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CO2 transcritical power cycle (CTPC) systems have attracted considerable research focus in the fields of thermoelectric conversion and waste heat recovery. The regenerator is a key component affecting the CTPC system's efficiency. To improve the comprehensive performance of the regenerator, extensive research has been conducted to optimize the regenerator flow channel design. However, the optimization of the traditional Z-channel printed circuit heat exchanger structure (ZPCHE) is limited to constant cross-sectional configurations along the flow direction, which can lead to low channel space utilization. To solve this problem, an efficient variable cross section Z-channel structure (UAPCHE) is proposed in this study. The structure is designed with different cross-sectional shapes along the flow direction to fit the flow path of the main fluid. UAPCHE achieves a coordinated optimization of the heat transfer (Nu), flow (dP), and compactness performance (Q/V) by increasing the effective utilization of the channel space and weakening the damage to the fluid boundary layer. The design principle of the UAPCHE is introduced, and based on this, the structural parameters of the UAPCHE are optimized to achieve the best comprehensive performance. The results show that, compared with the ZPCHE, Nu of UAPCHE can be increased by 16.79%, dP can be reduced by 19.48%, and Q/V can be increased by 22.65%. [ABSTRACT FROM AUTHOR] more...

In this study, the influence of direct steam injection (DSI) on the performance and emissions of marine engines is investigated. Simulation models are developed and tested based on experimental data. Steam is obtained by waste heat recovery in a marine engine. The limitations of DSI parameters are investigated based on the exhaust gas temperature. The steam quantity and temperature decrease with a decrease in load. The results show that steam mass plays an important role in NOx reduction and improving power. For a steam/fuel ratio of 1.27 at 100% load, the brake power improved by 3.09% and NOx emissions decreased by 4.67%. A higher degree of improvement is obtained with an increase in steam mass. The steam temperature and injection timing only slightly influenced the brake power and NOx emissions. When steam-injection timing improved to 12°CA at 100% load with injection duration decreasing from 85°CA to 25°CA, brake power improved from 3,485.7 to 3,529.7 kW. All of this demonstrates that the DSI approach has excellent energy-saving and emission reduction potential for marine engines. The steam-injection strategy should be optimized in the future. [ABSTRACT FROM AUTHOR] more...

The organic Rankine cycle (ORC), as the most promising technology for engine waste heat recovery, has many configurations available to match the complicated engine waste heat conditions. This paper is aimed at revealing the characteristics of the engine waste heat condition for which different ORC configurations are matched so as to give selection guidance. The engine waste heat sources are characterized by the exhaust gas temperature (300°C-650°C) and the heat ratio of the high temperature waste heat to low temperature waste heat (0.5-1.5). Four mostly investigated configurations including the single-loop ORC, the cascade dual-loop ORC, the dual-pressure ORC, and the CO2 transcritical Rankine cycle (CTRC) are selected and modified to enable efficient utilization of all waste heat sources. Their thermodynamic performance is optimized for different waste heat characteristics. The results show improvements in net power for all configurations when exhaust gas temperature and heat ratio rise from 300°C, 0.5, to 650°C, 1.5, respectively, of which the high-temperature split CTRC (HTS-CTRC) recorded the largest increase of 183.58%, while the split regenerative ORC (SR-ORC), dual-pressure ORC (D-ORC), and split cascade ORC (SC-ORC) increased by 17.41%, 23.71%, and 35.45%, respectively. Two selection maps are established to provide general references for quickly selecting the configuration according to different waste heat characteristics whatever the engine type and operating conditions. [ABSTRACT FROM AUTHOR] more...

Water/steam direct injection is an effective method to lower emissions and improve the power of engines by using waste heat recovery (WHR). The parameters of water injection (WI) and steam injection (SI) were analyzed at compression stroke on the effect of brake power and emissions in marine engines, including injected timing, mass, and temperature. The results demonstrated that NOx emissions were substantially reduced by using WI method. However, brake power was also decreased. The SI method not only decreased NOx emissions but also improved brake power. The NOx emissions were ascended with increasing temperature and delaying injected timing of water. Opposing trends were found for SI method. The injected mass has a large effect on power and emissions compared with the influence of temperature and timing. The NOx emissions can be reduced by 72.8% with 2.08% power loss when the 20 g of water was injected into the cylinder at −50 °CA, 15 bar and 400 K. The NOx emissions can be reduced by 38.9% with 24.7% power improvement when the same mass of superheated steam with 500 K of temperature was injected into the cylinder. It can be obvious that SI method can increase power while reducing fuel consumption and emissions. [ABSTRACT FROM AUTHOR] more...

