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The use of CNG in light-duty vehicles is well known and widespread in Brazil, mainly in the state of Rio de Janeiro. In theory, the application of this technology could provide greater energy efficiency and lower emissions of pollutants. However, it is known that the majority of CNG kits installed do not meet the environmental requirements established by the Brazilian legislation. This work quantifies the average emissions from light-duty vehicles converted to CNG use in the Metropolitan Area of Rio de Janeiro, where 47% of the Brazilian CNG fleet runs. For this purpose, initially a field survey of gas stations was performed in this Region, in order to define the representativeness of CNG kits in terms of technology generation and brand, as well as manufacturer, model, displacement, original fuel and manufacture year of vehicles in which such kits were installed.

Rapid Compression Machine (RCM) is an experimental tool developed to study combustion parameters. It allows to measure cylinder pressure and piston displacement as well as to film combustion through a transparent piston head. RCM is pneumatically and hydraulically driven device and it reproduces a single combustion shot, considering a compression and a partial expansion stroke. The RCM used in this work was originally manufactured for investigate the diesel engine combustion. This paper describes the RCM adaptations made in order to investigate the dual-fuel combustion characteristics of lean natural gas-air mixtures, using diesel fuel as ignition source. The RCM was equipped with high pressure common-rail diesel injection system and a compressed natural gas system. The natural gas and air were introduced in the combustion chamber, prior to compression stroke, and the pilot diesel fuel was adjusted to typical injection timing and durations of Diesel engines.

Over the last few years, a growth of the Brazilian light duty vehicle fleet converted to Natural Gas (NG) has been observed. This is mainly due to license tax reductions on NG vehicles; the increase of the NG distribution around the country and attractive price difference between NG and other fuels. The Brazilian CNG (Compressed Natural Gas) light-duty vehicle fleet has currently reached more than 1,4 million units, being the 2nd largest in the World. ANP (Brazilian National Petroleum Agency) published in 2002 Resolution no104, which defines the NG specification for automotive application. The IBAMA (Brazilian Institute for Environment and Natural Renewable Resources) published in 2002 Resolution no 291, which defines ways for the environmental certification of the NG conversion kits.

Brazil is known for its long experience on using alternative fuels, mainly ethanol for light duty vehicles. In 2002, it was released the Flexible fuel car that can run with gasohol (gasoline with 22% of ethanol), hydrated ethanol or any blend of these fuels. By the end of 2006, national production of these vehicles represented around 80% of the total. Brazil is also the second world fleet of Natural Gas Vehicles (NGV), with more than 1,4 million light duty converted vehicles. This paper describes the development of a computational thermodynamic model of compression, combustion and expansion processes of gasohol, ethanol and Natural Gas (NG) for the cylinder pressure curve prediction of a Flexible Fuel engine, working with a NG kit installed. The combustion process is modeled using a Wiebe function, which establishes the mass fraction of burned fuel. Convective heat transfer to cylinder walls is estimated with an empirical correlation for heat transfer coefficient determination.

This paper describes the development of a computational thermodynamic model of compression, combustion and expansion processes of gasohol, ethanol and Natural Gas (NG) for the cylinder pressure curve prediction of a Flexible Fuel engine, working with a NG kit installed. The combustion process is modeled using a Wiebe function. Equations for specific heat at constant pressure (Cp) were developed for each fuel for temperatures up to 4000 K. The model output generates the cylinder gas pressure and temperature, work output and heat release profiles as functions of crank angle, allowing studies of engine performance parameters in different working conditions for each fuel. The differences between the experimental and simulation results were lower than 4% for the maximum cylinder pressure value.