Exhaust Valve Opening Timing Research Articles

Study on the Effect of Parameter Sensitivity on Engine Optimization Results

The effects of six control parameters, intake valve opening timing (IVO), exhaust valve opening timing (EVO), compression ratio (CR), engine speed, intake temperature, and intake pressure on engine output power, indicated specific fuel consumption (ISFC), and nitrogen oxides (NOx) emissions, are analyzed through engine simulation. The six parameters were categorized into two groups based on the degree of influence: high influence (EVO, speed and intake pressure) and low influence (CR, IVO and intake temperature). The relationship between these two groups of parameters and power, ISFC and NOx emissions was explored. Optimization was carried out for each of the two groups of parameters, and the optimization of the high impact parameters resulted in a higher diversity and wider distribution of the solution set. On the other hand, the optimization of the low-impact parameters resulted in a more concentrated distribution of the solution set, while better reflecting the trade-off between the optimization objectives. For the optimal solutions for both sets of parameters, the high-impact parameters provided significant optimization performance compared to the standard operating conditions. Although power and ISFC were optimized, the optimal solution for the low-impact parameter performed poorly with a significant increase in NOx emissions. Therefore, the parameters should be evaluated for optimization using high impact parameters to improve engine performance.

Investigation of the control strategy for hydrogen addition in all operating conditions of a high compression ratio liquid methane heavy-duty engine

The hydrogen addition to liquid methane gas (LMG) engines based on the rational control strategy is considered to be a promising approach to improve the performance of LMG engines. However, the current studies are limited to a few operating points. To comprehensively develop a control strategy of hydrogen addition for high compression ratio LMG engines, the effects of hydrogen addition on the emissions, combustion, and performance of an LMG engine are experimentally investigated under all operating conditions in this study. Furthermore, to achieve the optimal performance of the hydrogen-LMG engine with the optimal hydrogen blending, the coupled simulation model of MATLAB/Simulink and GT-Power is established based on the test bench, and the multiple operating parameters of the calibrated numerical model are optimized by using genetic algorithm. The results show that the maximum increases in the brake thermal efficiency with increasing hydrogen energy share (HES) are 1.6, 0.9 and 0.6 percentage points under low, medium and high loads, respectively. Correspondingly, the maximum reduction in EBSFC under low, medium and high loads is 6.5 %, 2.2 % and 1.4 %, respectively. The ignition delay is reduced and the combustion is promoted with the increase in HES. As a result, the cylinder pressure and HRR rise faster and reach a higher peak earlier. In addition, the 50 % combustion location is advanced and the 10–90 % combustion duration is shortened. In terms of emissions, the increasing HES promotes the NOx emissions and reduces the HC emissions. Especially at medium and high loads, the NOx emissions rise sharply with increasing HES. It is desirable that HES should not exceed 15 %, 4 % and 2 % at low, medium and high loads, respectively. In addition, by co-optimizing the intake valve opening timing, exhaust valve opening timing and the spark angle, the BSFC of the hydrogen-LMG engine with the optimal HES under 1200 rpm and BMEP of 6 bar is still improved by 2.2 %. This study provides new insights to further explore the energy-saving potential of hydrogen-LMG engines.

Assessment of a synergistic control of intake and exhaust VVT for airflow exchange, combustion, and emissions in a DI hydrogen engine

Variable valve timing (VVT) and Miller cycle are advanced technologies employed to optimize engine performance by improving airflow exchange, which are seldom investigated based on the direct-injection (DI) hydrogen engine. The objective of this study is to assess the effects of intake valve closing (IVC) and exhaust valve opening (EVO) timing on the gas exchange performance, combustion, and emissions of a DI hydrogen engine, after which a synergistic control strategy of IVC and EVO timing is proposed. This work is conducted under wide-open throttle and 1500 rpm. The results indicate that the synergistic control of IVC and EVO timing can increase volumetric efficiency by more than 40%, enhance gas exchange performance, shorten combustion duration, and reduce cyclic variation, resulting in approximately 43.15% brake thermal efficiency. Furthermore, brake mean effective pressure can be increased by more than 60% and NO emissions are controlled to less than 20 ppm by optimizing valve timings.