In this paper, a brief review and comparison of the engine waste heat recovery technologies have been made. These five technologies are electric turbocompounding systems (ETC), thermodynamic organic Rankine cycle (ORC), thermoelectric generators (TEG), hydrogen generation by using exhaust gas heat energy, and hybrid pneumatic power systems (HPPS). According to comparison results, the HPPS system can achieve the highest fuel economy improvement among the five technologies. Though there are their own benefits by utilizing these different technologies, their disadvantages prevent the application of these advanced technologies to different extent. Besides, a combined evaluation method consisting of grey relational analysis and analytic hierarchy process has been applied to assess the five new engine waste heat recovery technologies from the perspective of technical, economic, and environmental aspect. Based on the final results of the new evaluation method, the HPPS was found to be the most promising WHR technology for vehicle engines. But because of the emphasis on economic benefit, TEG was found to be more favorable for working conditions, like power plant and marine engine. What is more, as is shown in the sensibility analysis, the weighing of the environment relevant factors can prominently influence the comparison results between ETC and HPPS. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR] more...

• In-cylinder direct steam injection (CDSI) and two steam expansion cylinders (TSEC) were compared. • The CDSI method can increase engine power and reduce emissions. • TSEC requires more steam to improve engine performance than CDSI. • The CDSI method is an effective way to reduce fuel consumption and engine emission. In the present study, the steam utilization mode was discussed based on a gasoline engine. The thermodynamic processes of two steam utilization modes were investigated based on the validated model. And, the effects of in-cylinder direct steam injection (CDSI) and two steam expansion cylinders (TSEC) on engine performance were studied. The results show that the firing cylinder temperature decreases with both CDSI and TSEC engines. However, the in-cylinder pressure increases for the CDSI-engine. The CDSI method can greatly benefit engines from an emissions perspective, as it reduces NO x , HC, and CO by 79.0 %, 2.4 %, and 17.6 % respectively. It is worth noting that the TSEC method cannot improve engine performance through waste heat recovery. The results also demonstrate that the indicated power of the TSEC-engine is higher that the results achieved by using the CDSI method when the steam injection quantity is greater than 0.80 g. All these demonstrate that CDSI approach has great potential for application in gasoline engines. The present results provide strong evidence for the application in gasoline engines. [ABSTRACT FROM AUTHOR] more...

The Rankine cycle serves as a crucial technical tool for waste-heat recovery. Matching heat sources and working fluids presents a challenging problem among the extensive research on the process design and selection of working fluids for the Rankine cycle. This study introduces a process design methodology for the Rankine cycle based on heat matching. It can optimize the performance between heat sources and working fluids without the need to preset the configuration for the cycle. The objective is to ultimately derive the most efficient configuration and operating conditions for the Rankine cycle. This method relies on establishing a matching relationship between temperature and heat diagram curves of both heat sources and working fluids. The relationship can be described by a simple linear programming problem, serving as the fundamental model for the proposed method. Demonstration of the feasibility and accuracy of this method involved computing the performance of a subcritical Rankine cycle for waste heat recovery in an ammonia-diesel dual-fuel engine. Three different working fluids were considered: ammonia, R123, and R245fa. Ammonia exhibited superior performance with an overall system efficiency improvement of 5.18 %, surpassing R123 (5.01 %) and R245fa (5.00 %). The competitiveness of the ammonia Rankine cycle has been established, resulting in a nearly zero-carbon-emission power system potentially achieving an overall efficiency of 53.23 %. The process design method based on heat matching notably reduces the modeling efforts required for the Rankine cycle. This reduction provides substantial support for engineering design and facilitates wider applications of the Rankine cycle. [Display omitted] • Establish a concise Process design method for Rankine cycle based on heat matching. • Optimize heat matching using linear programming. • Zero carbon ammonia Rankine cycle is more suitable for ammonia engines. [ABSTRACT FROM AUTHOR] more...

