developed by applying the first law of thermodynamics to the combustion chamber, supposing that mass cannot enter and leave the cylinder through the intake and exhaust system, hence, the cylinder content was a homogeneous charge of ideal gas (Refer to (2)). The model was implemented in Simulink/Matlab environment and analyzed.

dt

dQ

Vdt

dV

V

p

dt

dp n)1( −+−= γγ (2)

B. Experimental setup

The experiment was performed on a two-stroke, direct injection, UTP free-piston linear generator engine that consists of dual piston that was placed between two opposite combustion chamber, which has a specification of 76mm bore, 36.7mm nominal stoke length and 313cc/cycle engine capacity. The linear generator was mounted at the center of the piston assembly and consists of stator coil, three phase tubular permanent magnet and translator shaft that are connected to the two pistons of each cylinder, as shown in the Fig. 1.

The linear generator acts like a generator when the linear motion of the translator assembly reciprocates between two combustion chambers to produce electricity and can also acts like a motor when the current is injected to the alternator’s coil from the battery supply for starting the engine. The engine can be fuelled with compressed natural gas (CNG) and hydrogen. The main specifications of the test engine and a photo of the engine setup are shown in Table 1 and Fig. 2 respectively.

Using data acquisition system, cylinder pressure, the amount of current flowing into the coil and the corresponding piston linear displacement data for both cylinders was gathered. An electrical power was supplied from the standard 12-Volt automotive battery bank to the engine through the alternator’s coils for motoring the engine. In the experimental work, maximum five standard 12-volt automotive batteries could only be used due to the limitation of the MOSFET driver used in the experiment and the motoring was done without combustion [34].

Fig. 2 Experimental setup of UTP free-piston linear generator engine

and data acquisition system


396

TABLE I SPECIFICATION OF THE TEST ENGINE

Parameters Specification

Cylinder bore 76mm Nominal stroke 34.5mm

Engine Capacity 313cc/cycle Moving mass 6kg Nominal Compression Ratio 14:1

The data was logged at 0.125mm linear displacement

resolution and a maximum of 75 consecutive engine cycles could be recorded for different engine operating scenario using developed LABVIEW program. The collected experimental data was post-processed by using MATLAB software. The detail result of the experiment is presented in the subsequent sub-sections.

III. RESULTS AND DISCUSSIONS

A. Effect of voltage applied

The effect of voltage applied for motoring the engine was studied to determine the voltage required to start the engine and to achieve stable operation. Both simulation and experimental work were performed by varying the applied voltage during start-up. Three and five automotives batteries connected in series for the experiment producing voltages of 36 and 60 volts respectively. Fig. 3 and 4 show the piston motion with no combustion. It was observed that the cycle-to-cycle variation was not prevalent for motoring the engine without combustion for both cases. However, higher engine frequency (345cpm vs 240cpm) and in-cylinder pressure (4.95bar vs 4.023bar) were observed in the case of 60 volts.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-40

-30

-20

-10

0

10

20

30

40

Time [se]

Dis

pla

cem

en

t [m

m]

Using 36VUsing 60V

Fig. 3 Experimental result of displacement versus time for free-piston

linear engine for various applied voltage

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

Time [se]

Pre

ssu

re [

ba

r]

Using 36VUsing 60V

Fig. 4 Experimental result of pressure versus time for various applied

voltage In the simulation, the current was applied for motoring the

engine until the piston reached ignition position and then combustion was initiated. The simulation was performed by applying 36, 60, 96 and 144 voltes for motoring of the engine. The result indicates that the piston stopped short of full amplitude using a 36V as compared to using 60 and 144V. The full stroke length could be obtained when 96V and above were applied in the simulation. The frequency and acceleration of the piston were lower in the case of 36V due to the lower speed of the piston. The variation of piston displacement and acceleration with time for 36, 60 and 144V are depicted in Fig. 5 and 6 respectively.

