Analysis of exhaust waste heat recovery from a dual fuel low temperature combustion engine using an Organic Rankine Cycle

This paper examines the exhaust waste heat recovery potential of a high-efficiency, low-emissions dual fuel low temperature combustion engine using an Organic Rankine Cycle (ORC). Potential improvements in fuel conversion efficiency (FCE) and specific emissions (NO_x and CO₂) with hot exhaust gas recirculation (EGR) and ORC turbocompounding were quantified over a range of injection timings and engine loads. With hot EGR and ORC turbocompounding, FCE improved by an average of 7 percentage points for all injection timings and loads while NO_x and CO₂ emissions recorded an 18 percent (average) decrease. From pinch-point analysis of the ORC evaporator, ORC heat exchanger effectiveness (?), percent EGR, and exhaust manifold pressure were identified as important design parameters. Higher pinch point temperature differences (PPTD) uniformly yielded greater exergy destruction in the ORC evaporator, irrespective of engine operating conditions. Increasing percent EGR yielded higher FCEs and stable engine operation but also increased exergy destruction in the ORC evaporator. It was observed that hot EGR can prevent water condensation in the ORC evaporator, thereby reducing corrosion potential in the exhaust piping. Higher ? values yielded lower PPTD and higher exergy efficiencies while lower ? values decreased post-evaporator exhaust temperatures below water condensation temperatures and reduced exergy efficiencies.     

Assessment of hydrogen production from waste heat using hybrid systems of Rankine cycle with proton exchange membrane/solid oxide electrolyzer

A techno-economic assessment of hydrogen production from waste heat using a proton exchange membrane (PEM) electrolyzer and solid oxide electrolyzer cell (SOEC) integrated separately with the Rankine cycle via two different hybrid systems is investigated. The two systems run via three available cement waste heats of temperatures 360 °C, 432 °C, and 780 °C with the same energy input. The waste heat is used to run the Rankine cycle for the power production required for the PEM electrolyzer system, while in the case of SOEC, a portion of waste heat energy is used to supply the electrolyzer with the necessary steam. Firstly, the best parameters; Rankine working fluid for the two systems and inlet water flow rate and bleeding ratio for the SOEC system are selected. Then, the performance of the two systems (Rankine efficiency, total system efficiency, hydrogen production rate, and economic and CO₂ reduction) is investigated and compared. The results reveal that the two systems' performance is higher in the case of steam Rankine than organic, while a bleeding ratio of 1% is the best condition for the SOEC system. Rankine output power, total system efficiency, and hydrogen production rate rose with increasing waste heat temperature having the same energy. SOEC system produces higher hydrogen production and efficiency than the PEM system for all input waste heat conditions. SOEC can produce 36.9 kg/h of hydrogen with a total system efficiency of 23.8% at 780 °C compared with 27.4 kg/h and 14.45%, respectively, for the PEM system. The minimum hydrogen production cost of SOEC and PEM systems is 0.88 $/kg and 1.55 $/kg, respectively. The introduced systems reduce CO₂ emissions annually by about 3077 tons.     

Cycle variations in a hydrogen internal combustion engine

The cycle variation characteristics of a port fuel injection hydrogen internal combustion engine (PFI-HICE) have been extensively investigated. The covariance of indicated mean effective pressure (COV_imep) is the best parameter for evaluating the cycle variations in the PFI-HICE. COV_imep decreases as fuel–air ratio increases from 1000 to 5500 rpm, and engine speed minimally affects COV_imep. The effect of ignition advance angle on COV_imep is determined by fuel–air ratio. The ignition advance angles that correspond to the minimum COV_imep of the PFI-HICE decrease as fuel–air ratio increases. The effect of ignition advance angle on COV_imep diminishes as fuel–air ratio increases. The COV_imep of the PFI-HICE rapidly decreases as throttle increases when the throttle is less than 20%. Injection timing only slightly affects COV_imep under high-speed conditions, and COV_imep increases when hydrogen is injected in intake periods under low-speed conditions. These results indicate that studying COV_imep improves the stability of PFI-HICEs.     

