Demands for environmental protection and energy security stimulate the innovation toward the hydrogen society, in which various forms of the primary energy with a large variety of density are effectively used to produce hydrogen and electricity. Technological subjects in the hydrogen energy system relating to production, storage, transportation, and utilization are demonstrated. Hydrogen can easily produce electricity using engine and fuel cell, inversely electricity produces hydrogen using water electrolysis. The capability of hydrogen to be made from water is also one of the great advantages. That provides the ideal recycle use of water, in which hydrogen returns to water again after supplying heat and power. On the portability for vehicles, liquid fuel such as GTL and DME may also be easily synthesized by hydrogen. In particular, hydrogen fuel exhibits desirable characteristics for the combustion in spark-ignition engines. Wide range of flammability limits enables a smooth operation at a very lean mixture with low NOx level, thus the throttle control is unnecessary even at the idling condition in hydrogen engines. Experimental results of engine performance and NOx emissions are also shown using a single-cylinder test engine for a set of parameters.
Hydrogen exists as gas at ambient condition. Gaseous hydrogen has about 1/3000 of volume energy density if it is compared to gasoline. To solve this gap is one of the most serious issues to be solved before realization of the hydrogen economy. There are three realistic ways of hydrogen storage and transportation. They are compressed hydrogen, liquefied hydrogen and hydrogen storage materials. In this review, these hydrogen storage/transportation methods are explained. However, they are not competitive because every method may be utilized in various applications appropriately.
Honda has developed a new fuel cell vehicle in order to respond to global warming and energy issues. The new vehicle, the FCX Clarity, displays enhancement in driving performance and fuel efficiency against previous FCX, and embodies a new appeal not available in a reciprocating engine vehicle. The key to the Clarity's development was the achievement of size and weight reductions and increased efficiency in the fuel cell powertrain. The FCX Clarity's fuel cell powertrain has Honda's proprietary V Flow FC stack at its core, and displays a weight power density 2 times higher and a volume power density 2.2 times higher than the powertrain of the previous FCX. In addition to increasing maximum power to 100 kW, the V Flow FC stack achieves a 50% increase in volume power density and 67% increase in weight power density against the previous FC stack. Startability at low temperatures has also increased, with the vehicle able to start at -30℃. The maximum power of the Clarity's drive motor has been increased to 100 kW. In combination with the provision of power assist using a lithium-ion battery, this has enabled the realization of a smooth, powerful and continuously extendable acceleration feel. The increased efficiency of the powertrain and superior energy management have resulted in the achievement of a 60% operating energy efficiency, and the vehicle displays a fuel economy 2.1 times higher than that of a compact gasoline vehicle, and 1.4 times higher than that of a compact hybrid vehicle.
This paper reports research outlines and safety issues from an experimental study conducted recently by Japan Automobile Research Institute on the fire safety, including existing safety measures, of hydrogen fuel cell vehicles (“HFCV”). One of the concerns about the fire safety of vehicles equipped with a compressed hydrogen cylinder is the proper presence and function of a pressure relief device (“PRD”) designed to release hydrogen gas from the cylinder at the detection of a fire. Since bursting energy in a 70-MPa high pressure compressed hydrogen cylinder can reach 2.4 - 4.2kg in TNT equivalent in case of PRD failure, every necessary step must be taken to prevent PRD malfunction. If the PRD of a 35-MPa hydrogen cylinder is activated, an upward flame of as high as 10m is generated for about 1 minute. However, this short-lived flame is not thermally sufficient for adjacent vehicles to catch fire; HFCV on fire are equivalent with CNG and gasoline vehicles on fire in terms of their thermal impact on surroundings. Furthermore, HFCV fire can be extinguished by an spraying of water while dispensing with any special fire fighting measures.
Significant reductions in NOx and particulate emissions are required in diesel engines keeping their inherent high efficiency whereas spark-ignition or gasoline engines have achieved sufficiently low emission characteristics by using precise fueling control and three way catalysts. Toward 2020 and beyond, more emphasis will be placed on improvements in fuel economy in both engines to reduce oil dependence in the transportation sector, thereby mitigating global warming. It is essential to optimize combinations of technologies related to combustion, aftertreatment and fuel properties to achieve higher efficiency. Combustion technologies include downsizing the engine with turbocharging, multiple direct injection, exhaust gas recirculation and so forth. Homogeneous charge compression ignition will also be employed at part load for both engine types. For these purposes, detailed numerical combustion and chemical kinetics modeling should be developed and utilized not only to understand fuel-air mixture formation and combustion phenomena but also to devise, design and control advanced combustion systems. Such models must carefully be validated by comparing numerical results with detailed measurements associated with these phenomena.
In recent years, electrical devices like cell phone and laptop PC have been downsized. So, there is high demand to develop smaller and lighter electrical generator than it is, and many researchers have studied ultra-micro generators. Ultra-micro gas turbine, that is one of ultra-micro generators, is expected to have the energy density of several ten times higher than lithium ion battery. But, the smaller combustor is, the stronger the effect of the wall is. Therefore, thermal quenching and radical quenching through the wall cause combustion more unstable in ultra-micro combustor. Most of researches consider thermal quenching effect, while they ignore radical quenching effect. Moreover, a combustor is too small to measure combustion condition experimentally. This paper describes the result obtained by the numerical simulation for H2-Air premixed gas combustion considering radical quenching in a simple parallel plate channel and a practical ultra-micro combustor. The numerical model has elementary reaction kinetics considering adsorption and desorption reaction on wall. The details of combustion characteristics, such as temperature, mole fractions, surface coverage, reaction rate and etc, are obtained. The effects of radical quenching are especially examined by comparing with combustor considering surface reactions and one not considering surface reactions. Through these examinations, the effects of radical and heat quenching and radical quenching mechanisms are made clear.