Miller Cycle Engine

Innovative series hybrid vehicles have a small Internal Combustion Engine used as a "range extender". This engine should work at steady conditions whenever is running. Therefore its development is quite different from engines intended to be driven (unsteady working conditions, such as accelerations). For thıs applicatıon the engine development seeks optimisation on a specified speed/load condition. Previous work proved the concept of over-expansion, as a mean to enhance thermal efficiency of spark ignition engines, even beyond the efficiency of common Diesel engines. There are two ways of performing over-expansion through variation of inlet valve timing: early inlet valve closure (EIVC) and late inlet valve closure (LIVC). To further enhance efficiency, these engines should work with lean or extra lean mixtures. which are very sensitive to in-cylinder charge motion. In order to improve fast burning rates at lean conditions one should optimise turbulence at the end of the compression stroke. A small engine geometry and mesh was created in GAMBIT and later FLUENT was used to perform calculations of the in-cylinder fluid dynamics during intake and compression strokes. These calculations were performed with both described over-expanded valve strategies. The results are compared with engine performance data using the same strategies.

Engine manufacturers generally use aftertreatment systems to meet the strict emission criteria on automotive diesel engines. However, those systems operate inefficiently particularly at low-loaded cases of diesel engines since exhaust gas temperatures at aftertreatment inlet remain below 250 o C. For those cases, variable valve timing (VVT) method can be applied to elevate exhaust temperatures and improve aftertreatment emission conversion efficiency. Therefore, in this study, intake valve closing (IVC) timing is advanced and retarded sufficiently from the base condition on a low-loaded diesel engine to increase aftertreatment inlet exhaust temperature above 250 o C.. A specially designed computer program, Lotus Engine Simulation (LES), is utilized to model the diesel engine. Experimental data of a similar study is used for the validation of the simulation. Engine loading (taken as brake mean effective pressure (BMEP)) is kept constant at 2.5 bar by adjusting the fuel injection rate. The results show that there is a considerable exhaust temperature rise (up to 65 o C) at aftertreatment inlet with the method and it is adequate for effective aftertreatment performance (T exhaust > 250 o C). It is also seen that the increase on exhaust temperature is due to the sudden reduction on volumetric efficiency (from 94 % to 65 %). Therefore, there is lower air induction into the cylinders and hence lower pumping losses which result in fuel-efficiency in the system. However, air flow reduction also causes a sharp decrease on the exhaust flow rate which affects the heat capacity of exhaust gases negatively in the system.

This study presents an experimental investigation of the novel combination of a "wave" bowl piston with thermal barrier coatings (TBCs) and Miller cycle intake valve strategies. All experiments were carried out with a single cylinder research engine with fully-flexible valve timing capabilities. The results indicate the wave bowl geometry enables this combination to improve fuel consumption, steady-state engine-out NOₓ emissions, and particulate matter (PM) emissions, improving the NOₓ-PM tradeoff that compromises diesel engine efficiency. These benefits were achieved at the expense of elevated turbocharger efficiency requirements. Three TBCs of varying composition and thickness were tested at seven operating conditions of varying speed and load. TBC performance was highly dependent on volumetric efficiency (VE), as cases with reduced VE increased the heat transfer gradient between the combustion gasses and the combustion chamber. The insulative properties of each TBC dete...

In this review research, the air capacity of four stroke deck's
engine is investigated and studied thoroughly from the considerations of
Introduction; effect of residual-gas temperature; effect of operating conditions
on volumetric efficiency which constitutes the following: Effect of engine size,
engines with similar cylinders, effect of the pressure ratio {𝑃𝑒 /𝑃𝑖}, effect of fuel
injection on volumetric efficiency, effect of design on volumetric efficiency
which in turn includes (i.e. effect of design on {ΔT}); effect of valve overlap;
inlet system design; important general relations; multi cylinder inlet systems;
effect of exhaust pipe length; effect of heat transfer; effect of camshaft on
volumetric efficiency which includes the following: Camshaft profile, the effect
of lift camshaft, duration, lobe separation, overlap and profile; effect of
atmospheric conditions on performance from the following considerations:
Effect of changes in atmospheric temperature, and effect of inlet temperature;
effect of coolant temperature; intake and exhaust system heat transfer; the study
of the influence of valve profile from the following points of view: Types of
valves, poppet valves, inlet valve flow capacity and exhaust valve flow
capacity; the study of the effect of valve or port timing on engine performance
from the viewpoints of the impact of valve events upon engine performance and
emission, the parameters or variable quantities; effects of valve overlap; Valve
peak lift; industry trends; Exhaust Gas Recirculation (EGR) systems; variable
valve timing; phase changing systems; profile switching systems; variable event
timing systems; variable lift systems; and electro-magnetic valve actuation
systems.

