Open Access Design and Optimization of Feedforward-PID Integrated Controller for Pre-Injection Numerical Control Air-Powered Engine

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1 Send Orders for Rerints to 56 The Oen Automation and Control Systems Journal, 5, 7, 56-6 Oen Access Design and Otimization of Feedforard-PID Integrated Controller for Pre-Injection Numerical Control Air-Poered Engine Zhao Caihong,*, Chen Shian and Zhang Shijin Nanhang Jincheng College, Nanjing 56, P.R. China School of Automotive and Traffic Engineering, Jiangsu University, Zhenjiang, P.R. China Abstract: A feedforard-pid integrated controller is develoed and otimized for the re-injection numerical control (NC) air-oered engine (PINCAPE) to track the exected seed quickly and accurately. The roosed integrated controller comrises to arts, namely a feedforard controller and a PID one. According to the real-time orkload and the exected seed, the feedforard controller uses a numerical fitting function to determine the main art of the suly air ressure to obtain good stable accuracy. The function is develoed ith the outut of the suly air ressure, and the inuts of the engine seed and the outut oer, hich are based on the different steady-state oerations of the engine. To imrove the engine resonse erformance, the PID controller gives the fine-tuning of the suly air ressure ith the inut of the difference beteen the exected seed and the real-time seed. The arameters of the PID controller are otimized according to the genetic algorithm, ith an objective function that minimizes the mean square of the seed error. The results sho that the otimized feedforard-pid integrated controller shortens the resonse time of the PINCAPE by more than 47% and 64.5% under varied set oint seed and engine load variations resectively, comared ith the single feedforard controller. Furthermore, the resonse steady state error of the feedforard-pid integrated controller is less than %, hich erfectly satisfies the control secification. Keyords: Air-oered engine, feedforard-pid integrated controller, genetic algorithm, NC, re-injection.. INTRODUCTION To major roblems that are facing our orld today are the environment ollution and the energy crisis. The environment ollution and the energy crisis are due to more vehicles, most of hich are oered by internal combustion engines using fossil fuel [, ]. The air-oered engine can give reneable oer and zero emission because that is driven by comressed air hich can be roduced from solar, ind energy, ater energy and so on [-7]. Therefore the air-oered engine becomes more oular and is regarded as one of the ideal oer sources for future vehicles. Although there is an air-oered sash late engine reorted [8], most of air-oered engines resemble to common internal combustion engines. The air-oered engine at least has a cylinder, a iston, a crank, a valve train system, and so on. During the air-oered engine oeration, there are orking stroke and exhaust stroke. With the hel of the valve train system, the orking stroke uts comressed air into the cylinder and exands. The high ressure air exansion gives oer by the iston and the crank motion. Exhaust stroke gets rid of exanded ressure air from the cylinder. *Address corresondence to this author at the School of Mechanical Engineering, Nanhang Jincheng College, Nanjing, Jiangsu, 56, P.R. China; Tel: ; @qq.com Air intake and exhaust of the air-oered engine are through by intake and exhaust valves of the valve train system. Because intake air ressure is much larger than the atmosheric ressure, there are difficulties in seals of the valve train system. To settle don these difficulties, a re-injection numerical control air-oered engine (PINCAPE) is firstly given by the authors [9]. Fig. () shos the orking scheme of the PINCAPE. The PINCAPE is at least made of a third high-ressure air tank, a re-injection cylinder, solenoid valves, sensors and an ontology engine, ithout a valve timing mechanism. The reinjection cylinder and the controlled solenoid valves are set to erform the functions of the valve train system, so these seal matters in the valve train system are exected to be settled don and the energy (mass of comressed air) to the PINCAPE can be recisely rovided according to its oer requirement. Chen et al. resented resective influences of intake advance angle, basal of intake sustain angle, exhaust advance angle and exhaust delay angle on the energy conversion efficiency and the outut torque of the air-oered engine []. Hoever, their model as not dynamic since it is based on the angular coordinate ithout time variation. The aer develoed a non-linear model of the PINCAPE that fully dislayed inner thermodynamic characteristics /5 5 Bentham Oen