Development of a Zero-Dimensional Model for a Low-Speed Two-Stroke Marine Diesel Engine with Exhaust Gas Bypass and Performance Evaluation

Most large commercial vessels are propelled by low-speed two-stroke diesel engines due to their fuel economy and reliability. With increasing international concern about emissions and the rise in oil prices, improvements in engine efficiency are urgently needed. In the present work, a zero-dimensional model for a low-speed two-stroke diesel engine is developed that considers the exhaust gas bypass and geometry structures for the gas exchange model. The model was applied to a low-speed two-stroke 7G80 ME-C9 marine diesel engine and validated with engine shop test data, which consisted of the main engine performance parameters and cylinder pressure diagrams at different loads. The simulation results were in good agreement with the experimental data. Thus, the model has the ability to predict engine performance with good accuracy. After model validation, the variations in compression ratio, fuel injection timing, exhaust gas bypass valve opening portion, exhaust valve opening timing, and exhaust valve closing timing effects on engine performance were tested. Finally, the influence level of different parameters on engine performance was summarized, which can be used as a reference to determine the reasons for high fuel consumption in some cases. The developed engine performance model is considerable in digital twins for performance simulation, health management, and optimization.

Evaluation of the variable valve timing strategy in a direct-injection hydrogen engine with the Miller cycle under lean conditions

The favorable physicochemical characteristics of hydrogen make it an excellent alternative fuel for IC engines. Compared with hydrogen port injection, hydrogen direct injection provides multiple degrees of freedom for injection strategies and mixture formation, which can effectively suppress abnormal combustion and enhance engine performance. Variable valve timing (VVT) and the Miller cycle, as advanced and effective means of improving engine performance, are less investigated based on a direct-injection (DI) hydrogen engine. Hence, to optimize the performance of a DI hydrogen engine, strategies of the Miller cycle and VVT are introduced. In this work, a 1.5 L direct-injection engine with a VVT system was employed to evaluate the effects of the Miller cycle, intake valve closing (IVC) timing, and exhaust valve opening (EVO) timing on the airflow exchange process, in-cylinder charge characteristics, heat release process, dynamics and emission characteristics. The engine speed was stabilized at 1400 rpm and the strategies of lean combustion and late injection were used. The main results are as follows. As the IVC timing is delayed, the ratio of pumping mean effective pressure to indicated mean effective pressure (PMEP/IMEP) first decreases and then slightly increases, and the engine tends to achieve a high level of brake thermal efficiency (BTE) when PMEP/IMEP is lower. The optimization of intake and exhaust VVT can shorten combustion duration and reduce cyclic variation by increasing volumetric efficiency and improving mixture distribution at ignition timing. Furthermore, the engine reaches 42.22% BTE and a high level of brake mean effective pressure by the cooperative control of IVC and EVO timing. NOx emissions can be controlled below 100 ppm by employing the synergistic effect of the Miller cycle and VVT. It is worth mentioning that exhaust VVT as a way to compensate for the performance of the DI hydrogen engine with the Miller cycle should not be ignored.

Experimental approach for reducing nitrogen oxides emissions from ammonia–natural gas dual-fuel spark-ignition engine

In this study, characteristics of nitrogen oxides (NOx) emissions from an ammonia–natural gas dual-fuel operation were investigated by conducting spark-ignition engine experiments under the maximum load and a low engine speed (∼1,100 rpm). The feasibility of using a conventional selective catalytic reduction (SCR) system to reduce the NOx emissions was also investigated. For the experiments, an 11-L six-cylinder spark-ignition engine was used with appropriate modifications to use natural gas and ammonia together as the fuel. Several species comprising NOx emissions (NO, NO2, and N2O) and ammonia were measured together using a Fourier transform infrared analyzer (FT-IR). An aftertreatment system, including an SCR system and an ammonia oxidation catalyst (AOC), for an original natural gas-fueled engine was used to reduce engine-out NOx using the unburned ammonia as a reducing agent.From the experimental results, it was found that the NO concentration first increased on the addition of ammonia, as the fuel NOx emissions were produced. However, the total NO concentration became saturated with increasing ammonia fraction, owing to the increased amount of unburned ammonia. Specifically, considering the trend of the burned gas temperature and its value at exhaust valve opening (EVO) timing, it is inferred that nitrogen oxide was reduced owing to unburned ammonia after the exhaust valve opening timing, where the temperature range of combustion product was suitable to trigger selective non-catalytic reduction (SNCR). The remaining ammonia, after the SNCR, was then virtually oxidized to reduce the remaining NO while passing SCR system, showing an almost zero level (<10 ppm) at the catalyst-out level. N2O and NO2 were produced in the order of tens and hundreds of ppm, respectively. Thus, despite the high level of global warming potential (GWP) of N2O, its contribution to global warming effect was not significant. On the other hand, the unburned methane was particularly increased at some point with poor combustion efficiency to offset the effect of decrement in carbon dioxide due to its high level of GWP.