In this study, a prototype four-stroke spark ignition engine with four cylinders (two valves per cylinder), with and without turbocharger, as well as variable valve timing system to adjustment of variable valve duration has been investigated. This study covers the effects of intake valve opening (IVO), Intake valve closing (IVC), exhaust valve opening (EVO) and exhaust valve closing (EVC) angles on engine performances and fuel economy. The calculations of engine performance were carried out using the 1-Dimensional simulation with AVL BOOST software. The effects of different valve timing strategies and a combination of them from simulations were analyzed and compared with the reference fixed valve timing cases. It was shown that substantial improvements in fuel consumption and performance can be achieved. The improvements of Indicated Specific Fuel Consumption (ISFC) are remarkable in turbocharged models. Furthermore, we can see the noticeable improvements in torque and power in the naturally aspirated engine.

Recently, there's been a strong drive to improve performance of diesel engines while reducing their greenhouse gases emissions. Techniques like exhaust gas recirculation, turbocharging, and variable valve timing have become widespread. The last technique fine-tunes valve operation based on engine speed, which optimize efficiency and power output while saving fuel. This study zeroes in on a specific 4-cylinder, 4-stroke diesel engine of 1.56liter, GT-Power software is employed to examine a supercharged version and implementing diverse valve lift techniques. The findings are revealing a substantial 30% increase in power output. At 1000 rpm, power rises from 15.1 kW for the standard engine to 19.72 kW for the modified version. For higher engine speeds, the improvements become even more pronounced, reaching a 66% boost compared to the standard configuration. Furthermore, the newly configured engine showcases an impressive 13% decrease in fuelspecific consumption at elevated engine speeds, contributing to enhanced technical performance and fuel efficiency. The numerical model developed in this study holds the potential to aid in the design of novel diesel engines equipped with variable valve timing systems. To lend further support to these findings, experimental validation is recommended.

In this study, a prototype four-stroke spark ignition engine with four cylinders (two valves per cylinder), with and without turbocharger, as well as variable valve timing system to adjustment of variable valve duration has been investigated. This study covers the effects of intake valve opening (IVO), Intake valve closing (IVC), exhaust valve opening (EVO) and exhaust valve closing (EVC) angles on engine performances and fuel economy. The calculations of engine performance were carried out using the 1-Dimensional simulation with AVL BOOST software. The effects of different valve timing strategies and a combination of them from simulations were analyzed and compared with the reference fixed valve timing cases. It was shown that substantial improvements in fuel consumption and performance can be achieved. The improvements of Indicated Specific Fuel Consumption (ISFC) are remarkable in turbocharged models. Furthermore, we can see the noticeable improvements in torque and power in the naturally aspirated engine.

Today, studying the parameters that affected on the gasoline engine performance becomes very important for the popular using of this type of engines. In spite of the previous studies concerning the economic fuel consumption, some aspects still need more investigations. There are many investigations concerning the internal combustion engine performance. In previous researches the effect of valve timing on engine performance and detonation were studied. In this work, the effect of changing exhaust back pressure with variable intake valve timing on the engine performance was theoretically studied. It was found that the fuel consumption decreased and engine performance improved. The validity of the simulation technique was checked by comparing its results with those from experimental results then a good agreement was noticed.