2 Design and Otimization of Feedforard-PID Integrated Controller The Oen Automation and Control Systems Journal, 5, Volume 7 57 Solenoid valve Third high-ressure air tank W, T, T,V, T,V Solenoid valve Pre-injection cylinder Solenoid valve Solenoid valve Q T a Working cylinder ω Fig. (). orking scheme of PINCAPE. The engine ith good erformances should resond quickly and recisely to the seed oeration. The seed control method of the existing air-oered engine ith a valve train system is similar to the common internal combustion engine. The current method uses a governor to change the effective flo area of air intake to the cylinder to control the outut oer (or torque). Although the mechanical governor relaced by an electronic governor, the control accuracy and energy efficiency is not ideal []. The reason is that the control rocedure is synchronous ith the air intake rocess. The PINCAPE has a characteristic that the amount of comressed air intake is reared in advance of comressed air intake of the orking cylinder. Hence, higher control accuracy and higher energy efficiency is exected to reach hen a good seed control controller is adoted for the PINCAPE. To imrove resonse rate and control accuracy to the exected seed of the seed oeration, the aer rooses and otimizes a feedforard-pid integrated controller for PIN- CAPE. The feedforard-pid integrated controller consists of a feedforard controller and a PID controller. The feedforard controller lays the role to decide the main suly ressure of the re-injection cylinder to obtain good stable accuracy. The PID controller lays the role to decide the fine tuning suly ressure to fasten the engine s resonse rate. To achieve a good control effect, the PID control arameters are otimized according to the genetic algorithm (GA) [, ].. THERMO-DYNAMICS MODEL OF PINCAPE As shon in Fig. (), during the orking stroke, the solenoid valve oens, after comressed air flos into the orking cylinder from the re-injection cylinder to drive the iston and the crank, the ontology engine sulies oer by the flyheel. There are those basic hyotheses []: () The high-ressure air is ideal gas. () and T are constants hich are the absolute ressure and the absolute temerature in the third high-ressure air tank resectively. () Equal ressure and equal temerature are throughout the re-injection cylinder and the orking cylinder. Control strategies of the solenoid valves, and are arranged as follos. () The solenoid valve oens at the start of the exhaust stroke and closes hen the exected control ressure of the re-injection cylinder ec is reached. () The solenoid valve just oens during the orking stroke. () The solenoid valve oens during the exhaust stroke and hen the absolute ressure in the orking cylinder is larger than the atmosheric ressure a. K, K and K, the sitching values of the solenoid valves, and, are exressed as. K = hardlim( ec ) ( K) K = hardlim[sin( ωt)] K = hardlim( a) ( K) Where the hardlim ( ) is the hard-limit transfer function, ω is the engine seed ith the unit of rad/s, t is time... Thermo-Flo Rate Model of Pre-Injection Cylinder During intake and exhaust of the re-injection cylinder, there are thermodynamics equations as follos [4]. du dh dh = K K () du d( mu) d( mcvt) = = () V () = mrt (4) dh dm dm = h = ct = ctq (5) dh = h dm = c T dm = c T q (6) Where U, H and H are the internal energy in the reinjection cylinder, the enthaly floing through the solenoid valve and the enthaly floing through the solenoid valve resectively; c and c V are the secific heat caacity at constant ressure and the secific heat caacity at constant volume resectively; m is the air mass ithin the re-injection cylinder; m and m are the air mass floing through the solenoid valve and the air mass floing through the solenoid valve resectively; h and u are the secific enthaly and the secific internal energy of the air in the re-injection cylinder resectively; h is the secific enthaly of the air in the third high-ressure air tank; R is the gas constant; q and q are the air flo through the solenoid valve and the air flo through the solenoid valve resectively.