Computational exploration of single-fuel reactivity controlled compression ignition engine by integrating dimethyl ether/steam on-board reforming

A single-fuel dimethyl ether reactivity-controlled compression ignition engine system was established by integrating dimethyl ether/steam on-board reforming. For the dimethyl ether reforming reactivity-controlled compression ignition engine system, the product of dimethyl ether reforming (including the generated syngas and unreacted dimethyl ether) was provided through the intake port of the reactivity-controlled compression ignition engine, while the high-reactivity dimethyl ether was directly introduced into the cylinder to realize the reactivity stratification. In this study, computational investigations of dimethyl ether reforming and syngas/dimethyl ether reactivity-controlled compression ignition engine were respectively realized by the COMSOL software and the KIVA-3V code. The influences of the exhaust valve opening timing, the premix ratio, and the reformer number on the performance of the reformer and the reactivity-controlled compression ignition engine were studied. The results indicated that the earlier exhaust valve opening timing and the more reformer number are beneficial for the dimethyl ether reforming and energy recovery, and the effect of the premix ratio is relatively minor. For the test system, the highest exhaust energy that can be applied for the dimethyl ether reforming is around 25 %, and 8.8 % of the exhaust energy can be recovered into the fuel energy to realize the increase of the fuel energy. The highest conversion rate of dimethyl ether to syngas is 78 %, and the fuel energy is increased by 6.37 % after the reforming. With the introduction of the fuel reforming system, the improvement of the system thermal efficiency is between 0.52 % and 1.44 %. To realize the moderate, efficient, and clean combustion of the dimethyl ether on-board reforming reactivity-controlled compression ignition engine, the dimethyl ether conversion rate should be further improved at a lower exhaust temperature.

The Effect of Spark-Plug Heat Dispersal Range and Exhaust Valve Opening Timing on Cold-Start Emissions and Cycle-to-Cycle Variability

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The partnership for advancing combustion engines (PACE) is a US Department of Energy consortium involving multiple national laboratories and includes a goal of addressing key efficiency and emission barriers in light-duty engines fueled with a market-representative E10 gasoline. A major pillar of the initiative is the generation of detailed experimental data and modeling capabilities to understand and predict cold-start behavior. Cold-start, as defined by the time between first engine crank and three-way catalyst light-off, is responsible for a large percentage of NOx, unburned hydrocarbon and particulate matter emissions in light-duty engines. Minimizing emissions during cold-start is a trade-off between achieving faster light-off of the three-way catalyst and engine out emissions during that period. In this study, gaseous and soot emissions were measured at a distance representative of the three-way catalyst position downstream of the engine at a 2 bar net indicated mean effective pressure (NIMEP) steady-state operating condition representative of cold-start. The test matrix included sweeps of ignition timing 15 degrees-before to 10 degrees-after top dead center firing (TDC&lt;sub&gt;f&lt;/sub&gt;) across three different spark-plug heat dispersal ranges (HR). Additionally, the effect of varying exhaust valve opening (EVO) timing on combustion stability and emissions was also studied. Results show that the spark plug HR affects the coefficient of variation (COV) of NIMEP under all cold-start conditions, while the impact on emissions was found to be minimal. At very retarded spark timings, colder spark plugs required higher air and fuel flow to maintain the desired 2bar NIMEP load, but the fraction of fuel energy going into the exhaust was found to be similar for all spark plugs. Retarding exhaust valve timings showed a simultaneous reduction in emissions while increasing the fraction of fuel energy being fed into the exhaust. However, engine COV was also observed to increase with retarded exhaust timings.&lt;/div&gt;&lt;/div&gt;

Effects of intake valve opening duration on performance optimization of an Atkinson cycle engine under part load

