GAS INTERNAL COMBUSTION ENGINE WITH INTERNAL MIXTURE FORMATION

Transcription

1 GAS INTERNAL COMBUSTION ENGINE WITH INTERNAL MIXTURE FORMATION Doc.Ing. Scholz Celestýn, Ph.D. Technical University of Liberec, Deartment of vehicles and engines, Hálkova 6, Liberec, tel: , fax: , .: Ing. Brabec Pavel Technical University of Liberec, Deartment of vehicles and engines, Hálkova 6, Liberec, tel: , fax: , .: Abstract Fuel mixture formation inside the cylinder has become more revalent in sark ignition engines in recent years. This concet can be beneficially utilized in gas internal combustion engines where direct injection into an engine cylinder during comression is advantageous not only in increasing volumetric efficiency but also in the elimination of undesired combustion rocess anomalies. This work describes the gas fuel injection arrangements (natural gas or gas fuel mixture) into a cylinder utilized in the laboratory of Technical University of Liberec, Deartment of Vehicles and Engines. The aer deals with both a low-ressure injector design and a highressure injector installation (1 bars) sulied by a secialized roducer. Keywords gas internal combustion engine, direct injection, high-ressure injector, natural gas Shrnutí Tvoření alivové směsi uvnitř válce se v osledních letech oužívá stále častěji u zážehových motorů. Tento koncet lze s výhodou oužít u lynových salovacích motorů, kde římá injektáž do válce motoru během komrese je výhodná nejen z hlediska zvýšení objemové účinnosti, ale i v zamezení nežádoucích anomálií salovací-ho rocesu. Přísěvek oisuje konstrukční usořádání injektáže lynného aliva (zemního lynu, oř. směsi lynného aliva) do válce, která jsou realizována v laboratoři katedry vozidel a motorů Technické univerzity v Liberci. Jedná se jak o konstrukci nízkotlakého injektoru, tak i o zástavbu vysokotlakého injektoru (1 bar) do-daného secialisovaným výrobcem. Klíčová slova lynový zážehový salovací motor, římá injektáž, vysokotlaký injektor, zemní lyn 1. Introduction Currently, there are about 5 million natural gas-oerated assenger and commercial vehicles worldwide. In Euroe, the highest numbers of natural-gas owered vehicles are oerated in Italy, the Ukraine and Germany. According to manufacturer s data the engine ower of natural-gas oerated assenger cars usually corresonds to 85 to 9% of their gasoline owered counterarts. Some manufacturers (e.g. Volvo and Mercedes) reort the identical engine ower for both natural gas and gasoline. Based on fuel utilization, the natural gas engines can be categorized as either single-fuel (natural gas only) or dual-fuel allowing for alternate oeration on either natural gas or gasoline. The single-fuel engines are rimarily used for buses, commercial vehicles and owered industrial trucks. The dual-fuel engines find their rincial alications in assenger cars: in certain cases the gasoline oeration serves for emergencies only.

2 . Mixture Formation Methods The air and fuel mixture formation (rearation) reresents an imortant art of the engine working cycle which imacts the mixture behavior with controlled ignition and the resulting combustion rocess. In rincile, there are two concets of the mixture rearation: internal and external. The external mixture formation reresents the simlest concet. An automobile gas oerated engine can be equied with a fuel system incororating a gas and air mixer in the engine intake manifold or with gas injection into the engine intake by means of solenoids sequentially controlled for each cylinder. The mixer in the engine induction causes a ressure loss, and is, as a result, less suitable comared to injectors. Figure 1: An examle of a gas fuel system arrangement with external sequential natural gas injection [4] Obrázek 1: Příklad usořádání lynového alivového systému s vnější sekvenční injektáží zemního lynu [4] The internal mixture formation with the gas fuel injection directly into a working cylinder sace is a more comlex concet to develo and construct. The searation of fuel from air during the cylinder charge exchange eliminates back fires in the induction system, the achievable heat value increases and, consequently, the engine ower grows. Deending on the injector inlet ressure two imlementations of the concet can be distinguished: one using low-ressure injection and the other involving highressure injection. Low-ressure injection with gas ressure below MPa requires a longer duration and at high load the injection commencement must occur during the induction stroke, i.e. at the time when the inlet valve is oen. High-ressure injection with gas ressure between 1 and 1 MPa currently reresents the most u-todate and efficient concet of an internal mixture formation eliminating adverse combustion anomalies and benefiting from a stratified mixture formation in combination with lean mixture. In order not to restrict vehicle range high storage ressure has to be imlemented. The fuel rails (storage containers/storage cylinders) accommodating 7 MPa ressures are develoed by Dynetek Euroe [1].

