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Using a combined energy cycle based on conventional and/ or clean energy sources can be a suitable option to dominate the limitations in the field of energy. Meanwhile, the select of the prime power source in such processes is a challengeable issue. The selection of the prime power source from renewable sources and in addition the use of system waste heat can lead to enhance power generation. In the present work, an energy system based on conventional energy sources and clean technology is introduced and investigated. The new integrated hybrid energy cycle is composed of Miller cycle engine (MC), alkaline fuel cell (AFC), alkaline electrolyzer, Organic Rankine cycle (ORC) system and Stirling engine. MC and AFC are used as the main power sources of the cycle. On the other hand, ORC and Stirling engine for generating more electricity from the waste heat of the cycle are applied. The electrolyzer embedded in the cycle receives its electricity from the MC and provides the required inputs of the AFC. Although many studies had been done on the integration of various power generation sources with different energy cycles, attempts had not been done to establish a study on the hybrid of MC, AFC, alkaline electrolyzer, Stirling engine and ORC to produce additional electricity. Results revealed that the introduced energy system generates 3.75 kW of electric power. The portion of MC, fuel cell, ORC, and Stirling engine in electric power production is 71.2, 10.8, 9.5 and 8.5%, respectively. However, the alkaline electrolyzer consumes 2.06 kW of power and generates 48.2 g/h of H2fuel. It was also found that the cycle exergy destruction is 3.34 kW. In addition, the use of MC and AFC heat dissipation heat can enhance power generation.

The article is devoted to the study of the possibilities of improving the technical and economic indicators of an internal combustion engine (ICE) through the use of the Miller cycle with a shortened intake. A review of scientific works on the use of the Atkinson cycle and Miller cycle in an internal combustion engine is carried out. A comparative analysis of theoretical cycles: Otto cycle, Atkinson cycle and Miller cycle is carried out. Calculated studies of the influence of the expansion ratio and the pressure increase ratio on the efficiency of the Atkinson cycle have been carried out. The ratios are presented that allow using the Miller cycle with a short inlet to obtain the same theoretical efficiency of the cycle as that of the Atkinson cycle. At the same time, the implementation of the Miller cycle in a real engine design significantly exceeds the possibilities of using the Atkinson cycle. The results of the study showed that the use of the Miller cycle with a shortened intake is preferable, but it must necessarily increase the compression ratio and intake pressure through the use of boost. On the example of real data of the main parameters of the cycle, it is shown that the use of the theoretical Miller cycle can provide a significant up to 12.2% increase in the efficiency of the cycle compared to the Otto cycle. The ratios, conditions and recommendations are presented that allow the effective use of the Miller cycle with a shortened intake in a real engine design.

Diesel engines play a very significant role in the automotive industry, but the total emissions of diesel engines are more than 1.8 times that of petrol engines. It is therefore important for diesel engines to control emissions. Theoretically, the Miller cycle can be used to achieve NOx reductions by changing the effective compression ratio, while it has become increasingly popular in recent years with the increasing maturity of current turbocharging technology. Based on Ricardo WAVE software, this paper analyses the NOx emissions and engine performance of diesel engines by modelling and simulating their operation under different loads with two types of Miller cycles (EIVC and LIVC) at different degrees. Simulation of engines operating under different loads allows a more comprehensive study of the effects of the Miller cycle on the engine, and a specific analysis in the context of the actual engine operating environment. The result is that both versions of the Miller cycle are most effective in reducing NOx emissions at 10% load, showing a maximum reduction of 21% for EIVC and 37% for LIVC. However, as the Miller cycle decreases engine power, the paper further investigates the application of turbocharger systems in the EIVC Miller cycle, with results showing a 32% increase in brake power at 10% load and −25% EIVC Miller cycle degree. Both ethanol-fueled diesel-cycle and Miller cycle engines were also analyzed, and a reduction in NOx emissions was observed, as well as hydrogen engine performance and NOx emissions.

Thermal efficiency and power density improvement are the main research foci of the literature on diesel engines. The Miller cycle is considered to be one of the most promising methods of diesel engine operation. In this study, a fully variable valve timing and lift mechanism (CD-HFVVS) was studied to determine the possibility of a Miller operation. Firstly, the valve seat impact buffer in the mechanism was tested, which proved that the buffer can effectively eliminate the valve seat impact. Then the influences of different speeds and oil temperatures were studied. The results show that the valve opening duration is prolonged when engine speed increases, and the valve lift and duration are reduced while the oil temperature increased. The valve timing and lift can be fully adjusted by changing the oil discharge position and the initial plunger position, which further proves that CD-HFVVS can achieve the performance optimization of the Miller cycle. By using the mechanism, a single cylinder test was performed. By using variable inlet valve timing, the fuel efficiency can be effectively improved and the peak pressure and in-cylinder average temperature can both be suppressed.