A comprehensive analysis of the intake valve opening duration (IVOD) effects on the performance of an Atkinson cycle engine is conducted in this work using numerical simulation and experimental validation. Through one-dimensional simulation, the relationship between the range of IVOD and the compression ratios is firstly investigated under the constraint of compression pressure. Two representative IVOD, 295 and 314°CA, are then respectively applied to the performance simulation and experiment of a practical Atkinson cycle engine. The simulation shows the combination of a late intake valve opening timing (IVO) angle and a late exhaust valve opening timing (EVO) angle is profitable for improving the fuel economy under part load operating conditions (i.e. 2000 rpm@2 bar and 3000 rpm@3 bar). The experimental results present the Atkinson cycle engine under both IVOD scenarios considerably improves the brake specific fuel consumption (BSFC) and reduces the pumping mean effective pressure (PMEP) compared to those of the original Otto cycle engine. Meanwhile, the comparison between two IVOD scenarios show that the shorter IVOD leads to an improvement of indicated thermal efficiency, especially at lower load. Considering fuel economy, a shorter IVOD is more favorable at part load for the Atkinson cycle engine. Two main contributions of this work are to numerically quantify the IVOD range for the Atkinson cycle engine under part load, and to experimentally validate the effectiveness of simulation. The findings of this work are expected to support the design of Atkinson cycle engines and provide a guideline of IVOD optimization under part load.

Quantitative analysis on the effects of compression ratio and operating parameters on the thermodynamic performance of spark ignition liquefied methane gas engine at lean burn mode

In this study, a thermodynamic analysis for the liquefied methane gas (LMG) engine with the variation of compression ratio (CR) was conducted through theoretical and experimental investigations. Firstly, the equations for thermodynamic cycle efficiency were further corrected based on the previous studies, in which the losses due to heat release rate (HRR), exhaust valve opening (EVO) timing, specific heat ratio, incomplete combustion and heat transfer were considered. Then, the sweeping test of CR was conducted on an LMG engine. On this basis, the thermodynamic cycle process was studied and various kinds of energy losses were analyzed. The results show that the improvement of indicated thermal efficiency by increasing CR mainly depends on engine operating conditions, the maximum of which occurs at high load and is close to the theoretical value (4.2 percent points). The actual cycle efficiency of LMG engine is mainly influenced by the specific heat ratio of medium gas, followed by the heat transfer loss and the effective expansion ratio (EER) loss. Compared with combustion duration, the combustion phase plays a much more important role in EER loss. All these have provided theoretical basis and direction for the improvement of actual thermal efficiency of LMG engine.

Realizing stratified mixtures distribution in a hydrogen-enriched gasoline Wankel engine by different compound intake methods

This work aimed to realize stratified mixtures distribution in a hydrogen-enriched compound-intake gasoline Wankel engine by utilizing the difference of gas velocity from different intake ports. A three-dimension computational fluid dynamics (CFD) WRE model was established to investigate the mixture formation and combustion process under five different intake modes, i.e. the way of the binary fuel enters the combustion chamber through different intake ports (side intake port, peripheral intake port or both port). The intake mode S-HGP (the mixtures of H2, gasoline and air are in the peripheral intake port and pure air is in the side intake port) realized an optimal equivalence ratio distribution, in which condition, the most fuels gather near the spark plug and the minority fuel in the rear region of the combustion chamber. Since the unburned mixtures always exist in the rear region of the chamber due to the mainstream in the WRE, the stratified distribution of S-HGP could consume most of the fuel. Because the faster flame propagation release a large amount of heats near top dead center (TDC), S-HGP possesses the highest average in-cylinder pressure under five intake modes, is about 1.264 times than the worst intake mode. Moreover, S-HGP has the maximum average in-cylinder temperature, the ideal thermal condition and moderate lean combustion get the lowest CO emission, comparing with the intake mode performing the highest CO emissions, the CO emission of S-HGP is decreased by 745% near the exhaust valve opening timing (210 °CA ATDC). However, owing to the higher temperature inside cylinder, S-HGP has slightly high NO emission. In conclusion, the results mean that compound intake combined with intake modes control is an effective method for fuel distribution optimization besides the fuel direct injection.

