Organic Rankine cycle (ORC) is considered as a rational solution to convert thermal energy of low and moderate temperature heat sources into mechanical work, which currently attracts more and more attention as an effective way for internal combustion engine waste heat recovery (ICE-WHR). Traditional design methods for low-temperature ORCs do not adapt to ICE-WHR suitably due to the specific large-gradient temperature drop characteristics of engine waste heats, and corresponding low-temperature organic fluids meeting with thermal matching and thermal decomposition issues for high-temperature exhaust gas recovery. Hence, there have been a great amount of studies focusing on modified ORCs to achieve a better performance from the aspects of cycle and fluid during the past decade, mainly in 2010s. In this paper, relevant researches of these modified ORCs were reviewed and divided into four parts to approach the ideal cycle, which was defined as the best matching cycle to engine waste heats. From paths of fluid and cycle, high-temperature ORCs (HT-ORCs), mixture ORCs (M-ORCs), ORCs combining with extra loops and dual loop ORCs (DORCs) were summarized. The method of temperature-entropy (t-s) map was applied to provide the approaching degree from modified ORCs to the ideal cycle. The study provides valuable information for stakeholders interested in ORC technologies and gives policymakers perspectives regarding different ORC options for ICE-WHR.

A review of modified Organic Rankine cycles (ORCs) for internal combustion engine waste heat recovery (ICE-WHR)

Organic Rankine cycles (ORC) are an effective way to convert low-medium temperature heat to electricity that cannot be used for conventional high-temperature Rankine cycles. Even though there has been many studies of ORC systems over the past few decades, ORC heat sources have received relatively little attention. The heat sources providing energy to the ORC have different characteristics that significantly impact the theoretical analyses and system designs of ORC systems. This paper gives a theoretical categorization of heat sources to give uniform boundary conditions for further theoretical studies on cycle choices and working fluid screening. The ideal cycles for each heat source type are analyzed. Performance metrics are recommended for different heat source ORC systems. The general characteristics of the different heat sources including waste heat from industrial and power systems and geothermal, solar and biomass sources are given with their influences on the ORC systems. Finally, the market characteristics for ORC systems using different heat sources are reviewed with suggestions for future developments of ORC systems.

Categorization and analysis of heat sources for organic Rankine cycle systems

Thermodynamic and economic performances optimization of an organic Rankine cycle system utilizing exhaust gas of a large marine diesel engine

Effective recovery of heavy-duty vehicle waste heat is a key solution toward meeting the increasingly stringent fuel economy and CO2 emission standards. Different from previous publications, this paper presents a preliminary introduction of organic Rankine cycle waste heat recovery (ORC-WHR) in heavy-duty diesel (HDD) vehicle applications in the past decade. It presents a wide range of topics in the HDD vehicle ORC-WHR system development, including system architecture evaluation, heat exchanger selection, expander selection, working fluid selection, power optimization, control strategy evaluation, simulation and experimental work overview, and limiting factors. In the system architecture selection, the tradeoff between fuel savings and system complexity dominates. In the heat exchanger design, besides the heat exchanger efficiency, transient evaporator response is critical factor for the system control and performance. The expander type and configuration is closely coupled to the expander power output type (i.e. electricity or mechanical power). WHR power production is most sensitive to working fluid mass flow rate, with less sensitivities to expander speed and condenser coolant mass flow rate. The integration of ORC-WHR control with engine control shows potential to improve the waste heat recovery system performance. The simulation studies predict higher power recovery levels than that in experimental work (0–60 kW vs. 0–14 kW), which could result from the large number of heat resources, optimistic expander and pump efficiencies and neglected heat losses in the simulations.

A comprehensive review of organic rankine cycle waste heat recovery systems in heavy-duty diesel engine applications

Thermoeconomic multi-objective optimization of a dual loop organic Rankine cycle (ORC) for CNG engine waste heat recovery

Development of a Reduced Chemical Mechanism for Ammonia/N-Heptane Blends

Investigative research of diesel/ethanol advanced combustion strategies: A comparison of Premixed Charge Compression Ignition (PCCI) and Direct Dual Fuel Stratification (DDFS)

Partially replacing diesel with carbon-free ammonia fuel is gaining more interest in tackling the issue of greenhouse gas emissions in freight transportation applications. But in ammonia-diesel dual-fuel engines, the combustion and emissions are of particular complexity, with complicated trade-offs among the rough combustion, the thermal efficiency, and the CO2/N2O/NO+NO2/NH3 emissions. To this end, this paper conducts systematical experimental tests on a modified PFI-DI single-cylinder heavy-duty diesel engine with ammonia injected in the intake manifold and diesel directly injected into the cylinder, containing ammonia energy fraction ranging from 0% to 50%, engine loads from IMEP 0.5 to 1.3 MPa, and sweeping diesel injection timing. Results show that the heat release of ammonia-diesel dual-fuel combustion (ADDC) possesses two exothermic stages, and as the ammonia energy fraction increases, the heat release process of ADDC in the first stage is intensified and that in the second stage is just the opposite, which causes rougher combustion but lower indicated thermal efficiency (ITE). Increasing the ammonia energy fraction also makes NO+NO2 and CO2 emissions reduced but NH3 and N2O emissions increased. N2O emissions with stronger greenhouse gas impact usually offset the reduction of CO2. Advancing diesel injection timing can improve ITE, but the cost is the rapidly increasing PPRR and NO+NO2 emissions. Besides, as the engine load increases, the ignition delay gets shortened and the combustion process becomes concentrated and efficient, the resistance to ammonia in ADDC gets better, and NH3 emissions are reduced at the cost of more NO+NO2 emissions.

Effects of ammonia energy fractions, diesel injection timings, and loads on combustion and emission characteristics of PFI-DI ammonia-diesel engines

Comparison of diesel single/double/triple injection strategies and early/late compression ignition regimes in an ammonia/diesel dual-fuel engine.

The introduced error associated with the contact-type detection for piston surface temperature in combustion engines using coaxial thermocouples and its eliminating algorithm

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