A homogeneous mixture of natural gas with an ignition additive of DME was used to a compression ignition engine. Experimental and analytic studies on the combustion, the engine performance and the exhaust characteristics were conducted for investigating the effects of equivalent ratio and intake air temperature. Results show that the engine can run over a wide range of load with low NOx emissions and the combustion can be controlled effectively by changing the proportions of natural gas and DME.
The hydrocarbon composition in the exhaust of a dimethyl ether (DME) fueled CI engine and sensitivity correction techniques for a THC analyzer were discussed. The formation process of unburned hydrocarbon species was also investigated by in-cylinder gas sampling. The results showed that since HC emissions in the exhaust consist of DME and a small amount of lower hydrocarbons, a constant correction factor could be applied for THC analyzer, within an error of ±5%. The gas sampling results indicated that high levels of C2 components, such as C2H2, C2H4, C2H6 were formed during combustion process, and were mostly oxidized before the exhaust valve opened.
<div class="section abstract"><div class="htmlview paragraph">In transportation sector, higher engine thermal efficiency is currently required to solve the energy crisis and environmental problems. In spark ignition (SI) engine, lean-burn strategy is the promising approach to improve thermal efficiency and lower emissions. Olefins are the attractive component for gasoline additives, because they are more reactive and have advantage in lean limit extension. However, owing to lower research octane number (RON), it is expected to exhibit the drawback to reducing the anti-knock performance. The experiments were performed using a single-cylinder engine for 6 fuel types including gasoline blends which have difference in RON varying between 90.4 and 100.2. The results showed that adding olefin content to the premium gasoline provided unfavorable effect on auto-ignition as the auto-ignition happened at unburned gas temperature of 808 K which was 52 K lower at excess air of 2.0. Thus, it reduced anti-knock performance. Additional oxygenated fuels such as ethanol and ETBE helped improve the anti-knock performance by 4.9% and 5.7% respectively. S5H+1-hexene fuel was found to be highest reactivity which would have high possibility of knocking. HCHO emission increased linearly with decreasing RON at lean burn condition which was expected to undergo low-temperature reaction processes.</div></div>
Surface materials on airless solar system bodies exposed to interplanetary are gradually changed their visible to near-infrared reflectance spectra by the process called space weathering, which makes the spectra darker and redder. Hapke et al. proposed a model of weathering: vapor deposition of nanophase reduced iron (npFe(sup 0)) on the surfaces of the grains within the very surface of lunar regolith. This model has been proved by detailed observation of the surfaces of the lunar soil grains by transmission electron microscope (TEM). They demonstrated that npFe(sup 0) was formed by a combination of vapor deposition and irradiation effects. In other words, both micrometeorite impacts and irradiation by solar wind and galactic cosmic ray play roles on the weathering on the Moon. Because there is a continuum of reflectance spectra from those of Q-type asteroids (almost the same as those of ordinary chondrites) to those of S-type asteroids, it is strongly suggested that reflectance spectra of asteroids composed of ordinary chondrite-like materials were modified over time to those of S-type asteroids due to weathering. It is predicted that a small amount of npFe(sup 0) on the surface of grains in the asteroidal regolith composed of ordinary chondrite-like materials is the main agent of asteroidal weathering.
In recent years the revolution in aberration correction technology has made ultrahigh resolution imaging and analysis routinely accessible on transmission electron microscope (TEM) and scanning transmission electron microscope (STEM).Particularly for catalyst or fuel cells, many scientists would like to observe the behavior and understand the degradation process in real environment (in-situ) with TEM.We have reported a evaluation of environmental TEM and STEM imaging with a newly developed analytical 200 kV cold field emission (CFE) TEM equipped with a probe-forming aberration corrector, the model is Hitachi HF5000 (Figure 1(a)) [1][2].The base microscope is capable of TEM, STEM imaging with bright field (BF), annular dark field (DF) detectors, and secondary electron (SE) imaging.The probe-forming aberration corrector with automated correction of up to third order aberrations allows users to obtain aberration-free STEM illumination optics with minimized effort.In addition, the stability for the newly designed high tension circuit is less than 1 ppm which is critical to realize high energy resolution for analytical work using CFE gun and high spatial resolution for imaging.This microscope is featured high-resolution imaging with higher specimen tilt angle and sensitive X-ray analysis with dual SDD (silicon drift detector) assignment and capable of chemical analysis with a post column electron energy-loss spectrometer (EELS).For in-situ operation, we have modified a standard vacuum system suitable for high gas pressure configuration with differential pumping apertures (orifices) and additional turbomolecular pump (TMP) to improve the evacuation capability in order to keep the gun pressure low enough to operate CFE (Figure 1(b)) [3].This microscope enables to record three scanning image signal simultaneously SE, BF and DF-STEM in fast scan rate.Figure 2 shows simultaneously recorded STEM images of gold nano-particles on carbon thin film.The simultaneous observation ideally helps to reveal the processes by the surface morphology as well as motion inside of catalyst, and even SE allows atomic resolution imaging [4].In the preliminary study, a specimen heating holder was used and increased a temperature of 200 degrees C. We employed an air as a reaction gas was induced by the gas injection nozzle that is attached on the holder.Another independent gas injection nozzle can be installed at the specimen chamber port, which permits to operate many kinds of holders.Figure 3 shows a sequence of in-situ SE images recorded at 200kV to show Pt particles on the carbon surface movement and migration at a temperature of 200 degrees C under a pressure of 5.5x10 -3 Pa.The vacuum pressure is measured at the main vacuum pipe.While increasing the specimen temperature we observed coalescence of some particles.Then under the air injection, some Pt particles on surface were buried in the carbon support which suggests the degradation process of the catalyst [3].
The penetration of DME spray is shorter than that of diesel fuel when the same injection system is used because DME cannot be injected at high pressure like diesel fuel due to its high compressibility. Chris reported that supercritical gasoline spray has a wider spray angle and has increased penetration. Therefore, there is possibility that supercritical DME spray has increased penetration. However, there is no observation on the shape, development process, combustion of supercritical DME spray. In this study, the spray and combustion characteristics of supercritical DME in an optically accessible constant volume vessel were observed under turbo charged engine-like ambient condition. Parallel light shadow graph and diffused light shadow graph method were applied to image the liquid and vapor phase behavior. Moreover, the spray angle of supercritical spray was compared with that of subcritical one under the same ambient condition to confirm the influence of fuel temperature. The results show that there is no significant difference in spray shape between supercritical and subcritical spray under turbo charged engine-like ambient condition. Moreover, the spray angle of supercritical spray was bigger than that of subcritical one under relatively low pressure ambient conditions. These can be explained by p - v diagram. The reasons are as follows the difference in specific volume between liquid and vapor is small at ambient pressure near critical pressure. The ignition timing of the supercritical spray was slightly earlier than the subcritical spray.
To improve the water transport of a gas diffusion layers (GDL) in a polymer electrolyte fuel cell (PEFC), the effect on the wettability distribution in the thickness direction of the GDL was investigated by a lattice Boltzmann method (LBM). Because much water is generally accumulated in the GDL under rib, the water behavior in the GDL under rib was the focus. The result showed the water in the GDL was significantly reduced by the wettability distribution in the thickness direction made by weak and strong hydrophobicity because the water in the lower of GDL was pulled up to the upper of GDL and the water in the upper of GDL was transported into the channel along the weak hydrophobic region. The depth of the weak hydrophobic region from the GDL surface equivalent to about four pores advantageous to reduce the water in the GDL.
