Thorsten Schnorbus

New challenges for combustion control in advanced diesel engines

Against the backdrop of general discussions on the reduction of CO2 emissions, diesel engines will face new challenges in the future in order to meet future emission limits worldwide while maintaining good consumption figures, good driving characteristics, and acceptable costs. One of these challenges is that the fuel characteristics of diesel often varies greatly worldwide, and sometimes even within one country. As part of this article, we will illustrate FEV’s approach for the compensation of different fuel grades during combustion. The basic influencing factors for a possible compensation of the fuel’s influences will be demonstrated and analyzed, and first results for a suitable control concept will be presented.

Weltweit unterschiedliche Kraftstoffqualitäten

Vor dem Hintergrund der allgemeinen Diskussionen zur Absenkung der CO2-Emissionen ergeben sich fur den Dieselmotor in der Zukunft neue Herausforderungen, um unter Beibehaltung des guten Verbrauchs, guter Fahrbarkeit und akzeptabler Kosten zukunftige Emissionsgrenzwerte weltweit zu erreichen. Eine dieser Herausforderungen ist die weltweit zum Teil stark variierende Kraftstoffqualitat des Diesels, teilweise sogar innerhalb eines Lands. Im Rahmen dieses Beitrags wird der Ansatz der FEV zur Kompensation unterschiedlicher Kraftstoffqualitaten auf die Verbrennung dargestellt. Es werden grundsatzliche Einflussparameter zur moglichen Kompensation der Kraftstoffeinflusse aufgezeigt und analysiert sowie erste Ergebnisse eines entsprechenden Regelkonzepts dargelegt.

Advanced Thermal Management for Modern Diesel Engines: Optimized Synergy Between Engine Hardware and Software Intelligence

Both, the continuous tightening of the exhaust emission standards and the global efforts for a significant lowering of CO2 output in public traffic display significant developments for future diesel engines. These engines will utilize not only the mandatory Diesel oxidation catalyst (DOC) and particulate trap (DPF), but also a DeNOx aftertreatment system as well — at least for heavier vehicles. The DOC as well as actually available sophisticated DeNOx aftertreatment technologies, i.e. LNT and SCR, depends on proper exhaust gas temperatures to achieve a high conversion rates. This aspect becomes continuously critical due to intensified measures for CO2 reduction, which will conclude in a drop of exhaust gas temperatures. Furthermore, this trend has to be taken into account regarding future electrification and hybridization scenarios. In order to ensure the high NOx conversion rates in the EAS intelligent temperature management strategies will be required, not only based on conventional calibration measures, but also a further upgrade of the engine hardware.Advanced split-cooling and similar thermal management technologies offer the merit to lower CO2 emissions on one hand and increase exhaust gas temperature at cold start and warm-up simultaneously on the other hand. Besides this, also variable valve train functionalities deliver a substantial potential of active thermal management. In the context of this paper various concepts for exhaust gas temperature management are investigated and compared. The final judgment will focus on the effectiveness concerning real exhaust temperature increase vs. corresponding fuel economy penalty. Further factors, like operational robustness, consequences on operational strategies and related software algorithms as well as cost are assessed. The utilized reference engine in this advanced program is represented by a refined I-4 research engine to achieve best combustion efficiency at minimal engine-out emissions. The detailed studies were performed with an injection strategy, featuring one pilot injection and one main injection event, and an active, advanced closed-loop combustion control. The engine used in this study allows fulfillment of Euro 6 and Tier 2 Bin 5 emissions standards, while offering high power densities above 80 kW/ltr.As a resume, it can be stated, that with all accomplished variations a significant increase in temperature downstream low pressure turbine can be achieved. The PI and PoI quantities define dominant parameters for emission formation under cold and warm conditions. By using an exhaust cam-phaser CO-, HC- and NOx emissions can be significantly lowered, separating VVT functions from the other investigated strategies.Copyright

New Air Control Logics for HD Diesel Engines for Most Stringent Emission Demands and Best Customer Value in Terms of Fuel Consumption and Engine Response

The upcoming worldwide legislations for emission reduction demand a significant further reduction of Diesel engine tailpipe emissions for all various applications. Also the introduction of new test procedures for On-Road (WHTC – World Harmonized Transient Cycle) as well as Off-Road (NRTC – Non Road Transient Cycle) increases the challenge for compliance due to higher dynamic or transient requirements. As function of the anticipated vehicle installation and the exact legal boundaries a further strong decrease of engine-out emissions is necessary, despite the widespread use of efficient exhaust aftertreatment systems. The parallel minimization of PM and NOx engine-out emissions requests for the majority of engines significant technology upgrade in terms of FIE (Fuel Injection Equipment), EGR (Exhaust Gas Recirculation), turbocharger systems and coolers. All improvements result in a significantly lowered level of steady-state emissions over the engine map. The application of all these highly efficient technologies will result in a very complex design if a significant emission improvement on one side and robust comfortable and spontaneous engine response under all real world operating conditions on the other side have to be attained. All control functions must remain transparent to the vehicle operator, e.g. the transition between different operating modes for various purposes (normal mode, heating mode, regeneration mode, etc.). This paper provides details about the most important characteristics and results of advanced control logic for the next generation of Diesel engine applications. As an evolutionary step, the so-called ‘emission index controller’ will be described. This emission index controller provides advanced capabilities to decrease transient engine-out emissions. Also scattering and long term durability effects can be covered with such an advanced algorithm. In a second step, detailed application results from actual developments with this controller strategy will be shown in conjunction with an outlook for further developments.Copyright

Real-time capable simulation of diesel combustion processes for HiL applications:

The complexity of the development processes for advanced diesel engines has significantly increased during the last decades. A further increase is to be expected, due to more restrictive emission legislations and new certification cycles. This trend leads to a higher time exposure at engine test benches, thus resulting in higher costs. To counter this problem, virtual engine development strategies are being increasingly used. To calibrate the complete powertrain and various driving situations, model in the loop and hardware in the loop concepts have become more important. The main effort in this context is the development of very accurate but also real-time capable engine models. Besides the correct modeling of ambient condition and driver behavior, the simulation of the combustion process is a major objective. The main challenge of modeling a diesel combustion process is the description of mixture formation, self-ignition and combustion as precisely as possible. For this purpose, this article introduces a novel combustion simulation approach that is capable of predicting various combustion properties of a diesel process. This includes the calculation of crank angle resolved combustion traces, such as heat release and other thermodynamic in-cylinder states. Furthermore, various combustion characteristics, such as combustion phasing, maximum gradients and engine-out temperature, are available as simulation output. All calculations are based on a physical zero-dimensional heat release model. The resulting reduction of the calibration effort and the improved model robustness are the major benefits in comparison to conventional data-driven combustion models. The calibration parameters directly refer to geometric and thermodynamic properties of a given engine configuration. Main input variables to the model are the fuel injection profile and air path–related states such as exhaust gas recirculation rate and boost pressure. Thus, multiple injection event strategies or novel air path control structures for future engine control concepts can be analyzed.