Experimental and numerical analyses of a turbocharged VVA SI engine. • 3D in-cylinder turbulence analyses for various valve strategies and engine speeds. • Validation of a 1D engine model, including sub-models of in-cylinder processes. • Effect of EIVC and LIVC strategies on fuel consumption in two operating points. • A methodology capable to support the virtual calibration of a VVA engine.

The pursuit of increasing the efficiency of internal combustion engines is an ongoing engineering task that requires numerous research efforts. New concepts of injection or combustion systems require preliminary investigation work using research engines. These engines, usually single-cylinder, make it possible to isolate a single variable in a complex combustion mixture preparation process, thus enabling analysis of the changes being made. However, these engines are relatively expensive and their designs are offered by a limited number of manufacturers. The authors of this paper have successfully undertaken the engineering task of modifying an existing research engine cylinder head in such a way as to implement an electronically controlled variable valve timing system of the intake system. The process of reverse engineering, together with design assumptions that finally contributed to the construction of the assumed solution has been described in this paper.

Engine manufacturers generally use aftertreatment systems to meet the strict emission criteria on automotive diesel engines. However, those systems operate inefficiently particularly at low-loaded cases of diesel engines since exhaust gas temperatures at aftertreatment inlet remain below 250 o C. For those cases, variable valve timing (VVT) method can be applied to elevate exhaust temperatures and improve aftertreatment emission conversion efficiency. Therefore, in this study, intake valve closing (IVC) timing is advanced and retarded sufficiently from the base condition on a low-loaded diesel engine to increase aftertreatment inlet exhaust temperature above 250 o C.. A specially designed computer program, Lotus Engine Simulation (LES), is utilized to model the diesel engine. Experimental data of a similar study is used for the validation of the simulation. Engine loading (taken as brake mean effective pressure (BMEP)) is kept constant at 2.5 bar by adjusting the fuel injection rate. The results show that there is a considerable exhaust temperature rise (up to 65 o C) at aftertreatment inlet with the method and it is adequate for effective aftertreatment performance (T exhaust > 250 o C). It is also seen that the increase on exhaust temperature is due to the sudden reduction on volumetric efficiency (from 94 % to 65 %). Therefore, there is lower air induction into the cylinders and hence lower pumping losses which result in fuel-efficiency in the system. However, air flow reduction also causes a sharp decrease on the exhaust flow rate which affects the heat capacity of exhaust gases negatively in the system.

As known, reliable information about underlying turbulence intensity is a mandatory prerequisite to predict the burning rate in quasidimensional combustion models. Based on 3D results reported in the companion part I paper, a quasi-dimensional turbulence model, embedded under the form of "user routine" in the GT-Power™ software, is here presented in detail. A deep discussion on the model concept is reported, compared to the alternative approaches available in the current literature. The model has the potential to estimate the impact of some geometrical parameters, such as the intake runner orientation, the compression ratio, or the bore-to-stroke ratio, thus opening the possibility to relate the burning rate to the engine architecture. Preliminarily, a well-assessed approach, embedded in GT-Power commercial software v.2016, is utilized to reproduce turbulence characteristics of a VVA engine. This test showed that the model fails to predict tumble intensity for particular valve strategies, such LIVC, thus justifying the need for additional refinements. The model proposed in this work is conceived to solve 3 balance equations, for mean flow kinetic energy, tumble vortex momentum, and turbulent kinetic energy (3-eq. concept). An extended formulation is also proposed, which includes a fourth equation for the dissipation rate, allowing to forecast the integral length scale (4-eq. concept). The impact of the model constants is parametrically analyzed in a first step, and a tuning procedure is advised. Then, a comparison between the 3-and the 4-eq. concepts is performed, highlighting the advantages of the 3-eq. version, in terms of prediction accuracy of turbulence speed-up at the end of the compression stroke. An extensive 3-eq. model validation is then realized according to different valve strategies and engine speeds. The user-model is then utilized to foresee the effects of main geometrical parameters analyzed in part I, namely the intake runner orientation, the compression ratio, and the bore-to-stroke ratio. A two-valve per cylinder engine is also considered. Temporal evolutions of 0D-and 3D-derived mean flow velocity, turbulent intensity, and tumble velocity present very good agreements for each investigated engine geometry and operating condition. The model, particularly, exhibits the capability to accurately predict the tumble trends by varying some geometrical parameter of the engine, which is helpful to estimate the related impact on the burning rate. Summarizing, the developed 0D model well estimates the in-cylinder turbulence characteristics, without requiring any tuning constants adjustment with engine speed and valve strategy. In addition, it demonstrates the capability to properly take into account the intake duct orientation and the compression ratio without tuning adjustments. Some minor tuning variation allows predicting the effects of bore-to-stroke ratio, as well. Finally, the model is verified to furnish good agreements also for a two-valve per cylinder engine, and with reference to two different high-performance engines.