3 58 The Oen Automation and Control Systems Journal, 5, Volume 7 Caihong et al. The ressure-flo equations of during intake and exhaust of the re-injection cylinder are ritten as follos. q q k = A φ( σ), σ = k RT k = A φ ( σ ), σ = k RT Where A and A are the effective floing area of the solenoid valve and the effective floing area of the solenoid valve resectively; k is the secific heat ratio; φ and φ are the stream functions associated ith the ressure different through the solenoid valves and resectively. φ and φ are ritten as follos []. k + k k σi σi, σi >.58 φi( σi) = ( i =,) (8) k + k k ( ) ( ), σ i.58 k+ k+ d (7) Take Equations (), (4), (5) and (6) into Equation (), can be exressed as folloing. d krt = ( ) ( ) (9) V V krt K q K q.. Thermo-Flo Rate Model of Working Cylinder During the orking stroke and the exhaust stroke of the orking cylinder, there are thermodynamics equations as follos. dq du dh dh dw = K + K + () du d( mu) d( mcvt) = = () V = mrt () dq dh dw = aa( T T) () g g a = h dm = c T dm = c T q (4) dv = (5) Where Q, U, H and W are the heat exchange beteen the air ithin the orking cylinder and the environment, the internal energy ithin the orking cylinder, the enthaly floing through the solenoid valve and the oer from comressed air ithin the orking cylinder to the iston resectively; m is the air mass ithin the orking cylinder; m is the air mass floing through the solenoid valve ; h and u are the secific enthaly and the secific internal energy of the air ithin the orking cylinder resectively; q is the air flo through the solenoid valve; a g is the heat exchange coefficient beteen the air ithin the orking cylinder and the environment [5]; A g is the heat exchange area; T a and T are the atmosheric temerature and the air temerature ithin the orking cylinder resectively; V is the orking volume of the orking cylinder. ag =.8 ω T.4 5 = ω T (6) k a q = A φ ( σ ), σ = k RT k + k k σ σ σ >.58 φ( σ) = k + k k ( ) ( ) σ.58 k+ k+ dv V, A g, and a g are ritten as follos [6, 7]. V Vh (7) (8) Vh λ = V + ( cos ϕ+ sin ϕ) (9) = rs () π D S = () λsin ϕ Ag = S+ π Dr( cos ϕ + ) () dv ωvh λ = (sinϕ+ sin ϕ) ()! =!" (4) Where A is the effective floing area of the solenoid valve ; V is the minimum of V ; V h is the dislacement of the orking cylinder; ϕ is the engine dislacement; r is the radius of the crank; λ is the connecting rod ratio; D is the diameter of the orking cylinder; S is the cross-sectional area of the orking cylinder resectively. Takeing Equations (), (), (), (4), (5) and (9) into Equation (), d can be exressed as folloing. d RagAg krt = ( Ta T) + ( K q) c V V V krt k dv ( K q ) V V t d.. Dynamics Model of Ontology Engine (5) When kinematics analyses and dynamics analyses on the ontology engine are carried out, folloing equations are obtained.

4 Design and Otimization of Feedforard-PID Integrated Controller The Oen Automation and Control Systems Journal, 5, Volume 7 59 M r S mrω ϕ λ ϕ = [( a) i (cos + cos )] λsin ϕ (sin ϕ + ) λ sin ϕ (6) M! M l = I f!!! (7) Where M and M l are the torque outut of the iston and the resisting torque of the engine load resectively; I f is the moment of inertia on the flyheel; m i is the recirocating mass in the orking cylinder. M l is given as follos [8]. Ml = Mlsign( ω) + klω, ω Ml Ml Ml, ω = (8) Where k l is the linear resisting torque coefficient; M l is the coulomb daming of the engine.. DESIGN OF FEEDFORWARD-PID INTEGRATED CONTROLLER FOR PINCAPE The design and otimization of the feedforard-pid integrated controller for the PINCAPE are emloyed by numerical simulations. The PINCAPE is reformed from an S95 engine, the arameter values in simulations are listed in Table. Table. Parameters in simulation. Parameter Value Parameter Value A / m k.4 A / m c V / J kg - K A / m c / J kg - K - 5 D / m.95 R/ J kg - K r / m.575 / Pa 7 λ.78 a / Pa. 5 V / m / Pa 6 V / m -5 / Pa. 5 m i / kg.5 T a / K M l / N m. T / K I f / kg m.5 T / K ω /rad s -.94,, T, T and ω are the initial values of,, T, T and ω resectively. When M l is set as constant (k l =.5 N m s rad - ), ec is changed among.8 MPa,.6 MPa and.4 MPa, the n r - t curves of the PINCAPE are given in Fig. (). Here, n r is the real-time seed of the engine. n r / (rm) Fig. (). n r - t curve of PINCAPE. Fig. () shos that the start-u of the PINCAPE is good because it is into orking stably less than.5 seconds after start. The engine seed increases in air stroke and decreases in exhaust stroke hen the engine is stably orking and similar to common internal combustion engines. Hence, the model of PINCAPE develoed in this aer is dynamic and feasible. The vehicle equied ith a PINCAPE needs to track the exected seed quickly and accurately. A slo seed resonse of the engine ill cause a bad vehicle dynamic erformance and bring large engine seed fluctuations hich lead to bad comforts. To satisfy this objective, an integrated controller ith feedforard- PID aroach is introduced. In a PINCAPE seed control system, the engine seed is controlled by ec, the exected control ressure of the reinjection cylinder [9]. The control inut is calculated from the real-time engine load k l, the exected seed n tgt and the real-time engine seed n r. k l and n r can be measured by the crank sensors. Fig. () shos the block diagram of the feedforard-pid integrated controller. Seed Oeration Feedforard Controller ec + + Δ ec PID Controller ec Liner Real-Time Load PINCAPE Real-Time Load Filtering ec =.4 Ma ec =.6 Ma ec =.8 Ma Torque Outut Seed Outut System Oututs Fig. (). block diagram of feedforard-pid integrated controller. The feedforard-pid integrated controller gives ec hich is the hole control ressure. ec is set to equal the sum of the main suly ressure of the re-injection cylinder ec and the fine tuning suly ressure of the re-injection cylinder Δ. ec ec and Δ are given by a feedforard ec loo and a PID loo resectively.