Performance of a combined organic Rankine cycle and vapor compression cycle for heat activated cooling

Heat activated cooling has the potential of utilizing thermal sources that currently go unused such as engine exhaust heat or industrial waste heat. Using these heat sources can provide enhanced energy utilization and reduced fuel usage in applications where cooling is needed. The concept developed here uses waste heat from stationary and mobile engine cycles to generate cooling for structures and vehicles. It combines an organic Rankine cycle (ORC) with a conventional vapor compression cycle. A nominal 5 kW cooling capacity prototype system was developed based on this concept and tested under laboratory conditions. In order to maintain high system performance while reducing size and weight for portable applications, microchannel based heat transfer components and scroll based expansion and compression were used. Although the system was tested off of its design point, it performed well achieving 4.4 kW of cooling at a measured heat activated COP of 0.48. Both the conversion and 2nd law efficiencies were close to the model results, proving it to be an attractive technology. The measured isentropic efficiency of the scroll expander reached 84%, when the pressure ratio was close to the scroll intrinsic expansion ratio. The reduced cooling capacity was attributed to off design operation.     

Parametric optimization and performance analysis of a waste heat recovery system using Organic Rankine Cycle

Parametric optimization and performance analysis of a waste heat recovery system based on Organic Rankine Cycle, using R-12, R-123 and R-134a as working fluids for power generation have been studied. The cycles are compared with heat source as waste heat of flue gas at 140 °C and 312 Kg/s/unit mass flow rate at the exhaust of ID fans for 4 × 210 MW, NTPC Ltd. Kahalgaon, India. Optimization of turbine inlet pressure for maximum work and efficiencies of the system along the saturated vapour line and isobaric superheating at different pressures has been carried out for the selected fluids. The results show that R-123 has the maximum work output and efficiencies among all the selected fluids. The Carnot efficiency for R-123 at corrected pressure evaluated under similar conditions is close to the actual efficiency. It can generate 19.09 MW with a mass flow rate of 341.16 Kg/s having a pinch point of 5 °C, First law efficiency of 25.30% and the Second law efficiency of 64.40%. Hence selection of an Organic Rankine Cycle with R-123 as working fluid appears to be a choice system for utilizing low-grade heat sources for power generation.     

A highly efficient six-stroke internal combustion engine cycle with water injection for in-cylinder exhaust heat recovery

A concept adding two strokes to the Otto or Diesel engine cycle to increase fuel efficiency is presented here. It can be thought of as a four-stroke Otto or Diesel cycle followed by a two-stroke heat recovery steam cycle. A partial exhaust event coupled with water injection adds an additional power stroke. Waste heat from two sources is effectively converted into usable work: engine coolant and exhaust gas. An ideal thermodynamics model of the exhaust gas compression, water injection and expansion was used to investigate this modification. By changing the exhaust valve closing timing during the exhaust stroke, the optimum amount of exhaust can be recompressed, maximizing the net mean effective pressure of the steam expansion stroke (MEP_steam). The valve closing timing for maximum MEP_steam is limited by either 1 bar or the dew point temperature of the expansion gas/moisture mixture when the exhaust valve opens. The range of MEP_steam calculated for the geometry of a conventional gasoline engine and is from 0.75 to 2.5 bars. Typical combustion mean effective pressures (MEP_combustion) of naturally aspirated gasoline engines are up to 10 bar, thus this concept has the potential to significantly increase the engine efficiency and fuel economy.     

The distinctive characteristics of combustion duration in hydrogen internal combustion engine

As a practical solution to reduce the emission pollution and energy crisis, the research and development of HICE has been processed in several decades. The focus of this paper is trying to explore the new features of the combustion duration in HICE not only by engine experiment, but also by analysis of the physical properties of hydrogen, especially the obvious difference from that of gasoline. Firstly, the laminar flame speed difference between hydrogen and gasoline was studied and discussed. Secondly, a distinctive rule of combustion duration in HICE was discovered by analyzing the experiment data. Finally, as a key reference point to the HICE operation, a new characteristic of the location of 50% mixture combust up was proposed and analyzed, this will be helpful for the calibration of optimum ignition timing.     

