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Abundant alcohols, including ethanol, propanol, butanol, and pentanol, are expected to be used in compression ignition engines to ease the shortages of fossil fuel. The various alcohols have quite a different combustion and emission characteristics in the engine due to the changes in molecular structures. In this paper, a series of experiments were conducted on a modified common-rail diesel engine fueled with diesel/alcohols blended fuels in a wide operating range. The effects of alcohol chain length, oxygen content, and molecular structure on engine combustion and emission characteristics are studied systematically. The experimental results show that the blending of alcohols increases the peak values of in-cylinder pressure and maximum pressure rising rate. Besides, the combustion duration and ignition delay are mainly affected by oxygen content and isomer structure. The addition of short-chain alcohols will significantly reduce the total mass of particulate matter (PM) emissions, while the CO and HC emissions increase appropriately. The CO, HC, aldehydes, and ethylene emissions are mainly affected by carbon chain length and isomer structure. For PM emissions, the carbon chain length, molecular structure, and oxygen content of alcohol fuels have different influences on PM number, PM mass, and particle size distributions. The shorter carbon chain of alcohol leads to smaller particle size, and higher oxygen content leads to lower total particle mass.

The dual direct injection strategy can flexibly control the reactivity distributions and equivalence ratio, which shows a great potential in realizing clean and efficient combustion. However, the sprays’ collision is inevitable when the fuel sprays are injected into the combustion chamber simultaneously owing to limited in-cylinder space, which is rarely investigated. The investigation aims to explore the atomization and combustion characteristics of collision between biodiesel and butanol sprays at different injection delay times of biodiesel (0, 0.5, 1, 1.5, 2 ms). Experiments are conducted in a constant volume combustion chamber. The collision spray and combustion images are captured by optical diagnosis techniques. Several macroscopic parameters are obtained, including spray behavior, spray area, ignition delay, ignition location, flame behavior, flame lift-off length, and natural luminosity intensity. Results show that the variation of injection delay time can effectively change the spray distribution and realize the concentration stratification. The liquid-phase diffusion region increases with an increased premixed charge of butanol spray, but the total evaporation time has a tiny difference. The sprays’ collision can promote the ignition process, but the ignition location is slightly affected by the injection delay time of biodiesel. A trade-off relationship between the vapor-phase diffusion area and combustion characteristics is found. When the injection delay time exceeds 0.5 ms, a longer injection delay time can lead to a larger vapor-phase area, which causes smaller equivalent ratio, longer flame-off length, and lower luminosity intensity. However, a longer injection delay would lead to an uncomplete combustion of the n-butanol spray. At the experimental cases, the injection delay time of biodiesel should be 1/2–2/3 injection duration to realize complete combustion and small emissions.

This research work studied the mode switching between ICCI low temperature combustion and conventional CI combustion in a single-cylinder diesel engine. The combustion characteristics during the mode switching process with various control parameters, such as injection timing, numbers, duration, exhaust gas recirculation (EGR) rates, were detailed analyzed at medium and high engine loads. Experimental results show that the smoothness mode switching between ICCI combustion and CI combustion can be achieved within one cycle after switching another combustion mode at medium and high engine loads, and less fluctuation of IMEP is observed. At medium load, there is a wide range of butanol energy ratio (EButanol) to achieve smooth mode transition with stable combustion. However, at high engine load, higher EButanol and earlier biodiesel second direct injection timing are inadequate for the mode transition because of the higher combustion noise. EGR strategy is used to improve the smoothness of CA50 and exhibit NOx emissions. It is not needed the cycle-by-cycle injection modulation to achieve the smoothness of CA50 and the same level of NOx emissions when the EGR rate is 34.2% under ICCI combustion and 37.6% under CI combustion, respectively, with insignificant changes of IMEP and acceptable maximum pressure rise rate.

