Natural Gas - an Environmentally Friendly Fuel for Urban Vehicles: the Smart Demonstrator Approach

The reduction of greenhouse gases emissions remains one of the most important challenges stakes for the next decades involving all energy consumers and especially the industrial actors, although the need to make better use of energy is not appreciated to the same extent by all industrial countries. For the automotive sector, the European car manufacturers' commitment (reduction of the average fuel consumption for new vehicles to 140 grams of CO2 produced per kilometer by 2008) appears to be a valuable contribution towards meeting the recommendations of the European Commission. A sharp CO2 emission reduction requires efforts both to reduce vehicle's fuel consumption, and to widen the use of fuel with advantageous molecular hydrogen to carbon (H/C) ratio. Alongside vehicle's optimization itself, improving engine efficiency remains the main target. Reduction of engine displacement volume (commonly named downsizing) is an efficient way to achieve this target. Due to its interesting chemical properties, Natural Gas can be used to achieve low carbon dioxide levels (H/C ratio close to 4), while at the same time maintaining high thermal efficiency through dedicated engine development. The main objective of this project is to confirm (with a dedicated demonstrator vehicle) the high efficiency of CNG fuel when used in urban conditions. The target is to achieve low CO2 emissions with a maximum level of 90 g/km on the MVEG driving cycle, while keeping pollutant emissions below EURO IV level. The first step was dedicated to CNG specific engine parts design (pistons, connecting rod, crankshaft, etc.) in order to optimize CNG configuration. During the following steps, the engine has been optimized on a test bench. Valve timing and turbocharger selection have been optimized in order to obtain the best trade-off in terms of power, consumption and pollutants. The final step has been spent to calibrate the engine, firstly on the test bench and secondly on the vehicle. This work allows coping with EURO IV emissions level with optimized catalyst light-off, transient running conditions, driveability, etc.