Jost Weber

Potential of Dimethylether as an alternative Diesel fuel for a CO 2 sustainable powertrain solution

Worldwide, combustion engines will remain as major power unit for vehicle propulsion in long-term. Consequently, immediate measures are claimed to reduce the current CO2 production from combustion engines which are accomplished by three approaches: (1) an increase of the thermal efficiency, (2) the application of fuels with low carbon content and (3) the production of fuels from renewable feedstocks. The first aspect clearly emphasizes compression ignition (CI) engines, the second aspect draws the attention to hydrogen and single C-bonded fuels and the third aspect has initiated sensitive discussions about renewable resources which lead to the commitments of first/ second/ third generation biofuels. In this context, the use of Ethers as neat or blended fuels for combustion engines has been discussed for more than 20 years. Among these, the simplest compound, Dimethylether CH3-O-CH3 (DME), has an exceptional position as a neat fuel for compression ignition (CI) engines due to its excellent ignition and combustion properties which have been well investigated published by many authors.

Reduction of Diesel Engine Emissions Performance – Further Steps Towards a Fast and Flexible Fuel Injection

Diesel engines remain the main powertrain concept in view of efficiency and robustness. On the one hand the emissions towards the future EU CO2 limit of 95 g/km by 2021 further demands the reduction of the fuel consumption. On the other hand the new WLTP test cycle and RDE emissions tests demand to reduce the engine-out raw emissions. So far, the main development path of the fuel injection system is focusing on increasing the rail pressure. The increase of the no. of injection events is another approach that aims for phasing the combustion in the working process of the Diesel engine efficiently. This approach is limited by the needle opening speed and capability of closed-coupled injection events. Such features were so far restricted to Piezo injectors. Recently the solenoid injector was enhanced to close this gap and it was firstly tested on an hydraulic test bench and a 4 cyl. passenger car Diesel engine. The hydraulic and engine performance is compared against the solenoid injector G4S and the Piezo injector G4P. With increasing the injection rate steepness and reducing the hydraulic intervals, a triple pilot injection strategy is applied to control the ignition delay and rate of combustion. The steep injection rate reduces the soot emissions without compromising the combustion noise. On the other hand the short interval and fast needle actuation reduces the injection and combustion duration. Thanks to this improved hydraulic performance the BSFC could be improved by 1.7% and soot emissions reduced by 36% at engine part load conditions (2000 rpm, BMEP=6 bar).

An Investigation of Flow in Nozzle Hole of Dimethyl Ether

For over twenty years, DME has shown itself to be a most promising fuel for diesel combustion. DME is produced by simple synthesis of such common sources as coal, natural gas, biomass, and waste feedstock. DME is a flammable, thermally-stable liquid similar to liquefied petroleum gas (LPG) and can be handled like LPG. However, the physical properties of DME such as its low viscosity, lubricity and bulk modulus have negative effects for the fuel injection system, which have both limited the achievable injection pressures to about 500 bar and DMEs introduction into the market. To overcome some of these effects, a common rail fuel injection system was adapted to operate with DME and produce injection pressures of up to 1000 bar. To understand the effect of the high injection pressure, tests were carried out using 2D optically accessed nozzles. This allowed the impact of the high vapour pressure of DME on the onset of cavitation in the nozzle hole to be assessed and improve the flow characteristics.