Sebastian Walter Freund

Sensitivity analysis of adiabatic compressed air energy storage

The increasing use of fluctuating renewable energy represents a challenge for the German electricity market. Electricity storage plants can provide flexibility to the energy system and the development of new, efficient and economical energy storage technologies is of great importance. In this paper, the use of compressed air energy storage plants in the German electricity market is simulated and a sensitivity analysis is carried out. The optimization of the system is done to minimize at each time step the total system costs. The analysis shows the influence of storage plant parameters such as efficiency, storage capacity and natural gas usage on the dispatch and operation hours. It is performed over one year and for three different future scenarios. The results indicate that utilization of storage plants will increase in each scenario considered from 2025 to 2035 but remains in most cases significantly below the maximum capacity of 3000 h/a power generation. While the operation of storage plants lowers the total electricity cost, earnings per plant and profits are not necessarily positive: the wholesale price signals do not create enough revenues to justify the investment in CAES plants.

Comparison of Alternative EGR Systems for a Medium Speed Diesel Engine

Meeting future regulations for diesel engine NOx emissions with in-cylinder solutions will require a high rate of exhaust gas recirculation (EGR). For medium speed diesel engines, the exhaust manifold pressure is typically lower than that of the intake manifold, necessitating a rise in the exhaust gas pressure for exhaust flow to be introduced into the intake manifold. In this study, four high-pressure EGR engine concepts are investigated as a means to meet EPA Tier 4 NOx emissions. These concepts include a system with an EGR pump, one with a power turbine downstream of the turbocharger (i.e., turbocompounding), one with dedicated donor EGR cylinders and the use of a backpressure valve. For each system, an optimum set of parameters that included intake valve timing, intake manifold pressure, and fuel injection timing were found that satisfy the emissions requirements while staying within the mechanical limits of the system. From an efficiency perspective, the turbocompound system is generally superior, followed by the donor cylinder concept. The EGR pumping system typically has lower overall efficiency due to the compressor power requirement and the use of a backpressure valve, representing the baseline for comparison, produced the lowest system efficiency.Copyright