Heavy duty diesel whole space combustion

An optical engine has been designed and installed at Chalmers. The optical engine is a one-cylinder research version of a Volvo 4-valve diesel engine based on an AVL 501. The optical access is provided by two fused silica windows in the upper part of the cylinder liner giving the horizontal access trough the cylinder. The vertical access is given by one of the exhaust valves replaced with a fused silica window. Further is the cylinder head prepared with endoscope entrances. The engine has also an EGR system, which is integrated with the rest of the engine control system. The optical engine is used for laser diagnostics. Different optical methods are applied in order generate measurements data. The data is used for validation of CFD codes. The engine will be further used in other EU projects, for example GREEN.

Based on single cylinder engine tests, the findings were applied to a multi-cylinder diesel engine with 7,8 dm3 cylinder capacity. For these tests, the engine was converted from a unit injector to a common rail injector system and a system allowing very high exhaust gas recirculation (EGR)rates was developed. With this diesel engine for commercial vehicles higher BMEP's (up to 10 bar) could be realised. Above this value both the fuel consumption and the emissions deteriorated. Therefore, an application of this combustion system is only feasible in a dual mode form; i.e. at low load homogeneous combustion and above up to full load with a conventional heterogeneous combustion. In this case still exhaust gas aftertreatment is needed, resulting in a substantial increase in engine cost. This possibility was investigated for truck and bus applications. In a truck application the fuel consumption is higher than with a conventional system and only a small reduction in AdBlue-consumption was noted.

The HD application of HCCI combustion mode based on the dual mode NADI(TM) concept lead to the following conclusions when applied on a single-cylinder engine: -With multiple injection strategies, HCCI running is possible up to 15 bar at mid-speed with quasi zero NOx emissions, soot slightly higher to series engine and limited impact on BSFC (LP loop not taken into account) -Limited CO and HC emissions which are compatible with conventional aftertreatment -Extended HCCI range is possible with increased injection pressure and decreased compression ratio (problem with cold start and impact on BSFC) - Performance at full load is comparable with the series engine - CRT technology is efficient to treat CO and HC emission in HCCI and particulate emission at full load The transfer of the technology to multi-cylinder engines is limited by the turbocharger performances, which does not allow the high EGR rate required for an efficient control of combustion. At low load (BMEP 5to 8 bar) HCCI running even with single injection, simultaneously proves very low NOx and soot emissions albeit with an impact on BSFC (air loop). Higher BMEP generates considerable impact on fuel consumption and is limited.

These results will be used to improve internal knowledge on the subject. The existing spray model will be refined and a tool for engine combustion bowl design will be developed. Delphi Research and development will use the results but also OEM's and universities collaborating on the HCCI projects. The benefit will be the improvement of existing technique to study HCCI and a better understanding of early injection and narrow cone angle sprays.

3-D simulations for HCCI mode were performed to support the development and optimisation of HD HCCI concepts. The code used for this simulations corresponds to the IFP state of the art for HCCI combustion. The simulations allow the selection of best combustion chamber geometries and adapted spray nozzles. Influence of injection strategies is evaluated for their influence on performance and pollutant emissions. NOx and particulate level and trends are in good accordance with engine results demonstrating the reliability of the models for HCCI combustion.

These results help to solve the design and process challenges of HCCI type FIS. The results will be relevant to design and manufacturing areas but also OEM's which are our customers. The general public will benefit from future engine using these types of innovative FIS. HCCI needs a tailored fuel injection system. Requirements in terms of maximum injected flow per unit time, maximum pressure, nozzle configuration (number of holes, sizes holes) and spray pattern are specific to the HCCI combustion concept studied. Delphi has identified the relevant fuel injection system requirement and corresponding designs to promote and control the HCCI in a HD diesel engine. The main innovative feature is a nozzle design that allows us to give the required narrow cone angle spray pattern with good flow characteristics and the required durability. Benefits from this results will be seen through reduction of engine emissions.During the course of the project the relationship between Valve in flow and V out flow (both measured after honing) was further explored and was extended to include nozzles with narrow cone angles. Experimental nozzles were made with up to 24 injection holes. Injection pressures up to 2000 bar were explored.

Risultati finali

Condividi questa pagina

Scarica