补燃型不可逆联合循环热机的性能分析

在原有的不可逆联合动力循环模型的基础上,建立了一个存在热阻、热漏、补燃、内不可逆性的定常流联合卡诺热机循环模型。研究其在补燃作用下的功率和效率特性并对其进行优化,导出功率、效率的基本优化关系,分析了补燃对最优性能的影响。     

An onboard hydrogen generator for hydrogen enhanced combustion with internal combustion engine

Hydrogen enhanced combustion (HEC) for internal combustion engine is known to be a simple mean for improving engine efficiency in fuel saving and cleaner exhaust. An onboard compact and high efficient methanol steam reformer is made and installed in the tailpipe of a vehicle to produce hydrogen continuously onboard by using the waste heat of the engine for heating up the reformer; this provides a practical device for the HEC to become a reality. This use of waste heat from engine enables an extremely high process efficiency of 113% to convert methanol (8.68 MJ) for 1.0 NM of hydrogen (9.83 MJ) and low cost of using hydrogen as an enhancer or as a fuel itself. The test results of HEC from the onboard hydrogen production are presented with 2 gasoline engine vehicles and 2 diesel engines; the results indicate a hike of engine efficiency in 15–25% fuel saving and a 40–50% pollutants reduction including 70% reduction of exhaust smoke. The use of hydrogen as an enhancer brings about 2–3 fold of net reductions in energy, carbon dioxide emission and fuel cost expense over the input of methanol feed for hydrogen production.     

The characteristic of polytropic coefficient of compression stroke in hydrogen internal combustion engine

The polytropic coefficient has important effect on the calculation of the instantaneous heat release rate and its comparison with specific heat ratio contains the information of the gas-surroundings heat exchange. This article studies the polytropic coefficient characteristics from 1000 rpm to 5000 rpm and the equivalence ratio from 0.24 to 0.55 by using experimental data from a 2.0 L hydrogen engine. The polytropic coefficient increase from 1.3 to 1.35 with the increase of engine speed from 1000 rpm to 4000 rpm, and then it decrease to around 1.34. This characteristic can be used to calculate the heat release rate more accurately. The study of the effect of equivalence ratio suggested that the polytropic coefficient decreased with the increase of equivalence ratio. The polytropic coefficient of hydrogen engine ranges from 1.28 to 1.35, which is less than the gasoline of 1.32–1.4. And the rising period of polytropic coefficient of ‘hydrogen – 0.55’ at 4500 rpm is very longer than others, which showed that the gases properties had effect on the heat transfer. These characteristics could not only be used for heat transfer calculation, but they can also enrich the research of polytropic coefficient for hydrogen internal combustion engine.     

Fundamental experiment of pumpless Rankine-type cycle for low-temperature heat recovery

This paper proposes a new pumpless Rankine-type cycle for power generation from low-temperature heat sources. The new cycle mainly consists of an expander, two heat exchangers, and switching valves for the expander and heat exchangers. Instead of using a working fluid pump, the switching valves method (SVM) is employed to control the cycle. The SVM makes each heat exchanger switch between functioning as an evaporator and functioning as a condenser. In this arrangement, the working fluid flows back and forth between the two heat exchangers without a working fluid pump. Therefore, the new cycle does not involve problems caused by a pump. In the first basic experiment carried out to clarify the feasibility of the proposed cycle, the function of the expander was emulated by using an expansion nozzle. HFC245fa was used as the working fluid. The experimental results confirm that the proposed cycle works and that it has the potential to produce power. Fundamental time-varying characteristics of the proposed cycle are also shown and discussed.     

