Miller Cycle Research Articles

Influence of variable enhanced LIVC miller cycle coupled with high compression ratio on the performance and combustion of a supercharged spark ignition engine

A novel variable enhanced late intake valve closing (LIVC) Miller cycle with asynchronous valve opening was proposed. Relevant tests were carried out in a supercharged spark ignition (SI) engine with high compression ratio, which mainly included the effects of variable valve timing on performance and combustion characteristics, as well as the comparison with the baseline engine. The purpose of this study was to explore the effect of different intake and exhaust opening timing on the performance and combustion characteristics of the enhanced LIVC Miller cycle with asynchronous valve opening, and further explore the energy saving potential of this Miller cycle. The results showed that the application of variable enhanced Miller cycle effectively improved the anti-knock ability and pumping loss of the engine with high compression ratio. On the one hand, the optimization of pumping loss substantially improved the fuel economy under small load conditions. On the other hand, better combustion performance and air-fuel ratio could be achieved at medium and high loads. Meanwhile, the exhaust valve should be opened as earlier as possible to achieve the best fuel economy. Correspondingly, under optimal valve timing, compared with the baseline engine, the asynchronous intake valve opening variable enhanced Miller cycle engine with high compression ratio had a fuel economy optimization of more than 3.5 % under all loads, and the maximum fuel economy optimization was 12.74 % under the condition of 11 bar.

Experimental Study on the Combustion and Emission Characteristics of Methanol/Gasoline Fuels in Direct Injection Miller Cycle Gasoline Engines

Experimental Study on the Combustion and Emission Characteristics of Methanol/Gasoline Fuels in Direct Injection Miller Cycle Gasoline Engines

Investigation on varied sewage sludge producer gas and methane blend equivalence ratios operated SI engine intact with Miller cycle strategy

Decentralised power generation through a gasifier-engine genset can reduce both reliance on power grid and pollution. However, the low calorific value of the produced gaseous fuel moderates engine power and efficiency, which is a big challenge for its utilisation. For early and cost-effective solution prediction, a simulation tool of adequate precision can effectively envisage dual-fuel (DF) mode engine performance. Thus, this study simulates DF-SI engines with late inlet valve closures (LIVCs) to improve thermal efficiency using the Miller cycle strategy. Simulation is performed using quasi-dimensional thermodynamic modelling (QDTM). After validating the model using referred experimental results, QDTM was employed to study the parametric impacts of inputs (blends, LIVC and equivalence ratio) variations on performance and emissions response parameters. Power improves by blending sewage sludge-based producer gas with methane. Multi-objective optimisation through the response surface method (RSM) determined the optimum operating parameters as 0.814 equivalence ratio, 68.23% SSPG-blend and 55.9° CA (ABDC) LIVC. Corresponding optimal responses were 5.906 bar IMEP, 3.85 kW BP, 28.6% BTE, 12.596 MJ/kWh BSEC, 0.134 V% CO and 2045.29 ppm NO emissions. ANOVA-based optimal results presented a composite desirability of 0.843 with a 95% confidence level. Conclusively, methane mix and LIVC approach increase the power and efficiency of the DF-SI engine; additionally, optimisation guides to balance power and emission trade-off.

Performance analysis of methanol fuelled SI engine with boosted intake pressure and LIVC: A thermodynamic simulation and optimization approach