0 0.025 0.05 0.075 0.1 0.125 0.15-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

Time [se]

Dis

pla

cem

en

t [m

]

Using 36VUsing 60VUsing 144V

Fig. 5 Simulation result of piston displacement versus time for

various applied voltage


397

0.03 0.04 0.05 0.06 0.07 0.08 0.09-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

Time [se]

Acc

ele

ratio

n [m

2 /s]


Fig. 6 Simulation result of piston acceleration versus time for various

applied voltage

Fig. 7 shows the simulation result of pressure versus time applying various voltages. The analysis revealed that higher in-cylinder pressure was developed for 96V and 144V than the other applied voltages. i.e the higher the used current, the higher the pressure developed in the combustion cylinder. The maximum peak pressure obtained for 36, 60, 96 and 144V were 22.067, 25.831, 32.20 and 32.996 bar, respectively. Hence, it was observed that applying 96 and 144V developed sufficient pressure to initiate combustion and overcome misfiring. The variation of in-cylinder pressure with volume for different applied voltage is portrayed in Fig. 8.

0 0.005 0.01 0.015 0.02 0.025 0.03 0.0350

5

10

15

20

25

30

35

Time [se]

Pre

ssu

re [

ba

r]

Using 36VUsing 60VUsing 96VUsing 144V

Fig. 7 Simulation result of pressure versus time of free-piston linear

engine for various applied voltage

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5

x 10-4

0

5

10

15

20

25

30

35

Volume [m3]

Pre

ssu

re [

ba

r]


Fig. 8 Simulated in-cylinder pressure versus volume for various

applied voltage The rate of heat release and cumulative indicated mean

effective pressure (IMEP) were determined for different applied voltage in simulation and plotted in Fig. 9 and 10 respectively. As it can be seen that the cumulative IMEP for the 36, 60, 96 and 144V were 0.822, 0.975, 1.308 and 1.347 bar and the maximum rate of heat release were 40, 48, 70 and 75KJ/se, respectively. Confirming that higher indicated power can be extracted from higher engine frequencies as expected. Further analysis indicated that as the applied voltage were increased, higher rate of compression pressure and shorter combustion duration were achieved as shown in Fig. 7 and 9. The pressure and rate of heat release profiles depicted in Fig. 7 and 9 show that most of the combustion heat was released after the peak pressure around Top Dead Center (TDC).

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-20

-10

0

10

20

30

40

50

60

70

80

Time [se]

Ra

te o

f h

ea

t re

lea

se [

KJ/

se]


Fig. 9 Simulation result of rate of heat release versus time for various

applied voltage


398

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

Time [se]

Cu

mu

lativ

e IM

EP

[ba

r]


Fig. 10 Simulation result of cumulative IMEP versus time for various

applied voltage

B. Effect of compression ratio

Fig. 11 shows the simulation results of displacement versus time for different compression ratios of the free-piston linear generator engine. As discussed in the above section, the main advantage of free-piston engine is that it allows changing the compression ratio of the engine without putting much effort in the system. In the simulation, it is shown that increasing the compression ratio of the engine resulted in a higher operating frequency of the engine due to the higher pressure developed in the cylinder as shown in Fig. 11 and 12. Similarly, higher compression ratios lead to higher engine speeds and hence the piston assembly moves faster (see Fig. 13).

0.02 0.04 0.06 0.08 0.1 0.12 0.14-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

Time [se]

Dis

pla

cem

en

t [m

]

Full strokeCR=29.58CR=25.21CR=17.25CR=12.59

Fig. 11 Simulation result of displacement versus time for different

compression ratios

0.1 0.35 0.6 0.85 1.1 1.35 1.6 1.85 2.1 2.35 2.6

x 10-4

0

0.5

1

1.5

2

2.5

3x 10

6

Volume [m3]

Pre

ssu

re [

Pa

]

CR=29.58CR=25.21CR=17.25CR=12.59

Fig. 12 Simulation result of pressure versus volume of for different

compression ratios

-0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04

-6

-4

-2

0

2

4

6

Displacement [m]