Second law analysis of a diesel engine waste heat recovery with a combined sensible and latent heat storage system

The exhaust gas from an internal combustion engine carries away about 30% of the heat of combustion. The energy available in the exit stream of many energy conversion devices goes as waste. The major technical constraint that prevents successful implementation of waste heat recovery is due to intermittent and time mismatched demand for and availability of energy. The present work deals with the use of exergy as an efficient tool to measure the quantity and quality of energy extracted from a diesel engine and stored in a combined sensible and latent heat storage system. This analysis is utilized to identify the sources of losses in useful energy within the components of the system considered, and provides a more realistic and meaningful assessment than the conventional energy analysis. The energy and exergy balance for the overall system is quantified and illustrated using energy and exergy flow diagrams. In order to study the discharge process in a thermal storage system, an illustrative example with two different cases is considered and analyzed, to quantify the destruction of exergy associated with the discharging process. The need for promoting exergy analysis through policy decision in the context of energy and environment crisis is also emphasized.     

Backfire prediction in a manifold injection hydrogen internal combustion engine

Hydrogen internal combustion engine (H2ICE) easily occur inlet manifold backfire and other abnormal combustion phenomena because of the low ignition energy, wide flammability range and rapid combustion speed of hydrogen. In this paper, the effect of injection timing on mixture formation in a manifold injection H2ICE was studied in various engine speed and equivalence ratio by CFD simulation. It was concluded that H2ICE of manifold injection have an limited injection end timing in order to prevent backfire in the inlet manifold. Finally, the limit of injection end timing of the H2ICE was proposed and validated by engine experiment.     

Parametric analysis of a hybrid power system using organic Rankine cycle to recover waste heat from proton exchange membrane fuel cell

Using fuel cell systems for distributed generation (DG) applications represents a meaningful candidate to conventional plants due to their high power density and the heat recovery potential during the electrochemical reaction. A hybrid power system consisting of a proton exchange membrane (PEM) fuel cell stack and an organic Rankine cycle (ORC) is proposed to utilize the waste heat generated from PEM fuel cell. The system performance is evaluated by the steady-state mathematical models and thermodynamic laws. Meanwhile, a parametric analysis is also carried out to investigate the effects of some key parameters on the system performance, including the fuel flow rate, PEM fuel cell operating pressure, turbine inlet pressure and turbine backpressure. Results show that the electrical efficiency of the hybrid system combined by PEM fuel cell stack and ORC can be improved by about 5% compared to that of the single PEM fuel cell stack without ORC, and it is also indicated that the high fuel flow rate can reduce the PEM fuel cell electrical efficiency and overall electrical efficiency. Moreover, with an increased fuel cell operating pressure, both PEM fuel cell electrical efficiency and overall electrical efficiency firstly increase, and then decrease. Turbine inlet pressure and backpressure also have effects on the performance of the hybrid power system.     

Backfire control and power enhancement of a hydrogen internal combustion engine

Frequent backfire can occur in inlet port fuel injection hydrogen internal combustion engines (HICEs) when the equivalence fuel–air ratio is larger than 0.56, thus limiting further enhancement of engine power. Thus, to control backfire, an inlet port fuel injection HICE test system and a computational fluid dynamics model are established to explore the factors that cause backfire under high loads. The temperature and the concentration of the gas mixture near the intake valves are among the essential factors that result in backfire. Optimizing the timing and pressure of hydrogen injection reduces the concentration distribution of the intake mixture and the temperature of the high-concentration mixture through the inlet valve, thus allowing control of backfire. Controlling backfire enables a HICE to work normally at high equivalence fuel–air ratio (even beyond 1.0). A HICE with optimized hydrogen injection timing and pressure demonstrates significant enhancement of the power output.     

Dynamic modeling and optimal control strategy of waste heat recovery Organic Rankine Cycles

Organic Rankine Cycles (ORCs) are particularly suitable for recovering energy from low-grade heat sources. This paper describes the behavior of a small-scale ORC used to recover energy from a variable flow rate and temperature waste heat source. A traditional static model is unable to predict transient behavior in a cycle with a varying thermal source, whereas this capability is essential for simulating an appropriate cycle control strategy during part-load operation and start and stop procedures. A dynamic model of the ORC is therefore proposed focusing specifically on the time-varying performance of the heat exchangers, the dynamics of the other components being of minor importance. Three different control strategies are proposed and compared. The simulation results show that a model predictive control strategy based on the steady-state optimization of the cycle under various conditions is the one showing the best results.     