Methanol (CH3OH) is a low-carbon alternative fuel that can be derived through renewable power-to-fuel conversion, offering lower emissions and a higher resistance to knock in SI engines. However, the sole methanol-powered SI engine delivers less brake power. Fuels with a higher calorific value have been blended to solve this problem. However, this may cause overburden with storage, handling, and correct blending (like when methane and hydrogen are blended). To resolve this, this research suggested a novel approach for increasing the power and efficiency of a SI engine using the LIVC (late inlet valve closing) miller cycle and boosted intake pressure under 14 geometrical compression ratio (GCR) with the addition of the start of spark timing (SOI) and equivalency ratio (λ) effects. A quasi-dimensional thermodynamic model (QTDM) was applied to simulate the engine performance with respect to operating variables of 0.6–1.0 λ, 35.50 ––650 aBDC (after Bottom Dead Centre) LIVC timing, 30.00 ––150 bTDC (before Top Dead Centre) SOI Timing and 0.8–1.5 bar intake pressure. After that, design of experiments (DoE) based response surface methodology (RSM) was applied to determine optimum operating setting to maximize power and efficiency and minimize emission and fuel consumption. The results from the RSM illustrate the optimum input parameters to be 0.793 equivalence ratio, 46.900 aBDC-LIVC, 20.750 bTDC-SOI timing, and 1.5 bar intake pressure. Correspondingly, response output performances were found to be 12.36 kW-indicated power (IP), 11.20 kW- brake power (BP), 43.32 % indicated thermal efficiency (ITE), 39.32 % brake thermal efficiency (BTE), 9150.6 kJ/kWh brake specific energy consumption (BSEC), and 0.3 V%- carbon mono oxide (CO), 1247.8 ppm-nitric oxide (NO) emission at exhaust valve opening (EVO). The ANOVA regression models resulted in 95 % accuracy in forecasting output response and composite desirability of optimization of 0.83. Overall, it was found that miller-based LIVC and boosted intake pressure considerably improve the performance of SI engines, and the results projected would be helpful for further study and industry application.

Applications of Oxyhydrogen, Direct Water Injection, and Early-Intake Valve Closure Technologies on a Petrol Spark Ignition Engine—A Path towards Zero-Emission Hydrogen Internal Combustion Engines

This study investigates the performance of a 4-MIX engine utilizing hydrogen combustion in pure oxygen, water injection, and the application of the early-intake valve closure (EIVC) Miller cycle. Transitioning from a standard petrol–oil mix to hydrogen fuel with pure oxygen combustion aims to reduce emissions. Performance comparisons between baseline and oxyhydrogen engines showed proportional growth in the energy input rate with increasing rotational speed. The oxyhydrogen engine exhibited smoother reductions in brake torque and thermal efficiency as rotational speed increased compared to the baseline, attributed to hydrogen’s higher heating value. Water injection targeted cylinder and exhaust temperature reduction while maintaining a consistent injected mass. The results indicated a threshold of around 2.5 kg/h for the optimal water injection rate, beyond which positive effects on engine performance emerged. Investigation into the EIVC Miller cycle revealed improvements in brake torque, thermal efficiency, and brake specific fuel consumption as early-intake valve closure increased. Overall, the EIVC model exhibited superior energy efficiency, torque output, and thermal efficiency compared to alternative models, effectively addressing emissions and cylinder temperature concerns.

Experimental study on the impact of Miller cycle coupled EGR on a natural gas engine

The Miller cycle has significant advantages of suppressing knocking and improving nitrogen oxide (NOX) emissions without the penalties of reducing engine fuel consumption and power output. In the study, the effect of non-Miller cycle and Miller cycle on the exhaust gas recirculation (EGR) introduction capability and the knocking boundary were evaluated on a stoichiometric combustion natural gas engine at three different loads. Additionally, the effect of Miller cycle coupled EGR and ignition timing on engine performance and combustion process was discussed. The results indicate that, for the same condition, the Miller cycle could reduce peak temperature and pressure, increased combustion duration, and delayed combustion phase, which makes for effective knocking suppression. Therefore, the Miller cycle has less dependence on the EGR strategy to control knock. Moreover, the Miller cycle can also reduce the ability to introduce EGR, which could up to 3.8%. By matching the ignition timing and EGR rate, the BSFC of the Miller cycle were decreased by 0.6g/kW·h, 2.4 g/kW·h and 2.9 g/kW·h respectively for three test conditions compared with non-Miller cycle. In terms of emissions, the Miller cycle and EGR can both suppress NOX emissions, while the EGR being more effective. The study will provide valid information for the application of the Miller cycle to achieve efficiency clean combustion of natural gas engine.