This paper assesses the effect of the Miller cycle upon the internal aerodynamics of a motored transparent spark ignition engine via CFD simulation and particle image velocimetry. Since the transparent Miller engine does not allow for measurements in the roof of the combustion chamber, the extraction of information regarding the aerodynamic phenomena occurring here is based on CFD simulation, i.e., the results of the CFD simulation are used to allow for the extrapolation of the experimental data; thus, they are used to complete the picture regarding the aerodynamic phenomena occurring inside the whole cylinder. The results indicate that implementing the early intake valve closing strategy to obtain the Miller cycle has a negative impact on the mean kinetic energy, turbulent kinetic energy, and fluctuating velocity toward the end of the compression stroke, thus affecting, the combustion process. This supports the need to intensify the internal aerodynamics when applying the Miller cycle such that the turbulence degradation is not too big and, consequently, to still gain efficiency in the Miller cycle.

In this paper, validated simulations using Ricardo WAVE have been performed to investigate the effect of the Miller cycle and low-carbon fuels on the performance (power, torque, BTE and BSFC) and emissions of a diesel engine. The results show that the increased Miller cycle effect (larger deviation of the advanced or retarded intake valve closing from the standard intake valve closing time) will decrease NOx, CO and HC emissions, and slightly improve brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) with slight loss in engine performance and increase in soot emissions. An engine running B0 (diesel with 0% Biodiesel in the blend) with a −18% Miller cycle effect has a reduction in NOx of 9% and CO of 4.3% with a decrease of 1.6% in power at the rated engine speed. Using low carbon fuels drastically reduces emissions with reduced BTE and increased BSFC. When used in conjunction, the Miller cycle and low-carbon fuels have an improved effect on both performance and emissions. The optimal results demonstrate that using B60 (60% Biodiesel in the blend) and a −8% Miller effect contributes to a 1.5% improvement in power, 1.2% in BTE, 13.3% in NOx, 38.5% in CO, 8.9% in HC, and 33.0% in soot at a cost of 6.0% increase in BSFC. The results show that it is an easy way to reduce NOx, CO, HC and soot emissions and increase the BTE of the engine by combining Miller cycle and low-carbon fuels.

The current article presents a method to reconstruct the mean velocity field of a cyclic flow for an input parameter value that has not been measured, allowing for the number of tests to be reduced. It is applied to the tumble flow of a gasoline engine following a Miller cycle. New engines often include variable valve timing (VVT) systems to maximize the efficiency of such over-expanded cycles for different operating points. The reconstruction was thus carried out using different offset values of the intake valve lift timing. Experimental data were collected from a transparent engine in an early intake valve closing (EIVC) configuration using particle image velocimetry (PIV). The mean velocity field reconstruction was based on the interpolation of the proper orthogonal decomposition (POD) coefficients. The accuracy of the method was evaluated at different points by comparing the interpolated and the measured flow fields. The accuracy was estimated by calculating the error in the rotation rate of the tumble and the position of its center of rotation. The new mean velocity field set allowed for the position of the tumble’s center of rotation to be closely tracked according to the input parameter and a rotation rate map to be made. Some results on Miller’s cycle could thus be found and the data generated could guide future developments.

This paper focuses on the investigation and optimisation of the Miller cycle, methanol, ethanol and turbocharging when applied to a high-performance gasoline engine. These technologies have been applied both individually and concurrently to test for potential compounding effects. Improvements have been targeted with regards to both emission output and performance. Also assessed is the capability of the engine to operate when exclusively powered by biofuels. This has been carried out numerically using the 1D gas dynamics tool ‘WAVE’, a 1D Navier–Stokes equation solver. These technologies have been implemented within the McLaren M838T 3.8L twin-turbo engine. The Miller cycle early intake valve close (EIVC) improved peak efficiency by 0.17% and increased power output at low and medium loads by 11%. Reductions of 6% for both NOx and CO were also found at rated speed. The biofuels achieved NOx and CO reductions of 60% and 96% respectively, alongside an efficiency increase of 2.5%. Exclusive biofuel use was found to be feasible with a minimum 35% power penalty. Applied cooperatively, the Miller cycle and biofuels were not detrimental to each other, compounding effects of a further 0.05% efficiency and 2% NOx improvements were achieved.