5 6 The Oen Automation and Control Systems Journal, 5, Volume 7 Caihong et al... Feedforard Controller The feedforard controller gives ec by using =( ) ec f n tgt,, here the control function of tgt ec is exressed by n tgt and tgt. tgt is the outut oer of the engine under k l and n tgt. tgt is ritten as follos. πntgt tgt = k l k l = M r! M lr! I f!! +. (9) () Where M r is the measured value by the torque sensor on the crank, and M lr is the value of idling oeration. To obtain stable tgt, k l is relaced by k lr, hich is filtered value of k l by using an Analog Filter design in Simulink [9, ]. =( ) ec f n tgt, is extremely imortant to the feedforard controller. In order to obtain an accurate ec, the func- tgt tion is established through numerical fitting method according to data of sec, n s and s, hich are obtained in many different steady state engine oerations. The data needed in numerical fitting are shon in Accessory. sec is exressed as folloing. = a n + a + a n + a n sec s s s s s + a + a n + + a j j j s L j s L j( j+) s ( ) () Where a ~a j(j+) are fitting arameters resectively. δ, hich is the residual beteen secf and sec, is introduced by []. h ( secfi seci )/ h i= δ = h ( seci )/ h i= () Where h is the measuring oint number, secf is the fitted value of sec. When j equals to, and 4 resectively, the corresonding values of δ are listed in Table. Table. Residuals fitted of feedforard control function.. PID Controller A standard PID controller, hich is made of the roortional, the integral and derivative [], is ritten as follos. t de Δ ec = ke+ ki e+ k d (4) e= ntgt n (5) Where Δ is the fine tuning suly ressure to comensate the feedforard action to track the exected seed; ec k, k i and k d are the roortional, integral and derivative arameters resectively. In vie that n r is fluctuating even if the engine orks stably. To ensure the PID controller orks smoothly, n r is relaced by n, hich is the real-time mean value of n r. 4. OPTIMIZED RESULTS AND COMPARISON A seed oeration has been alied for otimizing arameters of the designed feedforard-pid integrated controller hich is that the initial engine seed as rm, in ~5 s the exected seed is 9 rm, in 5- s the exected seed is rm, in -45 s the exected seed is 9 rm, and k l is.5 N m s rad -. We roose a determination method to minimize the function belo. t J e = (6) mutation crossover initiation seed oeration PINCAPE control arameters caculating fitness function j 4 select NO recision is satisfied? δ Table shos that δ is minimal hen j equals to. Therefore, the maniulated variables of the feedforard control loo based on steady state function Equation () can be calculated by (, ) = f n = n + n ec tgt tgt tgt tgt tgt 5.44n n tgt tgt tgt tgt +.45n +.457n -.64 tgt tgt tgt tgt tgt () end YES Fig. (4). Flo chart for otimizing the feedforard-pid integrated controller based on GA. The genetic algorithm (GA) is a oerful search technique hich has been alied to many ractical roblems. Hence, GA is chosen as the otimizing method for the feedforard-pid integrated controller []. During otimization rocedure, GA iteratively maniulates oulations of these

