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1. Introduction
The transportation sector accounted for 66% of the total US petroleum consumption and 26% of total US green house gas emissions in 1997 [1]. To address issues related to reliance on foreign oil, greenhouse gas emis-sions, and pollutant emissions, alterative transporta-tion fuels such as compressed natural gas (CNG) and liquefied natural gas (LNG) have been proposed. There will be immense economic and environmental benefits if even 10% of the transportation energy from petroleum can come from LNG. Natural gas consumption in the United States is expected to exceed 33 tcf/year by 2020, increasing from 22 tcf/year in 1997 [2,3].

1 引言

交通运输业占1997 [总数的1，美国的石油消费量和温室气体排放量的26%的总我们66% ]。对外国石油的依赖，以解决相关问题，温室气体的排放量，和污染物的排放，改善运输燃料，如压缩天然气（CNG）和液化天然气（LNG）已经提出了。将有巨大的经济效益和环境效益，如果从石油的运输能源甚至10%可以来自液化天然气。在美国的天然气消费量预计将超过33万亿立方英尺/年的2020，增加22万亿立方英尺/年1997 [ 2,3 ]。

Most of the vehicles using natural gas instead of diesel fuel run on compressed natural gas (CNG), which is typically stored in cylindrical steel tanks at pressures up to 3600 psi. One of the drawbacks of CNG is that only limited amount of fuel can be stored in trucks or buses, which reduce the driving range significantly.

大多数使用天然气代替柴油燃料压缩天然气（CNG）的车辆，这通常是存储在圆柱形钢储罐的压力在3600 psi。一个天然气的缺点是，只有有限数量的燃料可以被存储在卡车或公共汽车，这显着降低驱动范围。

Compared with CNG, LNG can provide vehicles with longer driving ranges per refueling. LNG takes up about1/600thofthevolumethat CNGoccupies atroom temperature and atmospheric pressure. Currently, LNG is being promoted primarily for heavy-duty vehicles such as trucks and transit buses. Another advantage is that LNG can be transported via ocean tankers. The disadvantage is that the boil off of LNG can cause excessive pressure buildup in LNG tanks, and therefore we have to find methods to reduce the pressure of the boil-off gas and to prevent venting of the boil-off natural gas in storage vessels, transportation tanks, and/or on-board tanks.

In this paper, we use the thermodynamic and heat transfer methods to analyze the pressure and tempera-ture changes in LNG tanks. The evolving of properties and composition of LNG fuel inside tanks as a function oftimeissimulated.The effect ofnumberofbusesfueled each day on the total fuel loss rate due to venting will be discussed. Some approaches to preventing fuel loss at LNG stations are also proposed. For example, the boil-off gas of LNG can be used to power an electric gen-erator or be re-liquefied to reduce the gas pressure.

2. Thermal analysis of boil-off of LNG in cryogenic tanks
A typical LNG fueling system consists of LNG storage vessels, LNG fueling pumps and LNG dis-pensers. LNG storage vessel is a vacuum insulated pressure vessel ranging in capacity from 6000 to 30,000 gal [4]. LNG storage vessel consists of a 9% nickel steel inner liner and a carbon steel outer liner, using double wall construction with super insulation under high vacuum. The maximum working pressure for these tanks is normally 250 psig or lower, with product stored at 50–120 psig. The LNG fueling pump is a single or multistage centrifugal pump submerged in the storage tank or in a separate vacuum-insulated sump allow本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。