Effects of the turbocharged Miller cycle strategy on the performance improvement and emission characteristics of diesel engines

The turbocharged Miller cycle strategy is studied to improve the power density of diesel engines and reduce emissions. A thermodynamic model and a 1D simulation model of turbocharged diesel engine are established. Results show that the introduction of the Miller cycle reduces the thermal efficiency under naturally aspirated conditions because of the low effective compression ratio, whereas it increases the thermal efficiency under a turbocharged condition owing to the energy recovered by the turbocharger. Under restricted combustion pressure and fixed intake mass, the thermal efficiency first increases and then decreases with increasing Miller cycle ratio, and the peaks occur at approximately 30%–50%. The gain of isochoric combustion ratio overlaps the loss of effective compression ratio due to the Miller cycle on the lower side, whereas it reverses on the higher side. With maximum and equal intake mass, the maximum power initially increases and subsequently decreases with increasing Miller cycle ratio, reaching a peak at 40%. Under a fixed isochoric combustion ratio, the thermal efficiency first increases and then decreases with increasing intake mass, and the optimum intake mass corresponding to the highest thermal efficiency decreases with increasing Miller cycle ratio. The lower the restricted combustion pressure is, the higher the gain in power and thermal efficiency by the Miller cycle strategy. Based on the calculation of the 1D model validated using a practical engine, the power can be increased from 41.6 kW/L to 100 kW/L while the brake thermal efficiency can be increased from 34.98% into 38.55% by increasing the Miller cycle ratio from 19% to 30% and the combustion pressure from 17.7 MPa to 35 MPa. With the application of the supercharged Miller cycle, when the Miller cycle ratio is 30% and the power intensity is increased from 60 kW/L to 100 kW/L, NOx decreases by 32.4%, CO decreases by 28%, showing a tendency to decrease and then stabilize, and HC increases by 5.3%. When the power is 80 kW/L and the Miller cycle ratio is increased from 10% to 30%, NOx decreases by 8.6%, CO decreases by 2%, and HC increases by 0.04%.

Study on methanol-hydrogen engine in extended-range electric vehicles

The demand for clean and efficient new vehicle models is steadily increasing. Methanol-hydrogen engines use methanol as the main fuel and can recover the heat from engine exhaust to dissociate part of methanol into hydrogen-rich syngas. The syngas is recirculated back into the engine cylinder to improve combustion. Therefore, methanol-hydrogen engines have a higher energy utilization efficiency. This paper designed a methanol-hydrogen engine system based on a Miller cycle methanol engine. Bench tests showed that combusting methanol and dissociated methanol gas together could accelerate the fuel burn rate and improve the engine’s fuel economy. At a fixed engine speed of 2500 r/min, the BSFC of the methanol-hydrogen engine was reduced up to 5.55% compared to the original methanol engine. Further, a methanol-hydrogen extended-range electric vehicle powertrain model was built in Simulink. Simulation results indicated that, under the WTLC cycle, the methanol-hydrogen engine achieved a 22.60% reduction in fuel consumption per 100 km and saved 58.89% in fuel costs compared to the conventional gasoline engine. The methanol-hydrogen engine presented potential application in the extended-range electric vehicle.

A Study of the Effect of the Miller Cycle on the Combustion of a Supercharged Marine Diesel Engine

A Study of the Effect of the Miller Cycle on the Combustion of a Supercharged Marine Diesel Engine

Effects of asynchronous late intake valve closing combined with high geometric compression ratio and exhaust gas recirculation on combustion and fuel consumption in a turbocharged SI engine:An experimental study

To achieve low-carbon transportation, a novel Miller cycle was implemented by using asynchronous late intake valve closing (ALIVC) in the high compression ratio turbocharged SI engine. The effects of the Miller cycle on combustion and performance were investigated and compared with the original Otto cycle. Based on this, EGR was introduced and its effects on Miller cycle engine performance and energy balance were investigated. The results show that the Miller-CR12.5 can reduce pumping loss and suppress knock without sacrificing power output. Compared to the Otto-CR10.5, the Miller-CR12.5 achieves a 6.7 % reduction in BSFC at the lowest fuel consumption point and a 10–11.4 % reduction at high loads. The lower peak combustion temperature allows the Miller-CR12.5 to eliminate fuel-enriched injection at high loads, reducing the heat transfer and combustion loss. The introduction of EGR in the ALIVC Miller cycle engine decreases the peak HRR and extends the combustion duration. However, the advanced 50 % combustion position and increased effective expansion ratio can improve engine performance. At 10 % EGR rate, the BSFC obtains a 2.1 % reduction and NOx emissions are reduced by 62 %. As the EGR rate increases, the heat transfer and exhaust loss decrease, but there is a slight increase in combustion loss.