Ve

loci

ty [

m/s2 ]

Full strokeCR=29.58CR=25.21CR=17.25CR=12.59

Fig. 13 Simulation result of velocity versus displacement for different

compression ratios Further analysis pointed out that increasing the compression

ratio yielded higher IMEP and rate of heat release as indicated in Fig. 14 and 15. Therefore, higher power density of the engine can be achieved by increasing the compression ratio and resulting in higher frequency of the piston motion. As shown in Fig. 15, lower compression ratio led to longer time delay and total heat release period. In a free-piston engine, it is necessary that the maximum hear release should occur after TDC to increase the expansion work. If the maximum heat release occurs before TDC, the piston accelerates rapidly away from TDC reducing the time available for combustion and resulting in lower expansion force as there is no flywheel or crankshaft.


399

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-3

-2

-1

0

1

2

3

Time [se]

Cu

mu

lativ

e I

ME

P [

ba

r]

CR=29.58CR=25.21CR=17.25CR=12.59Full stroke

Fig. 14 Simulation result of cumulative IMEP versus time for

different compression ratios

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035-10

0

10

20

30

40

50

60

70

Time [se]

Ra

te o

f h

ea

t re

lea

se [

KJ/

se]

CR=29.58

CR=25.21

CR=17.25

CR=12.59

Fig. 15 Simulation result of rate of heat release versus time for

different compression ratios

IV. CONCLUSION

The experimental and simulation result show that higher in-cylinder pressure is developed in the cylinder by injecting higher current into the alternator’s coil. Furthermore, it is revealed that the maximum engine power, rate of heat release, and cumulative IMEP are produced by applying higher voltage during starting and higher compression ratio. It is concluded that further study is required to understand the operation of the engine to benefit from free-piston engine’s advantage and revolutionize the existing internal combustion engine.

ACKNOWLEDGMENT

We would like to thank the Universiti Teknologi PETRONAS for providing grant and facilities for the research.

REFERENCES

[1] H. T. Aichlmayr, "Design considerations, modeling and analysis of micro-homogenous charge compression ignition combustion free-piston engine," PhD thesis, University of Minnesota, Minnesota, 2002.

[2] P. Němeček, M. Šindelka and O. Vysoký, "Ensuring steady operation of free-piston generator," Journal of Systemics, Cybernetics and Informatics, vol. 4, pp. 19-23, 2006.

[3] C. Tóth-Nagy, "Linear engine development for series hybrid electric vehicles," PhD, Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia, 2004.

[4] C. Tóth-Nagy and N. N. Clark, "The linear engine in 2004," SAE paper vol. 2005-01-2140, 2005.

[5] A. L. London, "Free-piston and turbine compound engine-status of the development," SAE Transactions, vol. 62, pp. 426-436, 1954.

[6] J. B. Heywood and E. Sher, The two-stroke cycle engine: Its development, operation, and design. London: Taylor & Francis, 1999.

[7] T. T. Company, "Free piston engine," Lubrication, vol. XLIV, pp. 113-132, September 1958.

[8] R. Mikalsen and A. P. Roskilly, "A review of free-piston engine history and applications," Applied Thermal Engineering, vol. 27, pp. 2339-2352, 2007.

[9] J. B. Heywood, International combustion engine fundamentals: McGraw-Hill, 1988.

[10] A. R. Bobrowsky, "Analytical methods for performance estimates of free-piston gasifiers," presented at the ASME Gas Turbine Power Conference, Detroit, 1957.

[11] A. L. London, "The free-piston-and turbine compound engine- A cycle analysis," Trans. ASME, vol. 77, pp. 197-210, 1955.

[12] A. L. London and A. K. Oppenheim, "The free-piston engine development-present status and design aspects," Trans. ASME, vol. 74, pp. 1349-1361, 1952.

[13] S. L. Soo and W. A. Morain, "Some design aspects of the free-piston gas-generator turbine plant-Part. I: Thermodynamics and component characteristics," ASME Paper 55-A-146, pp. 1-45, 1955.

