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An investigation into the lips-guided-flow combustion chamber (LGFC) and Miller cycle was conducted on a highly intensified diesel engine under rated power conditions to improve thermal efficiency. The radius and depth of the chamber bowl and lips were optimized to intensify the guided flow and fuel/air mixing. The experimental and simulated results show that the LGFC had a higher fuel/air mixture quality and quicker combustion rate, leading to a higher indicated power and higher thermal efficiency. A late intake valve closing (LIVC) Miller cycle with a higher expansion ratio of 11 and a lower compression ratio of 8.2 was used to control the energy distribution of the thermodynamic cycle and reduce the mechanical and thermal loads. The results show that the maximum combustion temperature was decreased by about 45 K and the thermal efficiency was improved by 2.1%. The research results are useful to guide the improvement in thermal efficiency through combustion chamber design and Miller cycle application for highly intensified diesel engines. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper introduces the theoretical basis and optimization method of diesel engine working process theory. By comparing two Miller cycle schemes of B20 biodiesel under different load conditions of 1000 rpm (100%, 75%, and 50%), the best Miller cycle scheme and the best Miller degree were found. Then, based on the Miller cycle scheme, its performance was optimized and analyzed, and the best intake timing scheme of the B20 biodiesel engine under different working conditions was obtained. The results show that the performance of B20 biodiesel in variable valve overlap angle Miller cycle is better than that in variable cam profile Miller cycle, and the effect is the best when the Miller degree is 30 °CA. When B20 biodiesel is used under 100% and 50% load conditions, the maximum power under the two loads is in the area near intake valve timing 179 °CAA and exhaust valve timing 174 °CAA, and intake valve timing 224.5 °CAA and exhaust valve timing 119 °CAA, respectively. Fuel consumption, soot emissions, and NOx emissions also have the corresponding best performance intake valve and exhaust valve positions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, the simulation model was established based on GT-Power software, and a scheme using the Miller cycle based on biodiesel was proposed. Taking diesel engine 16V265H as the research object, the accuracy of the simulation model was verified by experiments. Combined with the comparison of physical and chemical characteristics of biodiesel and the experimental analysis of biodiesel under three different combinations, it was concluded that low ratio biodiesel was the best choice to meet the power, economy, and emission performance of diesel. Through the simulation scheme of the two Miller cycles for pure diesel (B0) and biodiesel (B10) under different load conditions at 1000 rpm, the NOx emission performance of pure diesel in a Miller cycle was significantly improved. On this basis, the comprehensive performance of the two Miller cycles was compared with biodiesel. The results showed that both the Miller cycles could reduce NOx emission. Combined with other key performances of a diesel engine, the best scheme to improve the performance of the diesel engine was to burn B10 biodiesel and overlap angle the Miller cycle of the variable valve at 30 °CA. The scheme has guiding significance for the application of the 16V265H diesel engine. [ABSTRACT FROM AUTHOR]

A one-dimensional (1D) simulation calculation model was created using GT-Power software to investigate the effect of an exhaust gas recirculation (EGR) in concert with the Miller cycle on engine fuel economy and using a 1.5 T gasoline direct injection (GDI) engine as the source engine. The engine was tested under partial loading, full loading, and declared working conditions. The results show that under partial load, the Miller cycle could improve engine fuel economy by reducing pumping losses. In the low-speed 1000 r/min full load region, the Miller cycle had a significant effect on increasing the engine fuel economy. When the Miller intensity was −29 °CA, the fuel consumption decreased by a maximum of 10.5%. At medium speeds, 2000 r/min to 3600 r/min, the Miller cycle did not improve fuel economy significantly. For the Miller cycle with late intake valve closure (LIVC), when the EGR rate was about 7%, the fuel consumption was reduced by about 1.3% compared with the original engine at the same EGR rate. When opposed to the original engine without EGR, the fuel consumption was lowered by approximately 3.2 percent. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In recent years, marine engine manufacturers have become increasingly interested in gas engines as an alternative to diesel engines to address rising crude oil prices and environmental regulations. In this study, a 1.6 MW dedicated gas engine was developed based on a diesel engine with bore 220, stroke 300. The developed gas engine had a precombustion chamber and exhibited excellent performance; the brake mean effective pressure was 2.1 MPa at 1000 rpm and NOx emissions were 50 ppm under 15% O2. In particular, it demonstrated excellent fuel economy with a thermal efficiency of 45%, and its carbon dioxide emissions were ~75% of the conventional diesel engines, thus demonstrating greenhouse gas reduction. These results indicate that suitably developed gas engines can provide a low-cost and energy-efficient alternative to diesel engines. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]