Combustion control is a significant topic for achieving high efficiency and low emissions of internal combustion engines. Recently, in-cylinder pressure sensor-based closed-loop control strategies have become the preferred solution. However, their practical applications in automotive industries are limited due to the intensive acquisition of pressure series for a whole cycle and subsequent calculation of combustion indicators. This paper proposes a method for in-cylinder pressure information extraction and combustion phase estimation of spark ignition (SI) engines based on pressure measurements at several points coordinated by the crank angle. First, nonlinear dynamics analysis is introduced to analyze the system of in-cylinder pressure evolution, which is proved to be a deterministic nonlinear dynamic system with chaotic characteristics. Then, a 3-dimensional system state variable is determined to replace the pressure series during combustion. Second, with the determined system state variable, the in-cylinder pressure series during combustion and the combustion phase are learned and estimated by a machine learning method, namely, extreme learning machine (ELM). As a result, only pressure measurements at 3 points and ELM estimation models are required, instead of intensive data acquisition and calculation. The experimental validations carried out on a gasoline engine test bench have proved that the reconstruction and estimation results are accurate and that the method can perform well in real-time combustion control.

The surface temperature measurement is susceptible to the surrounding air for the cable or the insulated busbar laid in free air. Therefore, an approach for improving their surface temperature measurements by covering the temperature sensor with a heat insulated layer is put forward. Firstly, the surface temperatures of the cable and the insulated busbar attached by a platinum resistance thermometer with and without a heat insulated layer under rated current are obtained using the thermal analyses in Comsol. Subsequently, the temperature rise test of the insulated busbar was carried out for the indirect verification of the previous analyses. The measured surface temperatures were used to calculate the conductor temperature based on the transient thermal network. By comparison with the measured conductor temperature, it is found that the deviation of the surface temperature measurement without the heat insulated layer is about 4~7 K while that with the heat insulated layer is only ±1 K. Further, the generalization of the presented method to the distributed temperature sensing system is analyzed. This study demonstrates that the accuracy of the surface temperature measurement of the cable and the insulated busbar can be effectively improved by wrapping a suitable heat insulated layer around the sensor.

The dynamic behavior, especially in the transition to oscillation mode (in-phase and anti-phase), of two interacting non-premixed methane-air jet flames was investigated experimentally. A well-controllable experimental system for the present purpose was constructed and key parameters; such as fuel flowrate (Q), burner diameter (d), and burner separation distance (L), were varied systematically. A well-known periodic motion of the flame was observed and the frequency monitored by thermocouples mounted adjacent to the burner exit. Time-variation of flame shape was recorded by a high speed camera associated with the optical imaging visualization. It was found that the flickering frequency was insensitive to the fuel flowrate, Q, implying that inertia played secondary role in the transition. Instead, the burner critical separation distance for the transition (L_crt) varied when various burner diameters were used, confirming that the difference in distance played an important role in the transition. It was found that the critical condition could be summarized by an updated correlation as d × L³_crt~const. This is slightly different from the one recently proposed by Yang et al. (2019), which was given under a narrower range of the fire scale. Accordingly, the critical condition can also be described by the critical value of the updated global parameter, such as α³Gr^4/3, where α and Gr denote the length ratio (L_crt/d) and Grashof number based on the burner diameter, respectively.

Corrugated louver fin, which has louvers on wavy surface, may be a promising mean to augment the air-side heat transfer of fin-and-tube heat exchangers. However, only limited prior studies are available. In this study, two kinds of corrugated louver fin-and-tube heat exchangers – one having one corrugation per row and the other having two corrugations per row – were tested, and the results were compared with those of the standard louver fin and the plain fin samples. The highest j and f factor were obtained for the standard louver fin sample, followed by the single corrugated louver fin, the double corrugated inclined louver fin and then the plain fin sample. The high j and f factor of the standard louver fin sample may be due to the large louver fraction on the fin surface. Furthermore, larger fin surface area of the double corrugated louver fin compared with that of the single corrugated fin may be the reason for the smaller j and f factor. All the enhanced fin samples yielded larger heat transfer capacity than the plain fin sample at the same pumping power. Furthermore, the largest heat transfer capacity per pumping power was obtained for the standard louver fin sample. The single corrugated louver fin sample yielded higher heat transfer capacity per pumping power than the double corrugated sample.

