Life limiting properties of a superalloy in a low heat rejection engine

The objective of low heat rejection engine (LHRE) technology is to reduce the heat transfer from the gases in the combustion chamber to the cooling medium by insulating the combustion chamber. Doing so can increase the temperature during combustion, resulting in higher work output or higher exhaust gas temperatures. The higher exhaust energy can be potentially recovered by turbocharging. Thus LHRE technology offers the potential for gains in fuel efficiency, decrease in the size of cooling systems, the use of alternative fuels, and reduction of certain components of exhaust emission. Many experimental efforts to develop LHRE's using ceramic materials have been undertaken and are discussed in the literature. In this research, two major problems have been identified which need to be overcome: (1) the need for high temperature lubrication, and (2) the brittleness of the ceramics used to achieve the high temperature in the engines.; To overcome the limitations of the current LHRE designs, this dissertation presents a novel design concept using a superalloy as the combustion surface and using currently available lubrication techniques. In this design, an extended piston top and a liner are designed and installed in an existing one cylinder Diesel engine. HAYNES{dollar}circler{dollar} 230{dollar}rmsp{lcub}TM{rcub}{dollar} superalloy is used as the combustion surface instead of using ceramics, thus eliminating the problem of brittleness associated with ceramics in LHRE's. Between the piston top and the cylinder liner, there is a carefully designed clearance so that there will be no contact between them during engine operation. The piston top is insulated from the main piston body by a ceramic gasket, and therefore the piston and crankcase portions of the engine operate at nearly normal temperatures which eliminates the need to incorporate a high temperature lubrication system in this design.; The design concept was studied both analytically and experimentally including 1001 hours of engine operation. The scope of this dissertation is as follows: (1) A literature survey of the previous work in LHRE's; (2) A finite difference analysis of the piston top heat transfer; (3) The design and construction of the Low Heat Rejection Diesel Engine; and (4) The testing of the engine for 1001 hours and the assessment of the effects of the engine operating environment on the superalloy piston top.; This research has demonstrated a viable design which addresses the most challenging obstacles to the development of successful LHRE's. It was shown that HAYNES{dollar}circler{dollar} 230{dollar}rmsp{lcub}TM{rcub}{dollar} served successfully as a combustion surface material during 1001 hours of engine operation at temperatures above 650{dollar}spcirc{dollar}C. It was also shown that the material survived with little or no wear or degradation of microstructure under the combustion chamber operating conditions. The research indicates that HAYNES{dollar}rmcircler 230sp{lcub}TM{rcub}{dollar} has significant technical viability as a combustion surface material for LHRE application. The insulation between the piston top and the main piston body served effectively to insulate the lower temperature base of the engine from the high temperature combustion chamber. As a result, the standard lubrication system in the test engine was found to provide adequate lubrication for the engine during LHRE operation.