Implementing variable valve actuation on a diesel engine at high-speed idle operation for improved aftertreatment warm-up

Aftertreatment thermal management is critical for regulating emissions in modern diesel engines. Elevated engine-out temperatures and mass flows are effective at increasing the temperature of an aftertreatment system to enable efficient emission reduction. In this effort, experiments and analysis demonstrated that increasing the idle speed, while maintaining the same idle load, enables improved aftertreatment “warm-up” performance with engine-out NOx and particulate matter levels no higher than a state-of-the-art thermal calibration at conventional idle operation (800 rpm and 1.3 bar brake mean effective pressure). Elevated idle speeds of 1000 and 1200 rpm, compared to conventional idle at 800 rpm, realized 31%–51% increase in exhaust flow and 25 °C–40 °C increase in engine-out temperature, respectively. This study also demonstrated additional engine-out temperature benefits at all three idle speeds considered (800, 1000, and 1200 rpm, without compromising the exhaust flow rates or emissions, by modulating the exhaust valve opening timing. Early exhaust valve opening realizes up to ~51% increase in exhaust flow and 50 °C increase in engine-out temperature relative to conventional idle operation by forcing the engine to work harder via an early blowdown of the exhaust gas. This early blowdown of exhaust gas also reduces the time available for particulate matter oxidization, effectively limiting the ability to elevate engine-out temperatures for the early exhaust valve opening strategy. Alternatively, late exhaust valve opening realizes up to ~51% increase in exhaust flow and 91 °C increase in engine-out temperature relative to conventional idle operation by forcing the engine to work harder to pump in-cylinder gases across a smaller exhaust valve opening. In short, this study demonstrates how increased idle speeds, and exhaust valve opening modulation, individually or combined, can be used to significantly increase the “warm-up” rate of an aftertreatment system.

Analysis of scavenge port designs and exhaust valve profiles on the in-cylinder flow and scavenging performance in a two-stroke boosted uniflow scavenged direct injection gasoline engine

In this study, effects of intake scavenge port designs and exhaust valve opening profiles were studied on the scavenging process in a newly proposed two-stroke boosted uniflow scavenged direct injection gasoline engine by detailed three-dimensional engine simulations. As the most important geometric parameters, the axis inclination angle and swirl orientation angle of scavenge ports, as shown in Figure 1, were investigated and optimized for best scavenging performances at first. With the optimal axis inclination angle of 90° and swirl orientation angle of 20°, various combinations of scavenge port opening timing, exhaust valve opening duration and exhaust valve opening timing were then analysed. Four distinct scavenging periods, that is, early backflow period, backflow scavenging period, main scavenging period and post backflow period, were identified and their impacts on the in-cylinder flow motions and scavenging performances were investigated. The results show that the optimal scavenging performance can be achieved with a higher delivery ratio, charging efficiency and scavenging efficiency when the post backflow is just avoided by tuning the difference between the closing timings of scavenge ports and exhaust valves (Δ close) and the overlap between the opening profiles of scavenge ports and exhaust valves (Δ overlap) for a specific exhaust valve opening duration. A longer exhaust valve opening duration can be used to further improve the scavenging performances. In addition, the difference between the opening timings of scavenge ports and exhaust valves (Δ open) can be increased to improve scavenging efficiency. The Δ close also shows strong positive correlation with in-cylinder swirl ratio and negative correlation with tumble ratio. The results presented in this study provide the fundamental knowledge of the scavenging process in the uniflow scavenged two-stroke engine and assist the design of scavenge ports and valve strategies to optimize in-cylinder flow motion and scavenge performances in the two-stroke boosted uniflow scavenged direct injection gasoline engine with a variable valve actuation system for exhaust valves.

Thermodynamics-based mean-value engine model with main and pilot injection sensitivity

This paper presents a thermodynamics-based mean-value engine model that predicts the temperature and pressure at the end of each discrete combustion phase, the peak temperature and pressure, and the indicated mean effective pressure. The model has sensitivities to the engine speed, the main and pilot injection quantities and timings, and the temperature and pressure conditions in the intake and exhaust manifolds. Mathematical relationships are established between the input variables and the output variables through the thermodynamic principles of the modified ideal-gas-limited pressure cycle. Modifications to the ideal-gas cycle include the pilot combustion stage, the effective compression ratio based on the fuel injection timing and start of combustion, the effect of the constant-volume burn ratio on combustion, and the exhaust valve opening timing. The model is also augmented with empirical correlations for the ignition delay, the constant-volume burn ratio, and the heat transfer in order to improve the fidelity of the model. It is validated using test data from a Ford 6.7 l diesel engine. Unlike most data-regression-based mean-value engine models, the model presented in this paper does not sacrifice essential details of the underlying physics while providing a computationally efficient simulation tool.

