Fino Scholl

Development and Analysis of a Controlled Hot Surface Ignition System for Lean Burn Gas Engines

Spark ignition constitutes the most common way of mixture inflammation for gas engines of CHP units (combined heat and power). However, spark plug durability is limited due to spark erosion. High maintenance costs as a result of frequent spark plug replacements are the consequence. Beside the durability aspect, the inflammation of lean mixtures makes high demands on the inflammation process itself. Due to the small reactive mixture volume, the level of air-fuel ratio as well as the efficiency increase is limited. The ignition by means of a hot surface enables an increase of the reactive mixture volume and, as a result, an enhancement of the lean burn limit.A hot surface ignition (HSI) system was developed for stationary lean burn operation in due consideration of low manufacturing costs and electrical characteristics that allow a reliable control of the ignition timing. The main component of the inflammation element is a pin-shaped glow plug, whose temperature can be regulated by adjusting the electrical power. Due to external influences such as fluctuating ambient pressure and gas quality a control unit is essential for securing an optimal combustion phasing of the engine.Several designs of hot surface ignition, including passive prechamber and shielded versions, were tested on a single cylinder test bed engine operating with a homogeneous air-petrol mixture. The engine tests were accompanied by 3D flow simulations. The trials showed that the power consumption, and hence the temperature of the hot surface, as well as the flow conditions around the glow plug have a strong influence on the ignition timing. Furthermore, a strong correlation between the mean combustion chamber temperature and combustion phasing became evident. Based on this coherence, it was possible to develop a closed-loop control that adjusts the combustion phasing by controlling the combustion chamber temperature at a stationary operating point.The shielded inflammation element stood out to be the target-aiming version of hot surface ignition. It is characterised by an accelerated inflammation which allows reducing the cycle-to-cycle variations compared to prechamber spark ignition and, hence, to enhance the lean burn limit. As a result, a significant improvement of the efficiency-NOx trade-off is possible.The obtained results provide the basis for further trials on a gas engine CHP module operating with natural gas.Copyright

Numerische und experimentelle Untersuchungen zu Miller- und Atkinson-Steuerzeiten bei konstantem effektivem Verdichtungsverhältnis am Beispiel eines stationär betriebenen gemischansaugenden Gasmotors

Die zukunftige Verscharfung der Emissionsgesetzgebung fur erdgasbetriebene Blockheizkraftwerke verlangt nach neuen Ansatzen in der Brennverfahrensentwicklung. Im kleineren Leistungsbereich werden derzeit hohe Wirkungsgrade und niedrige NOx-Emissionen durch homogen magerbetriebene Erdgasmotoren erreicht. Zwar konnen zukunftige NOx-Grenzwerte mit Erhohung der Ladungsverdunnung eingehalten werden, jedoch stehen dieser Masnahme Wirkungsgradeinbusen aufgrund einer verschleppten Verbren-nung gegenuber.

Effect of intake manifold water injection on a natural gas spark ignition engine: an experimental study

Design and development of gas CHP (combined heat and power) engines are strongly influenced by the progressively more severe European NOx emissions normative. Water injection represents a promising approach to reduce these emissions while attaining high engine efficiency. In this work, the effect of intake manifold water injection on combustion parameters and performance of a single-cylinder naturally aspirated natural gas spark ignition engine is presented. First, the most appropriate injector was selected, using a spray test bed. Subsequently, engine experiments at constant indicated mean effective pressure (IMEP) and engine speed were conducted with water-fuel ratios of 0.1 to 0.3. IMEP was kept constant at about 6.3 bar by adjusting both air-fuel ratio and spark timing. A NOx reduction of 0.2 g/kWhi (15 %) for a constant ISFC of about 204 g/kWhi was achieved. In the low NOx regime, water injection allows for an improvement of the NOx-ISFC trade-off, while leading to poor fuel consumption at same NOx in the high efficiency regime. Furthermore, water injection implies a reduction of intake mixture temperature, lengthened burning delay and combustion duration and a moderate increase of combustion instability.