A comprehensive experimental study to analyze the cyclic variation of a hydrogen-blended ammonia engine with the Miller cycle

The effects of multiple operating parameters (including speed, valve timing, λ, manifold absolute pressure, spark timing, and hydrogen injection timing) on the coefficient of variation of indicated mean effective pressure (CoVIMEP) of a hydrogen-blended ammonia engine have not been adequately evaluated, which motivates this study. Specifically, CoVIMEP is decreased from exceeding 2.4 % to approximately 0.7 % when the speed increases from 1300 rpm to 2000 rpm. Optimizing valve timing keeps CoVIMEP below 0.8 % by improving the airflow exchange process, and the engine tends to realize lower CoVIMEP at close stoichiometric ratio conditions and low pumping loss. Furthermore, adjusting spark timing affects CoVIMEP by varying the ignition process's stability, with a combustion center of gravity around 9°CA ATDC being suggested. The hydrogen direct-injection timing influences the combustion process's instability by varying the mixture concentration gradient, and the late injection strategy allows the engine to achieve a CoVIMEP of less than 0.9 %.

Power and efficiency improvement of SI engine fueled with boosted producer gas-methane blends and LIVC-miller cycle strategy: Thermodynamic and optimization studies

An appealing alternative solution for lowering both reliance on power grid and pollution is by adopting decentralized power generation using gasifier-engine integrated systems. However, the utilization of gasification-derived producer gas (PG) leads to low engine power output and efficiency as compared to conventional fuels. This pertains to its low Calorific value(CV) and low flame-speed. Therefore, this simulation study aims to simulate and investigate the improvements in these parameters by inspecting various boosted-intake pressures and blends of high-CV methane with PG as inputs along with the implementation of Late inlet valve close(LIVC)-Miller cycle strategy on a 1500 RPM Dual-fuel(DF) SI engine model. Quasi-dimensional thermodynamic modelling (QDTM) was applied to simulate this performance and emission investigation by considering Sewage sludge-based PG (SSPG) as the PG variant. Best operational input settings were found using the Response Surface Methodology(RSM)-based multi-objective optimization. These optimal inputs were 3 bars of Pressure at intake valve closure (PIVC), 76.94 % SSPG-blend, and 77.32⁰ (ABDC) LIVC. The responses were correspondingly predicted as 40.46 % ITE, 21.35 bars IMEP, 16.8 kW BP, 20.04 bars BMEP, 9.48 MJ/kWh BSEC, with 0.08 V% CO and 3094 ppm NO emissions. Finally, with the ANOVA-based analysis, a 0.712 composite desirability was achieved with 95 % confidence level.

Efficiency improvement investigation through Miller cycle strategy for SI engine operating on stoichiometric producer gas and methane blends