Theoretical thermodynamic analysis of Rankine power cycle with thermal driven pump

A new approach to improve the performance of supercritical carbon dioxide Rankine cycle which uses low temperature heat source is presented. The mechanical pump in conventional supercritical carbon dioxide Rankine cycle is replaced by thermal driven pump. The concept of thermal driven pump is to increase the pressure of a fluid in a closed container by supplying heat. A low grade heat source is used to increase the pressure of the fluid instead of a mechanical pump, this increase the net power output and avoid the need for mechanical pump which requires regular maintenance and operational cost. The thermal driven pump considered is a shell and tube heat exchanger where the working fluid is contained in the tube, a tube diameter of 5 mm is chosen to reduce the heating time. The net power output of the Rankine cycle with thermal driven pump is compared to that of Rankine cycle with mechanical pump and it is observed that the net power output is higher when low grade thermal energy is used to pressurize the working fluid. The thermal driven pump consumes additional heat at low temperature (60 °C) to pressurize the working fluid.     

Effect of water injection and spark timing on the nitric oxide emission and combustion parameters of a hydrogen fuelled spark ignition engine

One of the main problems with hydrogen fuelled internal combustion engines is the high NO level due to rapid combustion. Use of diluents with the charge and retardation of the spark ignition timing can reduce NO levels in Hydrogen fuelled engines. In this work a single cylinder hydrogen fuelled engine was run at different equivalence ratios at full throttle. NO levels were found to rise after an equivalence ratio of 0.55, maximum value was about 7500 ppm. High reductions in NO emission were not possible without a significant drop in thermal efficiency with retarded spark ignition timings. Drastic drop in NO levels to even as low as 2490 ppm were seen with water injection. In spite of the reduction in heat release rate (HRR) no loss in brake thermal efficiency (BTE) was observed. There was no significant influence on combustion stability or HC levels.     

Finding a suitable catalyst for on-board ethanol reforming using exhaust heat from an internal combustion engine

Ethanol steam reforming with pure ethanol and commercial bioethanol (S/C = 3) was carried out inside the housing of the exhaust gas pipe of a gasoline internal combustion engine (ICE) by using exhaust heat (610–620 °C). Various catalytic honeycombs loaded with potassium-promoted cobalt hydrotalcite and with ceria-based rhodium–palladium catalysts were tested under different reactant loads. The hydrogen yield obtained over the cobalt-based catalytic honeycomb at low load (F/W < 25 mL_liq·g_cat^?1·h^?1, GHSV = 4·10² h^?1) was remarkably high, whereas that obtained over the noble metal-based catalytic honeycombs was much superior at high loads (F/W = 25–150 mL_liq·g_cat^?1·h^?1, GHSV = 4·10²–2.4·10³ h^?1). At higher reactant loads the overall hydrogen production was limited by heat transfer from the exhaust heat to the reformer inside the housing of the exhaust gas pipe of the ICE. Extensive carbon deposition occurred over the cobalt-based honeycomb, making its use impractical. In contrast, stability runs (>200 h) at high load (F/W = 150 mL_liq·g_cat^?1·h^?1, GHSV = 2.4·10³ h^?1) showed that promotion of the ceria-supported noble metal catalyst with alumina and zirconia is a key element for practical application using commercial bioethanol. HRTEM analysis of post mortem honeycombs loaded with RhPd/Ce_0.5Zr_0.5O₂–Al₂O₃ showed no carbon formation and no metal agglomeration.     

内燃机冷热电联产系统设计点性能分析

简介内燃机冷热电联产系统的发展现状,总结了发电用内燃机在设计点工况下主要参数的现有分布范围:排气温度约为450~600℃,排气流量基本上与额定功率呈线性关系,发电效率一般在33%~45%。对联产系统不同形式的能量输出、联产系统经济效率等进行分析研究,表明联产系统回收的能量主要来自排气和冷却水,排气回收能量一般高于冷却水回收能量。与热电联产系统相比,由于制冷比供热困难,冷热电联产系统的经济效率较高。