MBtech News.

Full throttle for alternative fuels.

Show what CNG (Compressed Natural Gas) can do as a vehicle fuel - that is the motto of the "Natural gas innovation show" which TÜV Rheinland has organized for the 29th of April 2009 at the Nürburgring. At this press event MBtech, a development and consulting service provider, will also prove the potential of this alternative fuel with a technology carrier: A natural-gas powered sports car study based on the Mercedes-Benz SLK combines substantially reduced CO2 emission with sporty performance and the associated driving pleasure. With this dynamic interpretation of a natural gas engine, MBtech demonstrates its competence as a development partner for alternative drive systems - for both combustion technology and vehicle integration. The innovative individual technical solutions which MBtech has developed for the CNG demonstrator - such as the injector concept and the exhaust system - can also be transferred to other vehicle applications and can make natural gas, a low-consumption and emission-friendly fuel, even more attractive in future.

The development and consulting service provider, MBtech, proves that driving pleasure and dynamic driving can be realized alongside economy with CNG using a technology carrier based on the Mercedes-Benz SLK: "With the CNG demonstrator we have realized an uncompromisingly sporty and powerful vehicle engine with substantially reduced CO2 emission," stated Andreas Biemelt, the Team Leader for Otto Engine Combustion Process Development at MBtech Powertrain and the Head of the CNG demonstrator project. The technology carrier is the focal point at the "Natural gas innovation show" organized by TÜV Rheinland and serves as a high-performance demonstration and test vehicle for the invited media representatives. MBtech engineers explain on-site the theory and practice surrounding the technical solutions embodied by this technology carrier.

Greater engine performance with improved economy
The engineers from MBtech's powertrain solutions segment have achieved a considerable increase in performance with the four cylinder compressor engine in the series SLK model in the course of the CNG adaptation. The CNG demonstrator from MBtech possesses more than 146 kW and a maximum torque of 270 Nm, which accelerates the SLK from a standstill to 100 km/h in 7.8 seconds. It has a top speed of 244 km/h.

This was made possible by combining a number of combustion process development measures. A revolutionary 4+1 injector concept played a key role: A fifth injector is utilized to enhance the traditional four injection valves. However, this does not inject the gas selectively into the cylinders but rather into the central air intake. This enables the delivery of the quantities of gas required for the high cylinder performance even in the event of strongly fluctuating gas quality. In addition, the MBtech specialists also took over the development of additional engine electronics - thus the CNG SLK also possesses an innovative sensor/actuator unit as an application tool in addition to the gasoline control unit. In combination with the pistons specially adapted to the specific characteristics of CNG fuel and an adapted turbo charger translation, this ensures that the CNG engine not only runs smoothly in every situation but even better in fact: Nonetheless, the technology carrier possesses an impressively low level of CO2 emission: Its CO2 emission of 150 grams per kilometer (NEDC) is comparable with current compact cars. It requires only 5.6 kilograms of CNG per 100 kilometers. However, the natural gas SLK not only demonstrates fuel consumption far below that of a comparable gasoline engine in the moderate speed ranges of the NEDC consumption cycle but also at full throttle. The reason: The natural gas engine developed by MBtech omits high-consumption component protection typically utilized in gasoline engines at full throttle, consisting of additionally injected fuel which prevents components such as the catalytic converter from overheating, as a result of the combustion process designed for compact combustion. At high speeds its enormous fuel saving potential comes into full play.

As a result of the tight space requirements in a sport convertible, the engineers had to cope with a drastically reduced muffler volume. Extensive detail optimizations enabled the development of a single-pipe exhaust system which fulfills both the NVH and exhaust gas back pressures requirements.

Integration made easy
As the forward-looking engine concept only achieves optimal efficiency in a harmonized full-vehicle implementation, the engineers from the vehicle engineering segment also took over the system integration of all of the additional natural gas components such as the tanks, gas lines and pressure regulators. In order to create sufficient space in the roadster's boot for the carbon composite CNG tanks, the folding roof and the associated kinematic elements has been replaced with a fixed carbon roof. These lightweight design measures for the roof and additional tanks compensate for the otherwise typical additional weight arising from gas tanks in CNG vehicles - and not only that: The lighter roof also lowers the vehicle's center of gravity which in turn results in better driving dynamics. One of the rear skirts adapted to the new exhaust system and a CNG filling connection on the driver’s side complete the body measures.

"With the CNG demonstrator based on an Mercedes-Benz SLK we have intentionally given ourselves a challenging task," summarized Biemelt: "No one would have seriously attempted to adapting a sporty vehicle model to CNG operation with the previously available know-how. However, the solutions which MBtech has developed demonstrate that the economy of natural gas as an automotive fuel can definitely be combined with the dynamics and emotions of a sports car. This gives this form of alternative fuel new perspectives for a better market penetration."