Decentralized power generation through gasifier-engine system is an attractive alternative for reducing environmental impact and power grid dependency. For effective sewage sludge-waste to end-use electricity generation by engine integration, this work aims to simulate and investigate thermal efficiency enhancement in SI engine by employing late inlet valve close (LIVC) strategy with 12.0:1 geometrical compression ratio miller cycle and operating engine with sewage sludge-based producer gas (SSPG) by blending methane in various proportions. A quasi-dimensional thermodynamic model is simulated to explore SI engine performance, after validation from an experimental reference. Effects of blending SSPG to methane, varying LIVC and spark timing were analyzed respective to indicated thermal efficiency (ITE), indicated power (IP), brake thermal efficiency (BTE), brake power (BP), brake-specific energy consumption (BSEC) and emissions (CO and NO). Parametric results were found in trade-off nature of performance corresponding to engine efficiency and power. Thus, response surface methodology (RSM) was applied to find the best operating conditions for enhancing performance and diminishing emissions of the blended fuel SI engine. 64.7 % SSPG Blend, 70.33⁰ (ABDC) LIVC, and 34.03⁰ (BTDC) SOI were found as optimum operating parameters corresponding to the generated optimal responses of 35.47 % ITE, 5.18 kW IP, 27.95 % BTE, 4.08 kW BP, 12.671 MJ/kWh BSEC, and 0.688 V% CO, 1456.93 ppm NO emissions. The ANOVA-based regression model shows composite desirability of 0.8 with 95 % confidence level. In summary, the optimization method and optimal operation parameters offer significant reference for improving engine performance for high CR miller cycle-based LIVC approach.

Effect of flexible camshaft technology on dual-fuel engine performance using phenomenological combustion model

AbstractThe objective of the current study is to investigate the effect of tunable valve timings on the performance and emissions of a dual-fuel marine engine. A simulation model was developed in MATLAB to simulate the valvetrain mechanism. The model generates different valve lift curves depending on the input conditions, and after that, it tests them against any possible collision with the piston. The valid valve lift curves were exported to a two-zone combustion model in AVL CRUISE-M platform. The combustion model depends on the fractal principle and aims to predict the in-cylinder parameters. In addition, it contains sub-models to calculate the ignition delay and emissions formation. Model results were compared against experimental data, as the latter were obtained from a heavy-duty, medium-speed, single-cylinder research engine, which employs natural gas as a main fuel. The results showed good agreement and the model was used for further investigations with other cam pairs. It has been found that the fractal combustion model can effectively represent the combustion behavior in the dual-fuel engine. Furthermore, valve timing has a significant influence on the engine performance and exhaust emissions. Results also revealed that applying Miller cycle can reduce the nitrogen oxides emissions, while the higher valve overlap period had a negative effect on methane slip.

Power and efficiency optimizations of Maisotsenko-Atkinson, Dual and Miller cycles and performance comparisons with corresponding traditional cycles

Power and efficiency optimizations of Maisotsenko-Atkinson, Dual and Miller cycles and performance comparisons with corresponding traditional cycles

Investigation of Lips-Guided-Flow Combustion Chamber and Miller Cycle to Improve the Thermal Efficiency of a Highly Intensified Diesel Engine

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.

Effects of methanol direct injection and high compression ratio on improving the performances of a spark-ignition passenger car engine

The high octane number and high latent heat of vaporization of methanol are beneficial to suppress knock and consequently increase compression ratio (CR) of spark ignition engines, and thus improve the thermal efficiency. Few preious research on methanol engine combuston and performances have been conducted based on spark-ignition passenger car engines with a CR greater than 14. In this study, a 1.5-liter spark ignition passenger car engine with miller cycle was used to explore the potentials of high CR and methanol direct injection (MDI) on improving engine performances. First, the engine was tested under stoichiometric combustion using methanol and gasoline at BMEPs of 1.1 MPa and 1.5 MPa with CR11.5, CR13.8, and CR15.3. Then, the performances of the CR11.5 case with gasoline and the CR15.3 case with methanol were compared under lean burn combustion. The results show that for gasoline, increasing CR from 11.5 to 15.3 results in decreased fuel economy under stoichiometric combustion, whereas the exact opposite tendency is shown for methanol. Integrating a high CR of 15.3 and MDI improves brake thermal efficiency (BTE) to 43.3 % at an excess air/fuel ratio (λ) of 1.0, when compared with 37.4 % of gasoline at CR11.5. Applying lean burn can further improve the BTE of methanol at CR15.3 to 44.9 %. The main causes of the improvement of BTE by high CR and MDI are the reduced exhaust heat loss resulted from earlier combustion phasing. However, high CR and MDI also extend combustion durations at all specified λs, and emit more THC and CO emissions than low CR with gasoline at high λs because of higher surface/volume ratio and flame quenching. The extended combustion duration and the incomplete combustion are the main barriers to greater BTE for MDI sprak ignition engine with high CR.