6 Design and Otimization of Feedforard-PID Integrated Controller The Oen Automation and Control Systems Journal, 5, Volume 7 6 chromosomes using reroduction, crossover and mutation oerations, and evaluates suitability of each solution using a fitness function. Here the otimization objective function J is taken as the fitness function. Chromosomes ith a good fit are carried forard into the next generation and are subsequently used as the basis for generating ne and imroved solutions. The search rocedure continues iteratively until the secified termination conditions have been satisfied. It is that the solution ith desired fitness is satisfied for a secified number of generations. Flo chart for otimizing the feedforard-pid integrated controller based on GA is shon in Fig. (4). The arameters for the GA-based otimizing rocedure are selected as follos. ) Maximum number of generation: 5; ) Initial oulation size: 6; ) Crossover robability:.9; 4) Mutation robability:.7; 5) Generation ga:.9; 6) k d [, 5], k i [, 5] and k [, 5]. Consequently, after 5 generations, k d =.7, k i =65. and k =99.5 are obtained, change of oulation otimal solution is shon in Fig. (5). The n-t curves and ec -t curves are shon in Figs. (6, 7) n/ (rm) Fig. (6). n-t curves hen n tgt varies. Execting seed Feedforard-PID integrated controller Feedforard controller To verify the efficacy of the feedforard-pid integrated controller, intermittent oerations at load variations are simulated. The intermittent oerations are that n tgt is fixed to 9 rm, the k l as varied from. N m s rad - to N m s rad - at the5th second and from N m s rad - to. N m s rad - at the th second. The k lr -t curve, n-t curves and ec -t curves are shon in Figs. (8-). Fig. (9). shos hen k l varies, the feedforard controller takes.s and 5.8s to stably reach 9 rm. The corresonding times of the feedforard-pid integrated controller are.4s and.45s resectively. The reason is that the feedforard-pid integrated controller gives much bigger ec hen k l increases and vice verse as shon in Fig. (). Therefore, the feedforard-pid integrated controller has a good robustness. J Number of generation Fig. (5). Change of oulation otimal solution. ec / (MPa) 5 4 Feedforard-PID integrated controller Feedforard controller Fig. (6) shos the feedforard controller takes.4s from rm to 9 rm,.6s from 9 rm to rm, and.s from rm to 9 rm. The corresonding times of the feedforard-pid integrated controller are.8s,.49s, and.69s, resectively. Thus, the feedforard-pid integrated controller is faster than the feedforard controller. As shon in Fig. (7), the reason is that the PID controller lays useful roles to imrove the control comensation erformance. Fig. (6) shos that e is rm hen the engine stably orks at 9rm and e is 8 rm hen the engine stably orks at rm. Therefore, the feedforard-pid integrated controller has an ability of tracking the seed oeration accurately Fig. (7). ec -t curves hen n tgt varies. CONCLUSION Based on the thermo-dynamics model of PINCAPE, this aer designs a robust feedforard-pid integrated controller that includes a feedforard controller and a PID controller to imlement the engine seed control. For the tracking, accuracy and robustness, e comare ith the feedforard con-

7 6 The Oen Automation and Control Systems Journal, 5, Volume 7 Caihong et al. troller used only and confirm the effectiveness of the roosed controller. Table. n s and s recorded in each sec. sec (MPa) n s (r/min) s (kw) sec (MPa) n s (r/min) s (kw) k lr / (Nm s rad - ) Fig. (8). k lr -t curve. n/ (rm) Fig. (9). n-t curves hen k l varies. ec / (MPa) Fig. (). ec -t curves hen k l varies. In the future e lan to erform exeriments about a feedforard-pid integrated controller, not only verity this control method, but also offer a reference for using of control on PINCAPE. ACCESSORY All of data are recorded in Table Execting seed Feedforard-PID integrated controller Feedforard controller Feedforard-PID integrated controller Feedforard controller CONFLICT OF INTEREST The authors confirm that this article content has no conflict of interest.