This study presents an experimental investigation of the novel combination of a "wave" bowl piston with thermal barrier coatings (TBCs) and Miller cycle intake valve strategies. All experiments were carried out with a single cylinder research engine with fully-flexible valve timing capabilities. The results indicate the wave bowl geometry enables this combination to improve fuel consumption, steady-state engine-out NOₓ emissions, and particulate matter (PM) emissions, improving the NOₓ-PM tradeoff that compromises diesel engine efficiency. These benefits were achieved at the expense of elevated turbocharger efficiency requirements. Three TBCs of varying composition and thickness were tested at seven operating conditions of varying speed and load. TBC performance was highly dependent on volumetric efficiency (VE), as cases with reduced VE increased the heat transfer gradient between the combustion gasses and the combustion chamber. The insulative properties of each TBC dete...

Experimental and numerical analyses of a turbocharged VVA SI engine. • 3D in-cylinder turbulence analyses for various valve strategies and engine speeds. • Validation of a 1D engine model, including sub-models of in-cylinder processes. • Effect of EIVC and LIVC strategies on fuel consumption in two operating points. • A methodology capable to support the virtual calibration of a VVA engine.

Engine manufacturers generally use aftertreatment systems to meet the strict emission criteria on automotive diesel engines. However, those systems operate inefficiently particularly at low-loaded cases of diesel engines since exhaust gas temperatures at aftertreatment inlet remain below 250 o C. For those cases, variable valve timing (VVT) method can be applied to elevate exhaust temperatures and improve aftertreatment emission conversion efficiency. Therefore, in this study, intake valve closing (IVC) timing is advanced and retarded sufficiently from the base condition on a low-loaded diesel engine to increase aftertreatment inlet exhaust temperature above 250 o C.. A specially designed computer program, Lotus Engine Simulation (LES), is utilized to model the diesel engine. Experimental data of a similar study is used for the validation of the simulation. Engine loading (taken as brake mean effective pressure (BMEP)) is kept constant at 2.5 bar by adjusting the fuel injection rate. The results show that there is a considerable exhaust temperature rise (up to 65 o C) at aftertreatment inlet with the method and it is adequate for effective aftertreatment performance (T exhaust > 250 o C). It is also seen that the increase on exhaust temperature is due to the sudden reduction on volumetric efficiency (from 94 % to 65 %). Therefore, there is lower air induction into the cylinders and hence lower pumping losses which result in fuel-efficiency in the system. However, air flow reduction also causes a sharp decrease on the exhaust flow rate which affects the heat capacity of exhaust gases negatively in the system.

In order to mitigate the greenhouse gases emission from automobiles and to reduce the dependency on fossil fuels, various alternatives for replacing the internal combustion engine are available. However, the best solution for this dilemma must take into account the geographic and social-economic characteristics of the country, its energy matrix, its emission legislation, and the fuel carbon footprint during its entire lifecycle. Brazil has a strong reputation for its fleet of Flex-Fuel vehicles, long date experience in the use of ethanol fuel and its distribution network. This differentiates it from other global markets and justifies a unique approach for the CO2 emission reduction. This article describes a project with the main objective of optimizing the efficiency of Flex-Fuel engines running on ethanol, without deteriorating their performance with gasoline. The influence of the geometric compression ratio, the airflow structure and the inlet valve opening/closing strategy was investigated for fuel consumption and engine performance. The analysis of the experimental data confirmed the benefits of the compression ratio optimization on the combustion efficiency. Therefore, the development of efficient Flex-Fuel engines will lead to a sustainable route for mobility in Brazil.