Evaluation of thermal management technologies for fuel efficient cold-start emissions reduction in diesel engines

The ultra-low NOx emission limits for heavy and mid-duty vehicles, which are expected to be imposed in both Europe and the USA by 2027, together with the enforcement of continuous decrease in CO2 emission levels, make the need for adoption of newer technologies in the automotive industry imperative. To achieve low tailpipe NOx emissions, the accelerated warm-up of the exhaust aftertreatment system is of great importance. On the other hand, the thermal management strategies applied for this purpose result in fuel consumption penalty and consequently higher CO2 as it can be widely found in the literature. Thus, the use and optimization of advanced thermal management technologies is critical to decrease the NOx– fuel penalty trade-off on the basis of complete driving cycles. In the present work an integrated modeled-based approach is implemented by coupling advanced, predictive 1D engine, and aftertreatment simulation models which are extensively validated via dedicated experimental data. The main goal of this approach is to define and investigate multiple engine or aftertreatment-based thermal management technologies, as well as a combination of them, creating a more efficient warm-up mode for the engine. Thermal measures such as cylinder deactivation, retarded start of the main injection, late intake valve closing (Miller cycle), intake throttling, elevated idle speed, and secondary fuel injection upstream the DOC are evaluated for their effect on the exhaust system heat-up time, the fuel consumption penalty and more importantly, for their impact on the tailpipe NOx emissions calculated by this holistic simulation approach.

Gemi Dizel Motorunda Azot Oksitleri (NOx) İndirgeme Yöntemlerinin İncelenmesi

Reducing nitrogen oxide (NOx) emissions is of great importance in terms of environmental sustainability and air quality. This study is a review that examines various applications aimed at reducing NOx emissions. Below is a summary of the evaluation of technologies, including the common rail system, exhaust gas recirculation (EGR), Miller cycle, direct water injection, emulsified fuel, and selective catalytic reduction (SCR). The common rail system, EGR, and Miller cycle can generally be considered as combustion control-based methods for reducing NOx within the cylinder. Direct water injection and emulsified fuel aim to lower temperatures inside the cylinder by utilizing the high internal heat of evaporation of water. Selective catalytic reduction is a technology where NOx in the exhaust gas is converted into nitrogen gas and water vapor through the use of a catalyst. This study evaluates the effectiveness and applicability of various technologies used to reduce NOx emissions. Each method may have different advantages and disadvantages. Additionally, there may be certain limitations and variations depending on the application areas of these methods. Therefore, a careful assessment is necessary to determine the most suitable technology or combination of technologies for reducing NOx emissions.

Investigation on the performance of a by-product hydrogen-fueled spark-ignition engine with Miller cycle under various lean conditions

The direct combustion of by-product hydrogen is a promising way for reducing costs and greenhouse emissions. Coke oven gas (COG) which is mainly composed of H2, CH4 and CO is a major source of by-product hydrogen that is suitable to be adopted by internal combustion engines. This paper investigated the COG combustion in a spark-ignition engine with Miller cycle. To get an overview of by-product hydrogen combustion properties, two kinds of COG compositions with the maximum and minimum hydrogen fractions were tested. The excess air ratio (λ) was raised from stoichiometric to the lean limit to explore the capability of COG on improving the engine performance under a common-driving speed of 1500 rpm and part load conditions. The test results indicated that the engine fueled by COG with higher hydrogen fractions could gain concentrated heat release period, extended lean burn limit, reduced HC and CO2 emissions, and enhanced working capability only at ultra-lean conditions. The properly increased λ availed improving engine efficiency and lowering HC emissions. The peak indicated thermal efficiency of 38.6% was acquired at the λ of 1.2, while the lowest HC emissions of only 32 ppm was gained at the λ of 1.4. Under ultra lean conditions, NO emission dropped to near zero, and CO from the by-product hydrogen-fueled engine was negligible for all tested ranges. An interesting trend of peak pressure correlated crank angle versus λ was also found in this study.