With urging needs to decrease the fuel consumption and environment pollution, energy saving and emission reduction technologies in the ICE (internal combustion engine) industry are developed. A thermal OS/ORC (Oil Storage/Organic Rankine Cycle) system was constructed and preliminarily tested for WHR (Waste Heat Recovery) from exhaust gas of a 240 kW diesel engine. The heat balance test of diesel engine without OS/ORC was conducted first to investigate the varying property of exhaust gas, then the OS/ORC system was tested to show its ability against high temperature and variation of exhaust gas. The results show that thermal oil effectively dropped the working temperature of organic fluid to less than 210 °C, which is much lower than the decomposition temperature of many organic fluids. Also, thermal oil brought a significant inertia to the response of system which could be positive against the variation of engine condition. In order to learn more about the operating characteristics of OS/ORC system, the impact of important parameters on each other was investigated quantitatively as well as on the performance of OS/ORC system. The results show that within the given range, higher evaporating pressure can obviously improve the performance of OS/ORC while the impact of superheat is nearly negligible. [ABSTRACT FROM AUTHOR] more...

For high temperature ORC (Organic Rankine Cycle) used in engine waste heat recovery, it's very critical to select a high temperature working fluid. HCs (Hydrocarbons) usually have excellent cycle performance, but the flammability limits their practical application. Considering that some retardants can be used to suppress flammability, the paper presents an application of mixtures based on hydrocarbons blending with refrigerant retardants to engine waste heat ORC. Three pure hydrocarbons (cyclopentane, cyclohexane, benzene) and two retardants (R11, R123) are selected for combination. Thermal efficiency and exergy loss are selected as the main objective functions. Based on thermodynamic model, the effects of retardants mass fraction, evaporation temperature and IHE (internal heat exchanger) are investigated. Results show that zeotropic mixtures do have higher thermal efficiency and lower exergy loss than pure fluids, at a certain mixture ratio. There exists the OMR (optimal mixture ratio) for different mixtures, and it changes with the evaporation temperature. When adding IHE to system, cycle performance could be obviously improved, and for benzene/R11 (0.7/0.3), the efficiency growth is about 7.12%∼9.72%. Using it, the maximum thermal efficiency of the system can achieve 16.7%, and minimum exergy loss is only 30.76 kW. [ABSTRACT FROM AUTHOR] more...

Highlights: [•] Less complex fluids are preferred due to their excellent performances. [•] The cyclic Alkanes are considered as the most promising candidate. [•] Maximum improvement of 10% in BSFC is obtained by DE-ORC combined systems. [•] Alkane-based ORCs may be more attractive than steam cycle for exhaust heat recovery. [ABSTRACT FROM AUTHOR] more...

Highlights: [•] A novel electricity–cooling cogeneration system was used to recover waste heat aboard ships. [•] Performance of such RC–ARS system was investigated theoretically. [•] Optimal exergy output can be obtained when the vaporization pressure of RC is 300kPa. [•] The exergy efficiency of cogeneration system is 5–12% higher than that of basic Rankine cycle only. [ABSTRACT FROM AUTHOR] more...

Abstract: The paper analyzes the combined TEG-ORC (thermoelectric generator and organic rankine cycle) used in exhaust heat recovery of ICE (internal combustion engine) theoretically. A theoretical model is proposed to calculate the optimal parameters of the bottoming cycle based on thermodynamic theory when net output power and volumetric expansion ratio are selected as objective functions, which affect system performance and size. The effects of relative TEG flow direction, TEG scale, highest temperature, condensation temperature, evaporator pressure and efficiency of IHE (internal heat exchanger) on system performance are investigated. R123 is chosen among the fluids whose decomposition temperature exceeds 600 K to avoid fluid resolving and resulting in wet stroke when expansion process ends. The thermodynamic irreversibility that occurs in evaporator, turbine, IHE, condenser, pump and TEG is revealed at target working areas. The results indicate a significant increase of system performance when TEG and IHE are combined with ORC bottoming cycle. It is also suggested that TEG-ORC system is suitable to recovering waste heat from engines, because TEG can extend the temperature range of heat source and thereby improve the security and fuel economy of engines. [Copyright &y& Elsevier] more...