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An internal-combustion engine platform that may operate on a portfolio of cycles for increased engine expansion ratio, combustion under constant volume, variable compression ratio, and cold start is introduced. Through unique thermodynamic cycles, the engine may be able to operate on a much greater expansion ratio than the compression ratio for a significantly improved thermal efficiency. This improvement is attained without involving a complex mechanical structure or an enlarged engine size, and at the same time without reducing the compression ratio. The engine with these features may serve as an alternative to the Atkinson cycle engine or the Miller cycle engine. Additionally, based on the same engine platform, the engine may operate on other cycles according to the load conditions and environmental considerations. These cycles include those for combustion under constant volume, variable compression ratio under part load conditions, and cold start for alternative fuels.

A novel mechanism for the cold start of internal combustion engines is described in this paper. The cold-start mechanism is based on a modified prechamber configuration by adding a chamber valve to the prechamber, which could establish or block the communication of the prechamber with the cylinder space. The cold-start procedure includes a stroke that conserves the energy content of the first compressed charge through expansion against a low-pressure environment, and a subsequent recompression stroke to compress the charge to a much higher temperature. An analytical evaluation on the cold-start process is undertaken, and it is found that the charge could be compressed effectively to a temperature above the ignition temperature of ethanol or methanol. The same engine configuration may also enable combustion under a closed-chamber condition and is employed during the engine warm-up process to reduce excessive hydrocarbon emissions due to incomplete combustion.

A heat transfer device which employs a solenoid-operated reciprocating mechanism for driving liquid from the condenser section to the evaporator section is described. The heat transfer device is coined as the reciprocating-mechanism driven heat loop, which includes a hollow loop having an interior flow passage, an amount of working fluid filled within the loop, and a solenoid-operated reciprocating driver. The hollow loop has an evaporator section, a condenser section, and a liquid reservoir. The reciprocating driver is integrated with the liquid reservoir and facilitates a reciprocating flow of the working fluid within the loop, so that liquid is supplied from the condenser section to the evaporator section under a substantially saturated condition and the so-called cavitation problem associated with a conventional pump is avoided. Experimental study has been undertaken for a proof-of-concept solenoid-operated heat loop for high heat flux thermal management applications.

Piston design that incorporates the heat pipe cooling technology may provide a new approach for piston-temperature control. A simulated piston crown that contains an annular reciprocating heat pipe is developed to investigate the effect of heat pipe cooling on the piston crown temperature distribution. For this purpose, a reciprocating engine testing apparatus is designed and constructed. The experimental study focuses on the static and dynamic operational characteristics of the heat pipe and its cooling effect on the simulated piston crown under different power input. The experiment results indicate that a piston crown incorporating a heat pipe can yield a uniform temperature distribution in the ring-bank area of the piston crown. The testing results would also provide the needed information for a possible piston design that incorporates the heat pipe cooling technology for improved thermal-tribological performance.

The first part of this series of papers reports the development of a simulated piston crown with an annular reciprocating heat pipe and the investigation on the effect of heat-pipe cooling on the piston-crown temperature distribution. This paper presents the modeling of the simulated piston crown with the finite-element method and the analysis of its thermal performance. The heat-transfer coefficient with respect to the reciprocal environment of the experimental apparatus and the effective thermal conductance of the annular heat pipe are determined by correlating the modeling with the experimental measurements. The numerical modeling agrees well with the experimental results. The analyses indicate that the heat-pipe cooling technology can provide an effective means for piston temperature control.

An engine piston cooling method incorporating shaking-up heat pipes (SUHPs) is described. In shaking-up heat pipes, the liquid return from the condenser to the evaporator section is achieved by a high-frequency shaking-up action. In addition, the liquid splash and impingement on the inner surface facilitate temperature uniformity along the heat pipe. The concept of the SUHP is verified by experimental observation of a transparent heat pipe and thermal testing of a copper/water SUHP. A comparative thermal analysis on the SUHP and gallery cooling systems is performed. The approximate analytical results show that the piston ring groove temperature can be significantly reduced using the heat pipe cooling technology, which may contribute to an increase in engine thermal efficiency and a reduction in environmental pollution.

An increase in the temperature of charge in an engine combustion chamber is now more and more attractive due to its advantages in energy savings and environmental control. However, this will affect the design of engine elements, since a higher temperature will result in considerable thermal stresses and distortion, material and lubricant degradation, or even seizure and scuffing failures. Actually even for currently designed diesel engines, engine piston assembly failure, particularly piston ring/cylinder liner interface failure due to heat accumulation, is a very serious problem. Effective means of carrying heat away from this area are crucial for the prevention of scuffing. However, due to the reciprocal motion of the mechanism, efficient piston cooling is difficult to achieve using conventional cooling methods.