Hot gas engine combustion chambers
United States Patent Hakansson et al.  
 [ 1 Apr. 22, 1975 HOT GAS ENGINE COMBUSTION CHAMBERS Inventors: Sven Anders Samuel Hakansson,  
 Malmo; Mats Inge Moritz, Trelleborg. both of Sweden Assignee: Kommanditbolaget United Stirling (Sweden) AB &amp; Co., Malmo, Sweden Filed: May 24, 1973 Appl; No.: 363,628  
 Foreign Application Priority Data June 7. 1972 United Kingdom 26523/72 u.s. c1. 60/517 1m. c1. F02g 1/04 Field of Search 60/517, 519. 524, 523;  
 Primary E.\&#39;an1i/1erMa1&#39;tin P. Schwadron Assistant E.tan1iner-H. Burks, Sr. Attorney, Agent, or FirmLaurence R. Brown [57] ABSTRACT To facilitate cold starting with low grade fuels a Stirling type engine has a spark plug fuel igniter critically spaced between a fuel atomizer and the engine heating pipes so that it does not foul or misfire.  
 1 Claim, 1 Drawing Figure 1 HOT GAS ENGINE COMBUSTION CHAMBERS This invention relates to a hot gas engine combustion chamber of the kind (herein called the kind defined&#34;) comprising walls bounding the chamber, a fuel atomizer mounted in or on one of said walls, heat transfer surfaces for transferring heat to the working gas of the engine and extending into or contained within the chamber between said walls, and a spark plug having a spark gap for igniting the fuel atomized by the atomizer.  
  During the development of combustion chambers of the kind defined it has been difficult to ensure rapid and reliable ignition of the fuel when the temperature in the combustion chamber is low and the fuel is ordinary diesel oil, which is the most readily available lowcost fuel. Generally the spark plugs have been located quite close to the fuel atomizers, and in order to ensure a reliable ignition the spark plugs have been specially designed to avoid being clogged up by soot, or the ignition systems have been specially designed to cause sparks even when substantial amounts of soot have been collected across the gaps.  
  In spite of these attempts, the starting of a hot gas engine with a combustion chamber of the kind defined has still been difficult and involved substantial smoke emissions because of problems with the ignition in the combustion chamber.  
  The present invention is therefore intended to provide a combustion chamber of the kind defined in which diesel fuel may be ignited almost instantly even when the engine is cold and by means of a spark plug of conventional design used in a conventional ignition system.  
  According to the present invention a combustion chamber of the kind defined is characterised in that the spark gap of the spark plug is located between the atomizer and the heat transfer surfaces at a distance from the atomizer which is longer than the distance between the spark gap and the part of the heat transfer surfaces which is nearest to the spark gap.  
  How the invention may be put into practice is described in more detail with reference to the accompanying drawing, showing schematically a vertical section through a hot gas engine provided with a combustion chamber according to the invention.  
  The hot gas engine shown comprises a housing 1 carrying several cylinders 2 and regenerator-cooler units 3 (only one of each being shown in the drawing). Each cylinder contains a piston 4 with a piston rod 5 which is connected through a cross-head 6 and a connecting rod 7 to a crank-shaft 8. The piston 4 separates two charges of working gas. The charge located above the piston shown is connected through pipes 9 constituting heat transfer surfaces to the top of a regenerator-cooler unit not shown. The charge located below the piston shown is connected through a duct 10 to a cooler 11 and a regenerator 12 of the unit 3. From the top of the said unit 3 the gas of said charge may pass to the top of&#39;a cylinder (not shown) through pipes 13 similar to the pipes 9.  
  The said pipes 9 and 13 extend into or are contained within a combustion chamber 16, between walls 14 and 1S bounding the centrally arranged combustion chamber 16. The wall 14 is composed of frusto-conical parts, and a fuel atomizer 17 is centrally mounted therein. A spark plug 18 having a spark gap 19 protrudes into the chamber 16, the gap 19 being located at a distance from the atomizer 17 which is longer than the distance between the spark gap and the part of the heat transfer surface of the pipe 13 which is nearest to the spark gap 19.  
 The spark plug 18 is connected to a conventional ignition coil 20.  
  The engine shown is of the double-acting type in which each charge of working gas is exposed to heating, expansion at high temperature, cooling and compression at low temperature in a cycle wherein, for example, the expansion is degrees ahead of the compression in a four-cylinder engine.  
  The heating of the working gas charge is caused by hot combustion gases generated in the combustion chamber passing between the pipes 9 and 13 and heat from the combustion gases being transferred through the walls of the pipes to the working gas flowing inside the pipes.  
  The ignition of the fuel atomized by the atomizer 17 is caused by sparks across the gap 19. The location of the said gap 19 at a comparatively long distance from the atomizer 17 compared with the size of the combustion chamber (which size may be measured as the distance between the atomizer l7 and the pipes 9 and 13) ensures that the fuel has been sufficiently vapourised before reaching the ignition sparks. Previously it has been the usual technique to locate the spark gap very close to the atomizer and to use boosted sparks for the ignition. The arrangement according to the invention has proved in tests to be very reliable even after many starting operations and after many running hours of the engine.  
 What we claim is:  
  l. A hot gas engine combustion chamber of the kind comprising walls bounding the chamber, a fuel atomizer mounted in or on one of said walls, heat-transfer surfaces for transferring heat to the working gas of the engine and extending into or contained within the chamber between said walls, and a spark plug having a spark gap for igniting the fuel atomized by the atomizer, characterised in that the spark gap of the spark plug is located between the atomizer and the heat transfer surfaces at a distance from the atomizer which is longer than the distance between the spark gap and the part of the heat transfer surfaces which is nearest to the spark gap.