A major issue nowadays that concerns the pollution of the environment is the emissions emerging from heavy-duty internal combustion engines. Such concern is dictated by the fact that the electrification of heavy-duty transport still remains quite challenging due to limitations associated with mileage, charging speed and payload. Further improvements in the performance and emission characteristics of conventional heavy-duty diesel engines are required. One of a few feasible approaches to simultaneously improve the performance and emission characteristics of a diesel engine is to convert it to operate on Miller cycle. Therefore, this study was divided into two stages, the first stage was the simulation of a heavy-duty turbocharged diesel engine (4-stroke, 6-cylinder and 390 kW) to generate data that will represent the reference model. The second stage was the application of Miller cycle to the conventional diesel engine by changing the degrees of intake valve closure and compressor pressure ratio. Both stages have been implemented through the specialist software which was able to simulate and represent a diesel engine based on performance and emissions data. An objective of this extensive investigation was to develop several models in order to compare their emissions and performances and design a Miller cycle engine with an ultimate goal to optimize diesel engine for improved performance and reduced emissions. This study demonstrates that Miller cycle diesel engines could overtake conventional diesel engines for the reduced exhaust gas emissions at the same or even better level of performance. This study shows that, due to the dependence of engine performance on complex multi-parametric operation, only one model achieved the objectives of the study, more specifically, engine power and torque were increased by 5.5%, whilst nitrogen oxides and particulate matter were decreased by 30.2% and 5.5%, respectively, with negligible change in specific fuel consumption and CO2, as average values over the whole range of engine operating regimes.

This contribution is focused on the fuel economy improvement of the Miller cycle under part-load characteristics on a supercharged DI (Direct Injection) gasoline engine. Firstly, based on the engine bench test, the effects with the Miller cycle application under 3000 rpm were studied. The results show that the Miller cycle has different extents of improvement on pumping loss, combustion and friction loss. For low, medium and high loads, the brake thermal efficiency of the baseline engine is increased by 2.8%, 2.5% and 2.6%, respectively. Besides, the baseline variable valve timing (VVT) is optimized by the test. Subsequently, the 1D CFD (Computational Fluid Dynamics) model of the Miller cycle engine after the test optimization at the working condition of 3000 rpm and BMEP (Brake Mean Effective Pressure) = 10 bar was established, and the influence of the combined change of intake and exhaust valve timing on Miller cycle was studied by simulation. The results show that as the effect of the Miller cycle deepens, the engine’s knocking tendency decreases, so the ignition timing can be further advanced, and the economy of the engine can be improved. Compared with the brake thermal efficiency of the baseline engine, the final result after simulation optimization is increased from 34.6% to 35.6%, which is an improvement of 2.9%.

In order to clarify the potential of internal purification methods on medium speed diesel engines to meet the IMO Tier III nitrogen oxide (NOx) emission regulations, combined 1-D engine working cycle simulation and 3-D CFD simulation were conducted to predict the performance and emissions of the engine under different valve close timings, geometric compression ratios, injection timings, and Exhaust Gas Recirculation (EGR) rates. The numerical results show that, as the inlet valve close timing is advanced, NOx is reduced by as much as 27%, but the peak of premixed combustion heat release rate is increased; this can weaken the ability to reduce NOx with the Miller cycle. Moreover, the peak of premixed combustion heat release rate is reduced when the geometric compression ratio is increased to 15.4, and linking with injection timing by delaying 6°CA can further reduce NOx by 55.3% from the baseline. Finally, over 80% NOx reduction can be achieved when the above schemes are combined with over 15% EGR. The NOx and soot can be reduced simultaneously by using moderate Miller cycle combination with moderate EGR, and the results show a large reduction of NOx and moderate reduction of soot. This can be a feasible technical solution to meet Tier III regulations.

The paper presents the results of research on the turbocharged spark ignition engine with additional exhaust expansion in a separate cylinder, which is commonly known as the five-stroke engine. The research engine has been constructed based on the four cylinder engine in which two outer cylinders work as the fired cylinders, while two internally connected inner cylinders constitute the volume of the additional expansion process. The engine represents a powertrain realizing an ultra-expansion cycle. The purpose of the study was to find an effective additional expansion process in the five-stroke engine. Cylinder-pressure indicating measurements were carried out for one of the fired cylinders and the additional expansion cylinder. The study was performed for over 20 different points on the engine operation map. This allowed us to determine a dependence between the pressure indicated in the fired cylinders and in the additional expansion cylinders. A function of the mean pressure indicated in the additional expansion cylinder versus a brake mean effective pressure was also presented. This showed a load threshold from which the work of the cylinders of additional expansion produced benefits for the output of the experimental engine. The issues of mechanical efficiency and effective efficiency of this engine were also discussed.

A new thermodynamic model for turbocharged diesel engines is developed for Miller cycle analysis and optimization. The effects of turbocharger efficiency, Miller degree, combustion mode, and air fuel ratio on engine efficiency, power, and NOx emissions are analyzed by the model. Engine performance is optimized by the thermodynamic model under the constraints of maximum cylinder pressure and NOx emissions. Although the Miller cycle is beneficial for NOx emission control, it has adverse effects on engine thermal efficiency and power without parameter redesign. Turbocharger efficiency is a key factor in highly boosted Miller cycle diesel engines. The trade-off relationships among thermal efficiency, break mean effective pressure, and NOx emissions can be improved remarkably by highly efficient turbochargers. Measures with high geometric compression ratio and boost pressure and intensified Miller degree must be applied to reduce NOx emissions and improve thermal efficiency simultaneously. The results provide guidance in designing a Miller cycle system for turbocharged diesel engines.