Variable Compression Ratio (VCR) engine is seen as one of the next improvements of Spark Ignition (SI) engines. Regarding at the robustness of fuel consumption improvement of a technology though different Driving Cycles (NEDC, WLTC, Artemis, FTP, Real Driving Cycle…), the association of Variable Compression Ratio (VCR) engine with simple mechanical Variable Valve Actuation (VVA) is a promising solution for a "right sized" engine compared to highly downsized engines.

Different technologies are being utilized nowadays aiming to boost the fuel efficiency of Spark-Ignition (SI) engines. Two promising technologies which are used to improve the part load efficiency of SI engines are the utilization of downsizing in combination with turbocharging and cylinder deactivation. Both technologies allow a shift of load points towards higher loads and therefore towards more efficient zones of the engine map, while performance is being preserved or even enhanced despite the smaller displacement thanks to high boost levels. However, utilization of both technologies will increase the risk of knock dramatically. Therefore, the abovementioned systems can be coupled with other technologies such as gasoline direct injection, Miller cycle and water injection to mitigate knock at higher load operating conditions. Therefore, the aim of the current work is to investigate, through experimental and numerical analysis, the potential benefits of different knock mitigation t...

Though there are multiple viable powertrain options available for the automotive sector, those that contain internal combustion engines will continue to account for the majority of global sales for the next several decades. It is therefore imperative to continue the pursuit of novel combustion concepts that produce efficiency levels significantly higher than those of current engines. Introducing high levels of dilution in spark ignited (SI) engines has consistently proven to produce an efficiency benefit compared to conventional stoichiometric engine operation. However, this combustion mode can present challenges for the ignition system. Pre-chamber jet ignition enables stable, highly dilute combustion by both increasing the ignition energy present in the system and distributing it throughout the combustion chamber. Previous work by the authors have shown that jet ignition produces 15–25% increases in thermal efficiency over baseline SI engines with only relatively minor changes to ...

The main aim of the research was to investigate influence of overlap of the natural gas fuelled spark ignited engine on the following parameters: Indicated Mean Effective Pressure (IMEP), heat rate release including combustion phases (ignition lag, main combustion phase). The content of the study includes results from processing in-cylinder pressure measurements, heat release rate analysis, combustion phases, and finally the conclusions. The tests were carried out on the test bed including the single cylinder research engine with a displacement volume of 550 cm3. The engine was equipped with independent cam phasors for both intake and exhaust valves, but for this investigation, the exhaust valve timing was fixed (the exhaust cam centre line was fixed at -95 crank angle (CA) deg before Top Dead Centre) and intake valve timing was changed (the intake cam centre line was varied from 90 to 150 CA deg after Top Dead Centre). The overlap was changed in the range from 85 to 25 CA deg. 8 te...

New legislation involving emissions from internal combustion engines are pushing the manu-facturers to develop new technology faster than ever before with the amount of greenhouse gases. To meet the standards new concepts need to be developed with lower fuel consumption and emissions. This thesis covers the implementation of a couple of methods to achieve this. These concepts are DEP with fully variable valves in a port fuel SI engine with high compres-sion ratio (CR). The results show an increase in efficiency followed by lowered fuel consump-tion. The improvements in fuel consumption are mainly found to be the result of raising the CR and because of decreases in pumping losses due to de-throttling via the Miller-cycle. The reduction in pumping losses by implementing the DEP concept was not as great as expected. The results show a decrease of fuel consumption of 9.5% at part load and 5 % at high load. The main improvement with the DEP concept was the reduction of the in-cylinder re...

DESCRIPTION Atkinson cycle is already recognized for having a better thermal efficiency then Otto cycle. That cycle is used so far mostly on reciprocating internal combustion engines (ICE) by changing the configuration of crank mechanisms. Miller cycle simulates Atkinson cycle by late closing of intake valves on ICE with classical (symmetrical) crank mechanisms. Rotary engines presents several advantages over conventional reciprocating ICE while having, in general, no valves or crankshafts. In this paper, the use of Atkinson / Miller cycle on a valveless rotary engine is proposed. The results highlight the rise on thermal efficiency while keeping inherent advantages of rotary engines.

