The objective of current research on internal combustion engines is to further reduce exhaust emissions while simultaneously reducing fuel consumption. The resulting measures often mean an increase in complexity of internal combustion engines, which on one hand increases production cost and on the other hand increases the susceptibility of the overall system to defects. It is therefore necessary to develop technologies which can generate an advantage for the consumer despite increasing complexity. Within the scope of the project “High Efficiency Diesel Engine Concept” (“Hocheffizientes Diesel-Motoren-Konzept” HDMK), funded by the Federal Ministry of Economic Affairs and Energy with TÜV Rheinland as project management organization (funding code: 19U15003A), two engine concepts were investigated and combined on a John Deere four-cylinder inline engine.
On the one hand, a new cylinder activation concept (“3/4-cylinder concept”) was implemented with the aim of reducing fuel consumption. On the other hand, a fully variable valve train was developed for this engine, which both improves the functionality of the 3/4-cylinder concept and can have a positive influence on exhaust emissions through internal exhaust gas recirculation.
A comparison of this engine concept with its series reference based on measurement data showed a fuel economy advantage of up to 5.2% in the low load field cycles of the DLG PowerMix. The maximum fuel consumption benefit in the low load engine regime exceeded 15% in some of the operating points.
As a final step, the engine was modified for the integration into an existing and working tractor, maintaining the available installation space of the powertrain.
A complex task regarding the control of the homogeneous charge compression ignition (HCCI) combustion process is the control of combustion timing, represented by the crank angle at which 50 per cent of the fuel mass inside the cylinder is burned (MFB50). The most important parameters for transient MFB50 control are the mass of (hot) residual gas inside the cylinder (e.g. retained by internal exhaust gas recirculation), the injection strategy (in the case of direct fuel injection), and the spark timing. In this paper, the potential of a corona ignition system is examined in comparison with a conventional spark ignition system for the HCCI combustion process. For this purpose, thermodynamic investigations have been carried out on a single-cylinder research engine, combined with one-dimensional gas exchange analyses and high-speed visualization of combustion in a transparent engine. It could be demonstrated that both ignition systems are capable of influencing the autoignition process. The corona ignition system, however, allows a much later ignition point for achieving the same MFB50. This is due to the spatial character of the initial ignition area of corona ignition. In addition, the corona ignition system is more robust with respect to a change in the boundary conditions, such as a variation in the residual gas rate or the mixture composition. It is therefore more reliable in initiating autoignition, even in critical operating conditions. Additionally, it was found that the corona ignition system permits the combustion to be influenced by means of a variation in the ignition energy, which appeared to be not the case for the conventional ignition system.
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