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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.

The growing consciousness of the need to develop environmentally friendly technologies, finding alternatives for petrol as energy source, led to a significant growth of the interest to use natural gas as fuel in urban transportation. In the beginning of the decade of 1990 Mercedes Benz AG decided to offer an urban bus powered by the CNG-engine M447hG, which should have exhaust emission levels below 50% of Euro II. It is a horizontal engine with six in-line cylinders, using stoichiometric technology (λ=1) and a three-way catalyst. With 12 l displacement, the rated power is 175 kW @ 2200 min-1, and the maximum torque 880 Nm @ 1000 min-1.