Fuel economy analysis of part-load variable camshaft timing strategies in two modern small-capacity spark ignition engines

Variable Camshaft Timing strategies have been investigated at part-load operating conditions in two 3-cylinder, 1.0-litre, Spark Ignition engines. The two small-size engines are different variants of the same 4-valve/cylinder, pent-roof design platform. The first engine is naturally aspirated, port fuel injection and features high nominal compression ratio of 12:1. The second one is the turbo-charged, direct injection version, featuring lower compression ratio of 10:1. The aim of the investigation has been to identify optimal camshaft timing strategies which maximise engine thermal efficiency through improvements in brake specific fuel consumption at fixed engine load.The results of the investigation show that the two engines demonstrate consistent thermal efficiency response to valve timing changes in the low and mid part-load envelope, up to a load of 4bar BMEP. At the lower engine loads investigated, reduced intake valve opening advance limits the hot burned gas internal recirculation, while increasingly retarded exhaust valve opening timing favours engine efficiency through greater effective expansion ratio. At mid load (4bar BMEP), a degree of intake advance becomes beneficial, owing mostly to the associated intake de-throttling. In the upper part-load domain, for engine load of 5bar BMEP and above, the differences between the two engines determine very different efficiency response to the valve timing setting. The lower compression ratio engine continues to benefit from advanced intake valve timing, with a moderate degree of exhaust timing retard, which minimises the exhaust blow-down losses. The higher compression ratio engine is knock-limited, forcing the valve timing strategy towards regions of lower intake advance and lower hot gas recirculation. The theoretical best valve timing strategy determined peak fuel economy improvements in excess of 8% for the port fuel injection engine; the peak improvement was 5% for the more efficient direct injection engine platform.

A Comparison of Valving Strategies Appropriate for Multimode Combustion Within a Downsized Boosted Automotive Engine—Part II: Mid Load Operation Within the SACI Combustion Regime

Spark assisted compression ignition (SACI) is a combustion mode that may offer significant efficiency improvements compared to conventional spark-ignited combustion systems. Unfortunately, SACI is constrained to a relatively narrow range of dilution levels and top dead center temperatures. Both positive valve overlap (PVO) and negative valve overlap (NVO) strategies may be utilized to attain these conditions at low and intermediate engine loads. The current work compares 1D thermodynamic simulations of PVO valving strategies and a baseline NVO strategy in a downsized boosted automotive engine with variable valve timing capability. As future downsized boosted engines may employ multiple combustion modes, the goal of this work is the definition of valving strategies appropriate for SACI combustion at low to moderate loads and spark ignition (SI) combustion at moderate to high loads for an engine with fixed camshaft profiles. PVO durations, valve opening timings, and peak lifts are investigated at low to moderate loads and are compared to a baseline NVO configuration in order to assess valving strategies appropriate for multimode combustion operation. A valvetrain kinematic model is used to translate the desired valve lift profiles into camshaft profiles while a kinematic analysis is used to calculate piston to valve clearances and to define the practical limits of the PVO strategies. The NVO and PVO strategies are also compared to throttled SI operation at part load to assess the overall efficiency benefit of operating under the thermodynamic conditions of the SACI combustion regime. While the results of this study are engine specific, there are several camshaft profiles that are appropriate for the use of PVO rebreathing type valve events. For the range of PVO valve events examined and taking into consideration piston to valve interference, the use of high exhaust and low intake lifts with early exhaust valve opening timing and long PVO durations enables high levels of internal exhaust gas recirculation (EGR) with relatively low pumping losses.

SIMULATION OF THE COMBUSTION PROCESS IN THE ELECTRONICALLY CONTROLLED MARINE DIESEL ENGINE

The introduction of the electronically controlled low-speed diesel engines has raised a number of new problems caused mainly by the influence of these electronic system settings on the combustion process. The wide set of the combustion press settings is now available for the chief engineers on the board of the ship and for the shipyard experts during the sea trials. This opens many new possibilities for the combustion process optimization but also causes the danger of the serious engine malfunction due to the improper settings. The paper presents the mathematical model of the electronically controlled low-speed marine diesel engine ant the special attention is paid to the available settings of the combustion process. The effective compression ratio, the injection timing and the exhaust valve setting can be adjusted in a similar manner like in the actual engine. The combustion pressure curves, the mean indicated pressure, the exhaust gas temperature can be observed when changing the combustion settings. The paper describes in detail the results of the several most typical simulations like change of the given combustion pressure increase, the change of the effective compression ratio, the change of the exhaust valve opening timing and the change of the maximum load setting.