3 3. High Pressure Injection To verify the advantages of and benefits from the high ressure injection of gas directly into an engine cylinder, a new testing bench is resently being reared in the Piston internal combustion engine laboratory (Technical University of Liberec, Deartment of Vehicles and Engines). With this roject, our laboratory extends the research rograms to the area of the internal mixture formation for small engines designed for assenger cars; namely a three-cylinder internal combustion engine having a total dislacement of 1. dm 3. Figure: Test bench with gas engine (total dislacement of 1. dm 3 Obrázek : Zkušební stanoviště lynového motoru o objemu 1. dm 3 The engine concet is based on new high-ressure injectors with 1 MPa inlet ressure. At the moment, our laboratory uses injectors roduced by Hoerbiger Valve Tec (the injectors have been develoed within the Euroen rogram HylCE). After being installed in a three-cylinder, 1. dm 3 engine, with the gas inlet ressure of 1 MPa and the cross-sectional area of flow of 1 mm, these high-ressure injectors (see Fig.3) shorten the injection duration to a maximum 5 of the crank angle. Consequently, even at maximum ower, the injection can be timed in the comression stroke only after the intake valve closes. The electronic system for the controlling and monitoring of engine oeration has been sulied by ADCIS Comany. The high-ressure injector nozzles are shown in Fig.4.

4 Figure 3: High-ressure injector sulied by Hoerbiger Valve Tec [] Obrázek 3: Ukázka vysokotlakého injektoru od firmy Hoerbiger Valve Tec [] Injector Ti Geometry 6 holes total no central hole equal 6deg orientation 9 deg cone incl. angle (each hole 45 deg from injector axis) holes sized to meet existing flow secifications Figure 4: High-ressure injector sulied by Hoerbiger Valve Tec [] Obrázek 4: Tryska vysokotlakého injektoru od firmy Hoerbiger Valve Tec [] 9 deg

5 4. Injection Parameter Comutation The following injection arameter comutations concentrate on the establishment of the gaseous fuel mass flow rate and valve exosure time. Universal gas constant Molar mass R 1 = 8314J kmol K M fuel = 16 kg kmol Secific gas constant r R M 1 = = 519,65J kg K fuel Poisson s ratio κ = 1, 4 Effective min. cross section Inlet temerature ( C) Inlet ressure (bar) Outlet ressure (bar) A = 6 1mm = 1 1 m T = 37 C 31K = = 1bar = 1 1 = 3bar = Pa Pa Critical ressure ratio = =, 58 κ + 1 kr Actual ressure ratio =, 3 κ κ + 1 Flow in a minimal cross section will be critical if kr <, otherwise it is subcritical. κ + 1 κ κ Flow coefficient critical ψ = =, 484 κ + 1 Mass flow of gas subcritical ψ = κ κ κ κ + 1 κ 1 m fuel = A ψ =,175kg s = 17,5g s = 61, 38kg h T r Maximum injected quantity Injection angle CA = 5 oen Engine seed n = 45 min CAoen 1 Injection duration toen = = 1, 85ms 36 n m fuel 1 Injected fuel quantity m = CAoen = 31, 36 n inj 57 mg

6 The selection of the injector necessitated a study of the engine head design modifications required for its installation. The work was far from easy due to the considerable dimensions of the selected injectors (in roortion to the 1. dm 3 engine head size). In conducting these modifications we strove to comly with the following conditions: simle but reliable design conveniently chosen direction of gaseous fuel injection minimal imact on engine head cooling (water ort constriction) no interference with the sace for lubricating oil no reduction in the suction ort cross section At resent, this selected engine head design modification with the concurrent installation of injectors is in the rocess of roduction. The installation of injectors is shown in Fig.5. A general view of the fuel suly to injectors from a rail resently under consideration can be seen in Fig.6. Fig.7 shows an axis geometry of jets injected out of the standard injector nozzle (Fig.4). Figure 5: Position of a high-ressure gas injector in the internal combustion engine head Obrázek 5: Umístění vysokotlakého injektoru lynu v hlavě salovacího motoru

7 Figure 6: View of the fuel suly to injectors from a rail under consideration. [5] Obrázek 6: Pohled na uvažovaný řívod aliva k injektorům ze zásobníku (railu). [5]

8 Figure 7: View of axis geometry of jets out of the injector. Obrázek 7: Pohled na geometrii os arsků z injektoru. 5. Conclusion The utilization of internal mixture formation may grant advantages in terms of the ability to control the combustion rocess and gaseous emission generation. Resecting the engine design, however, the alication of the internal mixture formation is more demanding due to the installation of the injectors into the cylinder head. At the resent time, the above rocess is being used in research rojects focused on the utilization of hydrogen in internal combustion engines. It will certainly be useful to know all the benefits of this u-to-date method of mixture formation even for engines fueled by natural gas even if this aroach calls for significant rearrangements concerning vehicle storage caacity and refueling infrastructure as well. Research and exerimental work will be commenced in the laboratory of Technical University of Liberec at the end of 7. Acknowledgements

9 Published results were acquired using the subsidization of the Ministry of Education and Science of the Czech Reublic, roject 1M68477 Josef Božek Research Center of Engine and Automotive Engineering. References [1] RAU, S.: Comressed Hydrogen Storage for Vehicle Alications. In.: 1st Hydrogen Internal Combustion Engines. TU Graz, Graz 6 [] Data and Materials acquired from Hoerbiger Valve Tec, Vienna 6 [3] ŠIMAN, J.: Build in high ressure injector for gas fuel into engine 1. dm 3. Diloma work, KVM 351, Technical University of Liberec, 7 [4] LAURIN, J. HOLUBEC, R. MAREŠ, H.: Develoment of a gas engine for assenger cars. In.: XXXVIII. International Conference of Deartments and Work-laces focused on internal combustion engines, Bratislava ISBN