Reducing fuel consumption is a prime objective in the automotive industry in order to meet regulatory and customer demands. Variable valve actuation offers many opportunities for improving the spark ignition engine’s performance in areas such as fuel economy and pollutant emissions. Our studies revealed that the ability to control maximum intake valve lift does indeed offer the ability to control intake air mass, but also has the added benefit that it improves the fuel-air mixing process thanks to an increased turbulence, caused by the increased intake flow velocity. This is particularly important at idle and low part loads when low maximum lifts are to be used for improving the fuel economy or for achieving the required power. The paper focuses on the experimental results obtained when approaching idle operation with different intake valve laws. Results indicating the potential of using low intake valve lift for fuel economy and cyclic dispersion improvement are presented in this paper. Full article

An experimental platform was designed and built for testing the thermal performance of a water/steam cavity receiver. The experimental platform was utilized to investigate the start-up performance and operation characteristics of the receiver. The electrical heating mode was chosen to simulate the non-uniform distribution of heat flux on the surface of absorber tubes inside the cavity. During start-up the temperature rise rate and the mass flow rate are considered as control variables. A couple of start-up curves under different working pressures were finally obtained. The results showed that the receiver performed at relatively low thermal efficiencies. The main reason for the low thermal efficiency was attributed to the low steam mass flow rate, which causes a high proportional heat loss. In order to study the relationship between thermal efficiency and mass flow rate, a computational model for evaluating the thermal performance of a cavity receiver was built and verified. This model couples three aspects of heat transfer: the radiative heat transfer inside the receiver, the flow boiling heat transfer inside the absorber tubes and the convection heat transfer around the receiver. The water/steam cavity receiver of the experimental platform was studied numerically. The curve of thermal efficiency versus mass flow rate was obtained to show that the thermal efficiency increases with increasing mass flow rate within a certain range, and the increase is more remarkable at low mass flow rates. The purpose of the present study was to determine an appropriate mass flow rate for the receiver of the experimental platform to ensure its efficient operation. Full article

Efficient high speed propulsion requires exploiting the cooling capability of the cryogenic fuel in the propulsion cycle. This paper presents the numerical model of a combined cycle engine while in air turbo-rocket configuration. Specific models of the various heat exchanger modules and the turbomachinery elements were developed to represent the physical behavior at off-design operation. The dynamic nature of the model allows the introduction of the engine control logic that limits the operation of certain subcomponents and extends the overall engine operational envelope. The specific impulse and uninstalled thrust are detailed while flying a determined trajectory between Mach 2.5 and 5 for varying throttling levels throughout the operational envelope. Full article

This article describes a simple model obtained from a commercial Stirling engine and used for heating a caravan. The Stirling engine has been tested in the lab under different electrical load conditions, and the operating points obtained are presented. As an application of the model, a series of transient simulations was performed using TRNSYS. During these simulations, the caravan is traveling throughout the day and is stationary at night. Therefore, during the night-time hours, the heating system is turned on by means of the Stirling engine. The study was performed for each month of the year in different European cities. The different heating demand profiles for different cities induce variation in the electricity production, as it has been assumed that electricity is only generated when the thermal demand requires the operation of the Stirling system. As a result, a comparison of the expected power generation in different European cities is presented. Full article

The energy conservation achieved by utilizing waste heat in the energy and industrial sectors has became more and more important after the energy crisis in the 1970s because it plays a vital role in the potential energy-efficiency improvement. In this regard, cogeneration (combined heat and power, CHP) systems are thus becoming attractive due to the energy, economic, and environmental policies for pursuing stable electricity supply, sustainable development and environmental pollution mitigation in Taiwan. The objective of this paper is to present an updated analysis of CHP systems in Taiwan during the period from 1990 to 2010. The description in the paper is thus based on an analysis of electricity supply/consumption and its sources from CHP systems during the past two decades, and centered on two important regulations in compliance with CHP systems (i.e., Energy Management Law and Environmental Impact Assessment Act). Based on the total net power generation from CHP systems (i.e., 35,626 GWh) in 2011, it was found that the carbon dioxide reduction benefits were estimated to be around 20,000 Gg. Full article

Municipal solid waste (MSW) is an important energy resource for combined heat and power (CHP) production. This study summarized an overview of CHP by MSW to energy (WtE) plants in South Korea and discussed the issues related to energy efficiency improvement. Given the dominant housing culture of apartment living in South Korea, the primary energy output of WtE plants has been for district heating. In 2010, approximately half of the 51 large WtE plants were CHP, while the rest produced heat. Power generation in the WtE CHP plants was estimated to be only 3.65% of the thermal input, while heat production was 60.79%. The R1 efficiency when compared to that in Europe was similar for the CHP plants and higher for heat-only plants. Improving power generation efficiency is required for new power plants producing steam at pressures higher than the current level of 20–30 bar. Over ten of the existing plants needed to increase their energy efficiency by installing new equipment such as steam turbines for excess steam. Finally, transboundary centralization of WtE plants between neighboring local authorities is essential for heat utilization since many existing small-scale plants (<50 t/day capacity) do not recover heat. Full article