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With the discovery of oil and gas in the pre-salt Santos and Campos basin, the supply of natural gas (NG) is expected to increase considerably, so the use of compressed natural gas (CNG) in city buses will be an important option for reducing the overall consumption of fossil diesel fuel and a reduction in operating costs in São Paulo and Rio de Janeiro Metropolitan Areas in Brazil. A vehicle with an engine that can run on pure diesel or diesel and CNG has advantage over a vehicle that works exclusively with CNG, because when there is no availability or the lack of CNG, the vehicle / engine operates with diesel only. Another benefit of this technology is the resale value in Brazil, because after the life cycle of use in theses two big cities, Urban Buses are sold country side to small cities where CNG is not available.

In order to use waste (BIOMASS), such as rice rind, we use a gasification process, which is a form of increasing the energetic use of Biomass. A fluidized bed gasifier at UNICAMP was used with an engine of 5.965 liters of total displacement and 6 cylinders, with compression ratio of 12:1 in the OTTO cycle and which is originally used in vehicles driven by compressed natural gas, to work with low heating power gas (4 to 6 MJ/Nm3) produced by the gasifier. The following values were obtained in the tests: Power ( kW) = 40.7 @ 1800 rpm, Feed (crankshaft degrees) = 30 Exhaust temperature (°C) = 596 Lambda = 1,12 Maximum Combustion Pressure (KPa) = 4000

The development of the natural gas engines Mercedes-Benz has been constantly improved and used in buses in Germany, Australia, and other countries and also in São Paulo City (Brazil). With the purpose to enlarge of the natural gas engine using, DaimlerChrysler do Brasil developed the first extra heavy-duty truck moved by natural gas of Brazil with the engine M447LAG. The vehicle was applied to draw a moving stage called trio elétrico for the carnival 2001 in Salvador City. The electric power to supply the sound and illumination of the moving stage was produced by generating group moved with 2 natural gas engines M366LAG Mercedes-Benz.

The combustion development of the Mercedes-Benz MY1999 CNG-Engine M366LAG is discussed.With a dis-placement of 5.958 l and 6 in-line cylinders, this engine has a rated power of 170 kW @ 2600 min-1, and a maximum torque of 720 Nm @ 1560 min-1. It can operate using CNG of considerably lower methane number [3] than the previous version, while improving performance, fuel consumption and emission values. Major modifications were performed to achieve these results. Mixture motion and combustion were improved using a high-swirl intake port. The new engine management system provides fuel injection, full airflow control and closed-loop lean burn operation. Due to its higher tolerance to gas quality fluctuations, the new M366LAG can be offered to a wider range of customers than the previous versions, without the risk of engine damage or operational problems.

A computational fluid dynamics (CFD) analysis of the M366LAG in-cylinder flow was performed to explain what are the reasons for the measured engine slower combustion which results from the replacement of the intake valve seat angle of 45° by 20°. Simulations showed that a quite different in-cylinder flow resulted from the different designs. The 20° geometry was found to generate a weaker turbulent field at the end of the compression stroke, specially around spark plug, which was identified as the cause of the slower combustion. The weaker turbulence is a result of a less coherent flow structure which is less capable of both storing the main flow kinetic energy until the compression stroke end and of taking advantage of squish to generate turbulence.

The heavy-duty natural gas engine has been subject of growing interest as a feasible alternative for the reduction of pollution levels in urban centers, where currently diesel vehicles predominate. This paper summarizes the development of the Mercedes Benz compressed natural gas engine M366LAG, which reached competitive characteristics of Diesel engines, like fuel consumption, weight / power ratio and thermal loading, by matching the turbocharging technology with charge cooler and the concept of lean burn combustion. An oxidation catalyst was developed and emissions less than 50% of the EURO II limits were achieved. With 5,958 1 of displacement and 6 cylinders in line, the M366LAG provides a power of 170 kW @ 2600 min-1 and 720 Nm @ 1560 min-1 as maximum torque.