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Technical Paper

Predictions for Nucleate Boiling - Results From a Thermal Bench Marking Exercise Under Low Flow Conditions

Two predictive methods have been applied to an IC engine cooling gallery simulator to provide benchmarking heat transfer information. The object of this work was to assess the suitability and accuracy of these methods for application to future on-engine heat transfer studies. Such studies are aimed at developing predictive tools to aid in the design of precision cooling systems. The modelling techniques of Rohsenow and Chen have been used, modified and validated. Compared against experimental data, the sub-cooled form of the Chen model has been found to be most representative for the cooling gallery simulator designed specifically to meet the requirements of this work.
Technical Paper

Actively Controlled Cooling Jets

A proof-of-concept study has been undertaken to demonstrate the use and potential benefits of actively controlled coolant jets in an IC engine cooling gallery simulator. Results have shown that substantial reductions in coolant volumes are possible and that the control of the liquid/metal surface temperature can be achieved within +/- 0.2°C in response to transient heat flux conditions.
Technical Paper

Front End Auxiliary Drive (FEAD) Configurations Focusing on CO2 Benefits

An experimental investigation, using a Design of Experiments approach, has sought to quantify the potential CO2 savings that could be made by the electrification of certain mechanical devices as part of the Front End Auxiliary Drive (FEAD) on a 2.4 litre DI diesel engine. The experiments considered the electrification of the cooling fan; power assisted steering system, and the vacuum pump. A number of different build configurations have been evaluated on a dynamic testbed over the New European Drive Cycle (NEDC). The overall conclusion is that the move towards electrification of the devices listed would result in a 6-7% saving in CO2 over the NEDC. These benefits however, need to be considered alongside other issues such as increased on-cost, more control complexity and reliability implications of adopting electrically driven devices.
Technical Paper

On-Vehicle Controllable Cooling Jets

A study has been undertaken to demonstrate the use and potential benefits of actively controlled coolant jets in a vehicle. Results have shown that active control of cooling jets has the potential to regulate the temperature of thermally critical areas of the cylinder head, in this case the exhaust valve bridge. In addition the temperature gradient across the head from the exhaust valves to the inlet valves is directly influenced. These capabilities offer improved control of the combustion process and enhanced durability. Furthermore the system allows heat to be rejected at much lower overall coolant flow rates than with a conventional arrangement. The technique relies on an adequate supply of coolant at a lower temperature than that within the engine and on the availability of a suitable measurement technology within the thermally critical region. Unlike passive precision cooling the active jets allow optimization of the cooling at all engine speed / load points.
Technical Paper

The Design, Construction and Testing of a Non Air-Breathing Diesel Engine Research Facility for Autonomous Underwater Vehicle Applications

Closed and recycle diesel engine systems have been developed for use on board conventional manned military and commercial submarines. This type of power system is now being considered for unmanned Autonomous Underwater Vehicle (AUV) applications. However, with a simple recycle system, the recirculated carbon dioxide rich combustion products can be expected to have an adverse effect on engine performance. Recent developments in this field have been concerned with producing synthetic atmospheres whose properties match those of free air so enabling the non air performance at least to match that of the normally aspirated unit. This philosophy has resulted in bulky and complicated exhaust gas management systems. The possibility of a diesel engine operating on a carbon dioxide/oxygen atmosphere whilst still retaining acceptable engine operating performance would therefore seem to require further examination.
Technical Paper

A Review of Precision Engine Cooling

Although successful “precision cooled” prototype engines have been demonstrated, the design of most mainstream coolant jackets has evolved only cautiously, and lacked this major change in approach. The achievements and potential of precision cooling are reviewed, along with an extension into nucleate boiling based heat transfer. It is demonstrated that ideas for advanced “external” cooling systems with low flowrates are in fact extremely compatible with the “internal” precision engine cooling philosophy, and in combination promise even larger benefits.
Technical Paper

“Nucleate Boiling Investigations and the Effects of Surface Roughness”

The findings presented in this paper are part of a long term project aimed at raising the science of heat transfer in internal combustion engine cooling galleries. Initial work has been undertaken by the authors and an experimental facility is able to simulate different sizes of coolant passages. External heat is applied and data for the forced convective, nucleate boiling and transition or critical heat flux (CHF) regimes has been obtained. The results highlighted in this paper attempt to quantify the effects of cooling passage surface roughness on the nucleate boiling regime. Tests have been conducted using aluminium test pieces with surface finishes described as smooth, intermediate and as-cast. It has been found that the as-cast surface increases the heat flux density in the nucleate boiling region over that of the smooth and intermediate surfaces.