In this study, two kinds of corrugated louver fin-and-tube heat exchangers – one having one corrugation per row and the other having two corrugations per row – were tested under wet condition, and the results were compared with those of the standard louver fin and the plain fin samples. The highest j and f factor were obtained for the double corrugated louver fin sample, followed by the single corrugated inclined louver fin sample, the standard louver fin sample and then the plain fin sample. This result is in contradiction with those obtained under dry condition, where the standard louver fin sample yielded the highest j and f factor. The high j and f factor of the corrugated louver fin sample may be due to the improved condensate drainage over the standard louver fin sample. Corrugated channels along with louvers of high louver angle of the corrugated louver fin samples appear to have resulted better condensate drainage. All the enhanced fin samples yielded larger heat transfer capacity than plain fin samples at the same pumping power. Furthermore, the largest heat transfer capacity per pumping power was obtained for the double corrugated louver fin sample, followed by the single corrugated louver fin sample and then the standard louver fin sample.

In this study, we experimentally evaluated heat transfer performance using a configuration of layered parallel microchannels, with a focus on the effect of refrigerant mass flow rate on heat transfer performance. HFC-245fa was used as a refrigerant owing to its chemical stability and appropriate saturation pressure for the design of the cooling system under actual conditions. Experimental results showed that heat transfer rate and heat transfer coefficient increased with increasing refrigerant mass flow rate under the same superheat. However, the maximum heat transfer coefficient reached a certain value even as the mass flow rate increased. Further, on comparing the experimental results with numerical ones performed in this study, it was confirmed that the heat transfer performance with the configuration of layered parallel microchannels depended on the thermal resistance between each layer. Furthermore, to realize the maximum potential of the heat sink with the layered parallel microchannels, it was important to prevent a decrease in wall superheat at the channels on the far side from the heat source. Eventually, in the series of experiments, a heat flux of 3.04×10⁶ W/m² and a heat transfer coefficient of 5.20×10⁴ W/(m²∙K) were reached at a pressure drop of 48.4 kPa under a mass flow rate of 3.33×10^-2 kg/s. This was achieved despite the use of a simple configuration for heat transfer enhancement and a refrigerant having poor latent heat dissipation.

Owing to their large surface area and capillary effect, porous materials are highly desired for heat-transfer applications. In this study, we investigated the evaporation behavior of a water droplet on porous epoxy resin with a three-dimensional network structure. As the material existed in the liquid state before sintering, it could be easily converted into a porous body on a heating surface. The material showed a pore size of 0.15 μm and a porosity of 50%. First, the evaporation behavior of a water droplet placed on the surface of this porous body was investigated. It was found that the evaporation rate increased when the evaporation was carried out on the surface of the porous body. Then, a vapor chamber experiment was carried out with the porous material. The porous body acted as the generating surface and its heat transfer performance was estimated. The cooling performance of the porous body was 1.2 times higher than that of the non-porous material.

This paper presents 3D numerical investigation of the turbulent flow and heat transfer characteristics of a twisted square duct installed with multi-twisted tapes. Air was used as the working fluid with flow rates in terms of Reynolds numbers ranging from 3000 to 20,000. The effects of (1) multi-twisted tape width ratios (w/H) of 0.2 to 1.0 and (2) the number of channels (N = 2 and 4) on heat transfer and flow mechanisms were studied at constant twist ratio of y/D = 3.5. The numerical results showed that twisted square duct combined with twisted tape caused swirl flows which effectively promoted fluid mixing and provided heat transfer over those of both a straight smooth square duct and twisted square duct. Increasing w/H led to increases in both heat transfer and the friction factor. At a given multi-twisted tape width ratio (w/H), the heat transfer and friction factor with N = 4 were higher than those with N = 2, while thermal enhancement factor showed the opposite trend. A maximum thermal enhancement factor of 1.93 was obtained at tape width ratio of w/H = 1.0, channel number of N = 2 and Re = 3000.