Fuel economy optimization of an Atkinson cycle engine using genetic algorithm

An Atkinson cycle engine with geometrical compression ratio (GCR) of 12.5 has been designed by maximizing fuel economy at full load operating conditions based on the Artificial Neural Network Method [1]. However, the Atkinson cycle engine generally operates at part load conditions especially in the middle to high load range. Optimization of the fuel economy for part load is more important in reducing the total fuel consumption. The Atkinson cycle engine applies the load control strategy that combines the intake valve closure (IVC) timing and electrically throttling control (ETC), which has an impact to the fuel economy. Moreover, the exhaust valve opening (EVO) timing, spark angle (SA) and air–fuel-ratio (AFR) also affect the fuel economy. If calibrating these operating variables over the entire operating range through experiments, the difficulty and cost will become a big issue. A physical model based optimization scheme by coupling MATLAB genetic algorithm (GA) and 1-D GT-Power simulation models of the Atkinson cycle engine are proposed. The GT-Power models were improved to accurately simulate the part load conditions, by calibrating parameters of the combustion and heat transfer sub-models using experimental data taken at various speed–load points covering the entire operating range. The fuel economy was optimized based on the part-load calibrated GT-Power models using the Genetic Algorithm. After each speed–load point was optimized, the control maps for the IVC timings, SA, etc. were obtained. Then these numerically optimized control maps were input into the engine control unit (ECU) as the initial values of the engine calibration, which were further experimentally optimized. The experimental results show that the part-load GT-Power models have sufficient prediction accuracy, with maximal error of 8.5%. After optimized by GA, the fuel economy was greatly improved over the operating range, with the maximal improvement up to 7.67%.

Improvement of Diesel Engine Performance by Variable Valve Train System

The effects of variable valve timing and lift are studied in order to improve the thermal efficiency of a diesel engine, while maintaining low emission levels. At high load conditions, early closing of one of the intake valves or early intake valve opening realizes an enhancement of swirl intensity without increased pumping losses, and retarded intake valve closing reduces the effective compression ratio, both of which result in an increased exhaust gas recirculation ratio and an advanced fuel injection timing. Consequently low NO x formation and an improved thermal efficiency can be achieved simultaneously. At low load conditions, the injected fuel is dispersed in the cylinder by air swirl because of the small fuel quantity, and the increased effective compression ratio achieved by the early intake valve closing becomes effective at reducing hydrocarbon emissions. It is confirmed that the variable valve timing and lift system introduced in this research can flexibly change the engine parameters that govern engine combustion at various engine operating conditions. As a result, a 40 per cent reduction of engine-out NO x emissions and 4 per cent improvement of fuel consumption in the New European Driving Cycle (NEDC) are achieved. Furthermore, low-end torque could be increased by 40 per cent, utilizing exhaust pressure pulsation by matching of exhaust valve opening timing, and the overlap of intake and exhaust valve opening around top dead centre in the intake stroke. To enhance these benefits a new piston chamber with deep valve pockets is developed and its effect is investigated.

Evaluation of the effect of engine, load and turbocharger parameters on transient emissions of diesel engine

The vital issue of exhaust emissions during transient operation of diesel engines has been studied so far mainly on an experimental rather than simulation basis, owing to the very high computational times required for the analysis of each transient cycle. The study of transient emissions, however, is extremely important to manufacturers, since newly produced engines must meet the stringent regulations concerning exhaust emissions levels. In the present work, a comprehensive two-zone transient diesel combustion model is used for a preliminary evaluation of the effect of various parameters on nitric oxide (NO) and soot emissions during transient operation after load changes. The parameters are divided into three categories according to the specific sub-system examined, i.e. engine, load and turbocharger. Demonstrative diagrams are provided for the development of NO and soot emissions during the transient event, which depict the effect of each parameter considered. Moreover, the peculiarities of each case are discussed mainly in relation to turbocharger lag effects. For the current engine-load configuration, it is found that exhaust valve opening timing and cylinder wall insulation affect considerably NO and soot emissions. Additionally, load characteristics as well as turbocharger (T/C) mass moment of inertia play an important role on the development of transient NO and soot emissions.