[14] R. A. Lasley and F. M. Lewis, "The development of high-output free-piston gas generators," Trans. ASME, vol. 76, pp. 453-462, 1954.

[15] J. J. McMullen and W. G. Payne, "Performance of free-piston gas generators," Trans. ASME, vol. 76, pp. 1-13, 1954.

[16] J. J. McMullen and R. P. Ramsey, "The free-piston type of gas-turbine plant and applications," Trans. ASME, vol. 70, pp. 15-29, 1954.

[17] F. A. I. Muntz and M. Barthalon, "Free-piston progress," A.S.N.E Journal, vol. 70, pp. 749-755, 1958.

[18] F. A. I. Muntz and R. Huber, "The free-piston gas-generator turbine as a power plant for ship propulsion," Institute of Marine Engineers Transactions, vol. 66, pp. 946-952, 1954.

[19] O. B. Noren and R. L. Erwin, "The future of the free-piston engine in commercial vehicles," SAE Transactions, vol. 66, pp. 305-314, 1958.

[20] C. M. Atkinson, et al., "Numerical simulation of a two-stroke liner engine-alternator combination," SAE Paper, vol. 1999-01-0921, 1999.

[21] N. N. Clark, S. Nandkumar, and P. Famouri, "Fundamental analysis of a linear two-cylinder internal combustion engine," SAE Paper, vol. 982692, 1998.

[22] S. S. Goldsborough and P. Van Blarigan, "Optimizing the scavenging system for a two-stroke cycle, free piston engine for high efficiency and low emissions: A computational approach," SAE Paper, vol. 2003-01-0001, 2003.

[23] M. Larmi, S. Isaksson, S. Tikkanen, and M. Lammila,"Performance simulation of a compression ignition free piston engine," SAE Paper, vol. 2001-01-0280, 2001.

[24] R. Mikalsen and A. P. Roskilly, "The design and simulation of a two-stroke free-piston compression ignition engine for electrical power generation," Applied Thermal Engineering, vol. 28, pp. 589-600, 2008.

[25] E. Shoukry, S. Taylor, N. Clark, and P. Famouri,"Numerical simulation for parametric study of a two-stroke direct injection linear engine," SAE Paper, 2002.

[26] P. Van Blarigan, N. Paradiso, and S. Goldsborough,"Homogeneous charge compression ignition with a free piston: A new approach to ideal Otto cycle performance," SAE Paper, vol. 982484, 1998.

[27] D. Houdyschell, "A diesel two-stroke linear engine," M.Sc. thesis, Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia, 2000.

[28] S. Nandkumar, "Two-stroke linear engine," M.Sc. thesis M.Sc. Thesis, Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia, 1998.


400

[29] S. Tikkanen, M. Lammila, M. Herranen, and M. Vilenius, "First cycles of the dual hydraulic free piston engine," SAE Paper, vol. 2000-01-2546, 2000.

[30] A. K. Oppenheim and A. L. London, "Design analysis of free-piston engines," Automotive Industries, pp. 46-50, 76, 1950.

[31] A. R. A.Aziz, "Design and development of a prototype free piston linear generator engine," presented at the National R & D Symposium, Tronoh, 2003.

[32] S. A. Zulkifli, "Modeling, simulation and implementation of rectangular commutation for starting of free-piston linear generator," MSc thesis, Department of Electrical and Electronic Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 2007.

[33] A. A. Ibrahim and A. R. A. Aziz, "Dynamic and thermodynamic analysis of two-stroke, dual cylinder, linear combustion engine," presented at the International Conference on Advances in Mechanical Engineering (ICAME), Shah Alam, Malaysia, 2009.

[34] A. A. Ibrahim, A. R. A. Aziz, E. Z. Z. Abidin, and S. A. Zulkifli, "The operation of free piston linear generator engine using MOSFET and IGBT drivers " Journal of Applied Sciences (in-press), 2011.


401

effect of compression ratio

Documents