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A novel combined power and cooling cycle based on the Organic Rankine Cycle (ORC) and the Compression Refrigeration Cycle (CRC) is proposed. The cycle can be driven by the exhaust heat from a diesel engine. In this combined cycle, ORC will translate the exhaust heat into power, and drive the compressor of CRC. The prime advantage of the combined cycle is that both the ORC and CRC are trans-critical cycles, and using CO₂ as working fluid. Natural, cheap, environmentally friendly, nontoxic and good heat transfer properties are some advantages of CO₂ as working fluid. In this paper, besides the basic combined cycle (ORC-CRC), another three novel cycles: ORC-CRC with an expander (ORC-CRCE), ORC with an internal heat exchanger as heat accumulator combined with CRC (ORCI-CRC), ORCI-CRCE, are analyzed and compared.

The environmental issues combined with the rising of crude oil price have attracted more interest in waste heat recovery of marine engine. Currently, the thermal efficiency of marine diesels only reaches 48~51%, and the rest energy is rejected to the environment. Meanwhile, energy is required when generating electricity and cooling that are necessary for vessels. Hence, the cogeneration system is treated as the promising technology to conform the strict environment regulation while offering a high energy utilization ratio. In this paper, an electricity and cooling cogeneration system combined of Organic Rankine Cycle (ORC) and Absorption Refrigeration Cycle (ARC) is proposed to recover waste heat from marine engine. ORC is applied to recover exhaust waste heat to provide electricity while ARC is used to utilize condensation heat of ORC to produce additional cooling.

The supercritical CO2 power cycle system for waste heat recovery (WHR) of internal combustion engine (ICE) has widely been concerned as a research hotspot. And the expander is a key component in the supercritical CO2 power system. Rolling rotor expander has the following advantages: compact size, light weight, less moving parts, high stability and long service life, which qualify it a very suitable choice for engine’s waste heat recovery system. For a self-designed rolling rotor expander using supercritical CO2 as its working fluid, FLUENT software was used to simulate its internal flow field in this study, obtaining the changes of the internal pressure field and turbulent kinetic energy. The causes of local vortex in the expansion process were analyzed. Under different working conditions of the expander, the change of internal pressure and the distribution of P-V curve were observed, and the work capacity under different inlet pressure was analyzed.

Transcritical Rankine cycle (TRC) is a promising technology for the engine waste heat recovery due to its good temperature matching ability for the waste heat sources. As for the high-temperature engine exhaust, working fluids selection has been an essential issue without a good solution. It was found in this research that mixtures of CO2 and small molecule hydrocarbons are the potential working fluids for the engine waste heat recovery, since they have good chemical stability and thermal performance. Besides, CO2 can be used as the retardant to suppress the flammability of hydrocarbons to ensure safety. In this research, CO2 mixed with five small molecule hydrocarbons are proposed as the working fluids. A thermodynamic model of TRC system is established to evaluate the thermal performance of those mixtures. The effects of mass fraction of CO2, turbine inlet temperature and pressure are investigated. The influence of composition shift is also discussed.

A bottoming waste-heat-recovery (WHR) model based on the Organic Rankine Cycle (ORC) is proposed to recover waste heat from exhaust gas and jacket water of a typical diesel engine (DE). The ORC model is detailed built based upon real structural and functional parameters of each component, and is able to precisely reflect the working process of the experimental ORC system constructed in lab. The DE is firstly tested to reveal its energy balance and the features of waste heat. The bottoming ORC is then simulated based on experimental data from the DE bench test using R245fa and R601a as working fluid. Thermodynamic evaluations are done on key parameters like waste heat recovered, expansion power, pump power loss and system efficiency. Results indicate that maximum expansion power and efficiency of the ORC are up to 18.8kW and 9.6%. Influences of engine condition, fluid mass flow and evaporating pressure on system performance are analyzed and meaningful regularities are revealed.

Gaseous fuel internal combustion engines (gas engines) for electric generating are important primary movers in distributed energy systems. However, the average thermal efficiency of the gas engine is just about 30%-40% and most of the waste heat is discharged by exhaust. So it is very meaningful to recover the exhaust waste heat. Electricity-cooling cogeneration system (ECCS) inclusive of a steam Rankine cycle (RC) and an absorption refrigeration cycle (ARC) is an effective way for recovering exhaust waste heat of gas engine. Partload performance analysis of ECCS is of great significance due to the frequently varied working conditions of gas engines in practical operation. In this paper, an off-design simulation model of ECCS is firstly established by Matlab. Then the effects of the engine working condition on the performance of ECCS are analyzed by this model.

Because of the great resources potential and the feature of low pollution of gaseous fuel, gaseous fuel internal combustion engines (gas engines) have been paid more and more attention. However, their average thermal efficiency is just about 30-40% wasting a huge amount of energy by exhaust, cooling water and so on, so waste heat recovery is very meaningful. Both the RC (steam Rankine Cycle) and the ORC (Organic Rankine Cycle) are regarded as the suitable way of WHR (waste heat recovery) for internal combustion engines. Therein, RC is usually used in large engines. The WHR system is always designed at rated work condition, while the gas engine may often work at different conditions. This makes the property of the waste heat source change, which affects the performance of WHR system, so it is very important to research its performance at variable working conditions.

This paper presents a model system TEG-DORC that employs thermoelectric generator (TEG) as a topping cycle integrated with a dual-loop organic Rankine bottoming cycle (DORC) to recover exhaust heat of internal combustion engine (ICE). The thermodynamic performance of TEG-DORC system is analyzed based on the first and second law of thermodynamics when system net output power Wnet, thermal efficiency ηth, exergy efficiency ηe and volumetric expansion ratio are chosen as objective functions. The model has many parameters that affect combined system performance such as TEG scale, evaporation pressure of high temperature ORC loop (HT loop) Pevp,HT, condensation temperature of HT loop Tcond,HT. It is suggested that HT loop has a vital influence on system performance.