8 Design and Otimization of Feedforard-PID Integrated Controller The Oen Automation and Control Systems Journal, 5, Volume 7 6 ACKNOWLEDGEMENTS This research is financially suorted by the National Natural Science Fund Project of China under the contract and the Scientific Research Foundation for Talented Scholars of Jiangsu University under the contract 6jdg4. REFERENCES [] L.G. Liu, Develoment and research of the automobile in the st century, Chinese Journal of Automobile Research and Develoment, no.,. 8-,. [] Y. Z. Bian, Automobile Ne Energy Technology, Beijing: Peole s Traffic Press,. [] J. Williams, C. Knolen, A. T, Mattick and A. Hertzberg, Quasi Isothermal Exansion Engines For Liquid Nitrogen Automotive Proulsion, SAE Paer, no , 997. [4] H. Liu, Y. Chen and G.L. Tao, Researches on characteristics and model of ork rocess of comressed air oered engine, Progress in Natural Science, no. 4,. 9-4, 4. [5] P.L. Chen, X.L. Yu and L. Liu, Simulation and exerimental study of electro-neumatic valve used in air-oered engine, Journal of Zhejiang University (Science A), no.,. 77-8, 9. [6] H.G. Liu, B.B. Gu, F. Qiu and S.A. Chen, Testing and Numerical Fitting of Cornering Stiffness of 7.5R 4PR PWTire, Tractor & Farm Transorter, no. 6,. 6-65, 9. [7] S.A. Chen, R He, S.L.. Lu and M. Yao, Modeling of air-oered engine based on time coordinate and otimal aroach of gas distribution arameters, Proceedings of the ASME International Design Engineering Technical Conference & Comuters and Information in Engineering Conference, IDETC/CIE, no. 4,. 9-7,. [8] Y.Q. Lian, S.Z. Wang, S.J. Ma, Y.H. Chen and Z.J. Li, Dynamic simulation of the air-oered sash late engine, Chinese Journal of Mechanical Engineering, no. 44,. 4-48, 8. [9] S.A. Chen, S.J. Zhang and R. He, Oerating roerties of reinjection NC air-oered engine, Journal of Traffic and Transortation Engineering, no.,. 5-4,. [] Y. Chen, H. Liu and G.L. Tao, Simulation on the ort timing of an air-oered engine, International Journal of Vehicle Design, no. 8,. 59-7, 5. [] S. Umerujan, T. Gheyret, T. Buso and T. Teruo, Seed control of general-urose engine ith electronic governor, Electrical Engineering in Jaan, no.,. 64-7,. [] Y.Zhang, T. and P.G. Mehta, Feedforard and feedback adative control design and analyses, Proceedings of 4 th IFAC World Congress, , 999. [] Y.H. Tao, Ne Tye of PID Control and its Alication, Beijing: Machinery Industry Press, no., 998, [4] B.D. Wood, Alications of Thermodynamics, Massachusetts: Addison-Wesley Publishing Comany, 98, [5] R.S. Lu, Heat Transfer and Thermal Loading in Internal Combustion Engine, Beijing: Peole s Traffic Press, 988. [6] J.B. Heyood Internal Combustion Engine Fundamentals, Ne York: McGra-Hill Inc, 998. [7] W. Xu, The Modern Design Of Automobile Engine, Beijing: Peole s Traffic Press, 995. [8] S. Menon. N. Moulton and C. Cadou Develoment of a dynamometer for measuring small internal-combustion engine erformance, Journal of Proulsion and Poer, no.,. 94-, 7. [9] D.Y. Xue and Y.Q. Chen Technology and Alication of System Simulation Based on MATLAB/Simulink, Beijing: Tsinghua University Press,. [] B.Z. Yu, Digital Signal Processing, Xi an: Northestern Polytechnical University Press,. [] L. Liu, X.L. Yu, J.Q. Hu and P.L. Chen, Air oered engine design based on Pareto Frontier, Journal of Zhejiang University (Engineering Science), no. 4,. -7, 9. [] H.X. Wu and S.P. Shen, Basis of theory and alications on PID control, Control Engineering of China, no.,. 7-4,. [] Y.J. Lei and S.W. Zhang, Genetic Algorithm Tools and Alications, Xi an: Xi an Electronic Science & Technology University Press, 5. Received: May 6, 5 Revised: July 4, 5 Acceted: August, 5 Caihong et al.; Licensee Bentham Oen. This is an oen access articles licensed under the terms of the Creative Commons Attribution-Non-Commercial 4. International Public License (CC BY-NC 4.) (htts://creativecommons.org/licenses/by-nc/4./legalcode), hich ermits unrestricted, non-commercial use, distribution and reroduction in any medium, rovided that the ork is roerly cited.