This paper investigated the mode transition between ICCI low temperature combustion and conventional CI combustion with the parameters of energy ratio, intake temperature and engine load, and the control strategies were system analyzed to improve the smoothness during the mode transition process. Results shown that the direct mode switching from ICCI combustion to CI combustion (ICCI-CI) was suitable at low engine load, but the fluctuation of IMEP was higher when direct mode transition from ICCI to CI (ICCI-CI) . Retarded the biodiesel injection timing to -38 o CA ATDC in the first transitional cycle could reduce the combustion instability. Biodiesel and butanol fuel compensation in the first cycle when the combustion mode switched to ICCI also could reduce the fluctuation of IMEP, and the corresponding fuel adjustment of biodiesel and butanol were relatively small, in which the increased fuel of biodiesel and butanol were 4.5%-11.1% and 2.6%-5.3%, respectively. The fluctuation of IMEP was higher when biodiesel compensation using two transitional cycles, that was not suitable for the smoothness of CI-ICCI mode switching process. However, the butanol compensation using two transitional cycles could enhance the combustion stability and reduce the fluctuation of IMEP during the CI-ICCI mode switching.

Thin film bulk acoustic resonator (FBAR) plays a very important role in radio frequency (RF) filters used in cell phone and other wireless systems. Although FBAR is commercialized, the design/process interactions on the frequency response variation in FBAR device are still lacking. Design and fabrication are two crucial aspects affecting FBAR device performance. In this report, various solidly mounted resonators (SMR) were designed, fabricated and analyzed to study wafer-level site-to-site RF variation on design and fabrication process. As a key process step for SMR FBAR, the optimization process of Mg-doped ZnO piezoelectric thin film deposition was studied by varying thin film sputtering conditions using various sputtering targets and by post annealing treatment after the deposition. The quality of this crucial layer was verified by XRD on its (0 0 2) crystallization and wafer-level FBAR RF characterization. FBAR devices with high quality were fabricated with an excellent resonant behavior near 2 GHz and a maximum return loss of −15 to 25 dB. Quality factor Q ranges from 400 to 800, with a coupling coefficient keff2 of 1.5–3%. Wafer-level and wafer-to-wafer variation of central frequency are within 1.8–2.1 GHz. Computer simulation verified that this frequency variation correlates to the piezoelectric film variation of 1.6–1.9 μm. Process control on this piezoelectric thin film is essential to maintaining the resonator frequency-controlled value when building duplexer RF circuits. The dependency of RF performance on FBAR size, density and orientation is not obvious, compared to that of the wafer-level FBAR device variation on fabrication process. Regarding to the Mg-doping effect in MgxZn1-xO piezoelectric film, the amount of Mg in MgxZn1-xO film during the sputtering process must be properly controlled within 30% to keep the piezoelectric quality. The average acoustic speed of the Mg-doped ZnO film is 6870 m/s with the estimated range of 5760–7980 m/s, which is better than that of pure ZnO film (6330 m/s).

Recently, the intelligent charge compression ignition (ICCI) combustion mode was proved to be very efficient for the internal combustion engine. Bioethanol is one of the most available renewable fuels at present. In order to improve the utilization efficiency of ethanol in internal combustion engine, this study tested the combustion and emission characteristics of bioethanol-diesel in ICCI mode at various bioethanol substitute ratios and injection strategies. The results demonstrated that with bioethanol substitute ratio of 64% ~ 68%, the indicated thermal efficiency of the engine reached high level (50.1%), and the engine emissions decreased to a low level with ultralow NOX (below 1 g/kwh) and particulate matter (particle number close to 1 × 106/cm3). The bioethanol double-injection strategy at 3:1 split ratio intensified the stability of the local heat release process, increasing thermal efficiency by 1.4%. Increasing bioethanol injection pressure diminished the possibility of local misfire increasing combustion efficiency. The dilemma of nucleation particle, HC, and CO emissions due to the low average temperature at the end of combustion could be solved by increasing bioethanol injection pressure.