The objectives of this study were to: (i) build simulation model for mult-unit air conditioning (AC) system with digital scroll compressor (DSC) and validate its precision by experiments; (ii) build system energy consumption calculation model by simulation. Lumped parameter model of compressor and electronic expansion valve, and district lumped parameter model of condenser and evaporator were employed in simulation program of multi-unit AC system with DSC. The results indicated that errors between simulated value and experimental data of system hourly energy consumption were within 10%. The simulation model showed good precision. Simulation results indicated that system hourly energy consumption differences caused by indoor unit operating number were less than 15%, which can be neglected. Thus, hourly energy consumption (HW), hourly energy efficiency ratio (HEER) and hourly heating performance factor (HHPF) calculation model of multi-unit AC system with DSC were built based on simulation results. Simulation results indicated that the variation of HW with part load ratio (PLR) and outdoor air temperature presented concave surface distribution and the variations of HEER and HHPF with PLR and and outdoor air temperature presented convex surface distribution. The model provides a tool for energy saving optimization and seasonal energy consumption evaluation of multi-unit AC system with DSC.

Condensation of fluid molecules on a solid surface with and without a structure at the nanometer scale was simulated by means of the classical molecular dynamics simulations. We investigated effects of the nanostructures and the wettability, on the condensation process and an interfacial thermal resistance on whole surfaces and segments of the surface with the nanostructure. In our calculation system, we employed the fluid system of argon confined between two parallel solid walls, where a cuboid nanostructure was attached to the solid bottom wall. All intermolecular potential functions were the 12-6 Lennard-Jones form. We simulated hydrophobic and hydrophilic conditions by changing the intermolecular strength between the fluid molecules and the solid walls. Our results showed that the droplets tended to be formed at the base of the nanostructure and a droplet formed at the top of the nanostructure, regardless of the interaction strength between the fluid molecules and the solid walls. In addition, the wettability influenced on the contribution of each segment of the nanostructure on heat transfer during condensation. Local interfacial thermal resistance at the top and base of the nanostructure was relatively smaller than those at other segments of the nanostructure at an early stage of the condensation in the case of hydrophobic surface.

The gaseous fuel-air coaxial jet flow and combustion under different fuel compositions are actively controlled through periodic excitation of the initial jet shear layer with arrayed miniature jet actuators equipped on the inner surface of the annular nozzle. In the present study, methane (CH₄) is diluted by nitrogen (N₂) or carbon dioxide (CO₂) with various dilution rates to mimic biogas with different ratios of combustible and non-combustible components. The spatio-temporal development of the controlled jets are examined with phase-locked two-component particle image velocimetry (PIV). Firstly, it is found that the large-scale vortical structures and the associated mixing in the cold coaxial jets are flexibly controlled by changing the injection frequency f_v of the miniature jets even for the different fuel dilution rates, which affect the momentum flux ratio of the coaxial jet. Based on the cold jet experiments, the present control scheme is applied to bluff-body held coaxial jet flames. The flame holding and emission characteristics for the controlled flames are evaluated under different dilution rates. It is demonstrated that the blow-off limits of the controlled flames are significantly extended to higher dilution rate as increase in f_v. Moreover, carbon monoxide (CO) emission for different fuel dilution rates can be improved by manipulating the mixing upstream of the flame base. At low dilution rate, CO emission is drastically reduced through the enhanced mixing by the intense vortices, which realize highly-oxygenated combustion. On the other hand, at high dilution rate, low CO emission can be achieved through the local mixing enhancement near the inner shear layer by the weak vortices, which lead to relatively high temperature combustion.

In this study, we quantitatively discuss several kinds of thermal resistances that rise up to the surface in thermal management of automotive SiC-based on-board inverters with extremely high heat flux of 500 W/cm². It is proven that a stacking structure without a heat spreader and a direct cooling method utilizing two-phase immersion cooling technique can provide a breakthrough as the key technology. Furthermore, it is verified that a two-phase immersion cooling technique using “breathing phenomenon” spontaneously induced by a lotus copper jointed onto a grooved heat transfer surface can realize both the above-mentioned stacking structure and extremely high critical heat flux beyond 500 W/cm² in a saturated pool boiling environment (534 W/cm² at the maximum).