Gasoline engine downsizing has become a popular and effective approach to reduce CO 2 emissions from passenger cars. This is typically achieved in the form of a boosted direct injection gasoline engine, which are typically equipped with variable valve timing (VVT) devices on the intake and/or exhaust valves. This paper describes the synergies between valve timings and boost based on experimental investigations in a single cylinder gasoline direct injection spark ignited (DISI) engine with variable cam phasing on both the intake and exhaust cams. Two cam profiles have been tested to realize Miller cycle and compared with the standard camshaft. One cam features a long opening duration and standard valve lift for Late Intake Valve Closing (LIVC) and the other cam has a short opening duration and low valve lift for Early Intake Valve Closing (EIVC). An external boost rig was used to provide adjustable pressurized air charge, allowing conditions of up to 4000rpm and 25.6 bar NIMEP to be studied.

Energy independence and reduction in pollutant emissions are a center of interest for several researchers and car manufacturers Renewable fuels have gained in popularity because of their sustainability and, in some cases, lower amounts of greenhouse Moreover, energy diversification is also required by all countries One possible solution is the use of biofuels such as ethanol, methanol, etc. These biofuels have been shown as good candidates as alternative fuels for vehicles because they are liquid several physical and combustion properties similar to gasoline. Alcohols have also a higher octane number and oxygen content gasoline. This allows the alcohol engines to have much higher compression ratios (CRs), and thus, better BTE (br efficiency). Brazilian car manufacturing industry has developed flexible-fuel vehicles, introduced in 2003, which became a commercial success. Flex fuel internal combustion engines (ICEs) can run on any proportion of Brazilian gasoline (E27 blend) and hydrous ethanol (E100), allowing the use of the cheaper fuel available. However, conventional flex fuel engines have a fixed CR, generally between the ideals CRs for gasoline and ethanol, which leads to lower BTE and higher fuel consumption. In order to reduce or eliminate these issues, this paper presents the Kopelrot engine, a flexible fuel rotary engine with dynamically variable compression ratio.

Energy independence and reduction in pollutant emissions are a center of interest for several researchers and car manufacturers Renewable fuels have gained in popularity becau sustainability and, in some cases, lower amounts of greenhouses gases. Moreover, energy diversification is also required by all countries. One possible solution is the use of biofuels such as ethanol, methanol, etc. These biofuels have been shown as good candidates as alternative fuels for vehicles because they are liquid several physical and combustion properties similar to gasoline. Alcohols have also a higher octane number and oxygen content gasoline. This allows the alcohol engines to have much higher compression ratios (CRs), and thus, better BTE (br efficiency). Brazilian car manufacturing industry has developed flexible-fuel vehicles, introduced in 2003, which became a commercial success. Flex fuel internal combustion engines (ICEs) can run on any proportion of Brazilian gasoline (E27 blend) and hydrous ethanol (E100), allowing the use of the cheaper fuel available. However, conventional flex fuel engines have a fixed CR, generally between the ideals CRs for gasoline and ethanol, which leads to lower BTE and higher fuel consumption. In order to reduce or eliminate these issues, this paper presents the Kopelrot engine, a flexible fuel rotary engine with dynamically variable compression ratio.

Atkinson cycle is already recognized for having a better thermal efficiency then Otto cycle. That cycle is used so far mostly on reciprocating internal combustion engines (ICE) by changing the configuration of crank mechanisms. Miller cycle simulates Atkinson cycle by late closing of intake valves on ICE with classical (symmetrical) crank mechanisms. Rotary engines presents several advantages over conventional reciprocating ICE while having, in general, no valves or crankshafts. In this paper, the use of Atkinson / Miller cycle on a valveless rotary engine is proposed. The results highlight the rise on thermal efficiency while keeping inherent advantages of rotary engines.