Proceedings of the
Second International Energy 2030 Conference,
November 4-5, 2008, Abu Dhabi, U.A.E.
Comparison of Engine Performance and Pollutant Emissions from Gasoline vs. Natural Gas Driven Vehicles
Mohamed Sassi
The Petroleum Institute, UAE
Sai Fok
The Petroleum Institute, UAE
Isoroku Kuobo
The Petroleum Institute, UAE
Abstract
Transportation is a major contributor to air pollution. After World War II, people became aware that
the exhaust emissions from vehicles can be a major cause for the increasing air pollution in congested
cities. The exhaust emissions from diesel and gasoline vehicles mainly contain unburned hydrocarbons
(HC), carbon monoxide (CO), Carbon dioxide (CO2), oxides of nitrogen (NOx), and a large amount of
particulate matters. These gases are the main causes of the greenhouse effect and acid rain. Many
illnesses had been reportedly found to be related to these pollutants.
The deterioration of the air quality and the effect of global warming had encouraged many researchers to
search for “cleaner” alternative fuels. The results of many of these researches had indicated that natural gas is
a “cleaner” fuel for vehicles compared with the gasoline or diesel. Natural gas is a form of petroleum
produced by chemical reactions of the buried remains of organic material from earlier ages. The main
constituents are a mixture of propane, butane, and methane. It is colorless, odorless and non toxic. Table 1
summarizes a general comparison of pollutant emissions from natural gas, gasoline and diesel vehicles. In
general, natural gas vehicle can reduce NOx emissions by about 80% compared to gasoline and diesel
vehicles. The exact emission reduction will depend on the vehicle, its state and the operating conditions.
Although natural gas is considered to be an environmental friendly fuel and has been used in some
vehicles in many countries for quite some time, the commercial application of natural gas for
transportation purposes is still not wide-spread. The reasons for this lack of popularity can be attributed to
many factors. First, the global network for the logistic distribution of conventional fuel such as gasoline
and diesel has been well established. On the other hand, there are very few refueling stations for natural
gas vehicles in many countries. The lack of refueling facilities has hindered the utilization of natural gas in
vehicles. Second, dominant vehicle manufacturers have been looking into the issue of alternative fueled
vehicle but their current focus is still on the mass production of conventional fueled models. As a result, the
evolution of natural gas vehicles is heavily dependent on retrofitting kits [1]. The lack of readily available
off-the-show room models of natural gas automobiles has limited the consumer interests in this fossil fuel.
Although these two historical factors had hindered the demand for natural gas, there are strong indications
that this will change in the near future. In recent years there is a growing concern on the increasing price of
crude oil. This economical factor, together with the worsening environmental issues due to global warming
and the increasing health problems associated with air pollution, has resulted in the growing importance of
natural gas as an emerging energy resource. Economically, the natural gas market is also more stable than the
oil market. The current price of natural gas is about half the price of crude oil. The reason for this economic
stability is that the estimated world reservoirs for natural gas are much bigger than for oil.
The UAE government is well aware of the growing global importance of natural gas and the potential
benefits in terms of environmental issues. In 2005, the UAE president had directed the Abu Dhabi
National Oil Company to execute the natural gas vehicle project due to its importance in providing a safe
and clean environment. It is targeted that natural gas would account for 20% of Abu Dhabi total fuel consumption by 2012.
To realize this plan, the government in Abu Dhabi had prepared a strategy with the
help of the concerned establishments, which include the environmental agency, the Federal Environmental
Agency (FEA), ADNOC (Abu Dhabi National Oil Company), Abu Dhabi police, etc. One of the initial
tasks in this strategy involved the changeover of Abu Dhabi entire taxis fleet to natural gas and to refurbish
