Low Engine Speed Research Articles

Numerical optimization of supercharging and combustion on a two-stroke compression ignition aircraft engine

Two-Stroke (2S) Compression Ignition (CI) engines have been used in aviation since World War II, for their excellent fuel efficiency and lightweight construction. In a modern light aircraft, these advantages still remain, along with the capability to run on jet fuel instead of gasoline. However, the design of these engines must be deeply revised, in order to incorporate the recent technologies, and it must be optimized with the support of CAE tools. The paper presents a CFD optimization of a turbocharged 2S CI 5.6 L flat-six aircraft engine developed by CMD. The scavenging system is of the Uniflow type, with exhaust poppet valves and a set of piston-controlled ports along the cylinder liner. Two mechanical superchargers are serially connected to the turbochargers. The crankshaft can be directly coupled to the propeller, thanks to its excellent balance and the relatively low maximum engine speed (2600 rpm). Differently from previous papers published on the same engine, the current study is focused on two crucial design topics: the optimization of the supercharging system and of the injection strategy. A customized version of KIVA-3V is used for the 3D-CFD cylinder analyses, while a commercial 1D-CFD code is employed to model the whole engine. The study is supported by a comprehensive experimental campaign, that permitted the accurate calibration of the numerical models. In comparison to any Four-Stroke delivering the same maximum power (400 HP at 2600 rpm, sea level), the analyzed engine is very light (about 220 kg), and efficient (211 g/kWh at typical cruise conditions). Despite the high performance, peak cylinder pressure and turbine inlet temperature at sea level are relatively low: 125 bar, 850 K. At rated power (360 HP@2400 rpm, sea level) combustion is complete and smoke-less, thanks to the optimization of the injection strategy, supported by the previous CFD analysis. The engine can operate at altitudes as high as 5500 m (18,000 feet), still delivering 270 HP at 2400 rpm, without relevant reduction of fuel efficiency. The key for the performance at high altitudes is the choice of the turbocharger considering the compressor choke limit easly reachable at high altitudes.

Emission characteristics and performance of SCR coated on DPF with different soot loads

Selective catalytic reduction (SCR) catalyst coated on diesel particulate filters (DPF), term as SDPF, become a popular subject of current research due to the capability of improving the NOx conversion efficiency and catalytic activity under low-temperature and low-load conditions. This study investigated the impact of SDPF emission characteristics and performance with different soot loads. The results showed that, soot load had little effect on engine fuel consumption. With the increase in soot load, the pressure drop and SDPF inlet temperature showed an upward trend, and the NOx conversion efficiency decreased sharply. NOx conversion efficiency was the result of competition between exhaust temperature and NO2 concentration. When the soot load was 9.97 g/L, SDPF lost the ability to reduce NOx emission. SDPF could reduce nucleation-mode particle number (PN) emission by 2–3 orders of magnitude, the filtration efficiency of nucleation-mode PN emission was the competition result between physical collection mechanism and chemical reaction. The particle diameter of particles with passive regeneration reaction with NO2 ranges from 10.8 to 45.3 nm. SDPF could reduce the accumulation-mode PN emission by 1–2 orders of magnitude, and the filtration efficiency of accumulation-mode PN emission was greatly affected by the physical collection mechanism. Increasing the soot load of SDPF could effectively reduce the nucleation-mode PN emission, but had no obvious effect on the accumulation-mode. At low engine speed, the filtration efficiency of nucleation-mode and accumulation-mode PN increased significantly with the increase in the SDPF soot loads. The maximum filtration efficiencies of nucleation-mode, accumulation-mode, and total PN were 99.93 %, 99.36 %, and 99.56 %, respectively. With the increase in soot load, the geometric mean diameter of SDPF-out increased.

Експериментальні дослідження термоакустичних двигунів з двофазним робочим тілом

A distinguishing feature of these days is the general tendency to decrease the temperature level of the waste heat of engines for power plants in industry, transport, and energy. These circumstances complicate the usage of traditional energy-saving technologies designed to transform this heat into mechanical work. Given the lack of effective technologies, large volumes of such heat emissions are lost. As an example, we can consider ship power engineering. On ships that are equipped with dual-fuel medium and low-speed engines, the thermal emissions of the cooling systems have a temperature of 355…365 K. Given the small exegetical potential, the use of such low-temperature waste energy sources by any heat engines is a difficult problem. Therefore, the task of improving existing energy-saving technologies or developing new ones remains relevant. Thermoacoustic technologies can be useful in solving this problem. A significant advantage of thermoacoustic heat machines is the ability to use any external heat source, in this case low-temperature sources, and produce mechanical work. There are known cases of thermoacoustic oscillations at small temperature differences between heat sources under conditions of high humidity of the working environment. This phenomenon can be used to create low-temperature energy-saving systems based on thermoacoustic engines (TAE) with a wet two-phase working environment. The practical use of thermoacoustic systems as part of ship power plants requires additional research to solve low-level issues, in particular, increasing the specific power of the TAE. This work provides a description of the experimental equipment, design of experimental TAE with a wet working body and research methods. The results of the experiments showed that in experimental TAEs with a two-component (moist) working environment, the temperature of spontaneous thermoacoustic oscillations was 355…359 K, while the longitudinal temperature gradient in the matrix was 1.19…1.30 K/m. The specific power of TAE with a moist environment increased by 1.7…7 times, and the acoustic pressure increased by 2…4.7 times compared to the operation in dry air. It is shown that in the existing TAEs, the condensation of water vapor in the ceramic matrix and on the surfaces of the heat exchangers can lead to a loss of power, roughly up to 25 %, while maintaining the operational capacity.

Experimental and numerical investigation of the auto-ignition characteristics of cylinder oil droplets under low-speed two-stroke natural gas engines in-cylinder conditions

Auto-ignition of cylinder oil droplets in the cylinder of low-speed two-stroke gas engines may cause the pre-ignition. To verify and understand the mechanism of the auto-ignition of cylinder oil droplets, experimental research and numerical analysis were carried out to investigate the auto-ignition behaviors of cylinder oil droplets under in-cylinder conditions of low-speed two-stroke natural gas engines. The experimental equipment includes an optical rapid compression machine to simulate the engines’ in-cylinder conditions and a dual-camera system to capture the cylinder oil droplets' ignition processes. The numerical simulation model contains a transient multi-component evaporation model and a multi-step chemical reaction kinetic mechanism. The evaporation of cylinder oil droplets and the ignition of oil vapor in the cylinder of the rapid compression machine were simulated. The optical experiment verified that breaking a single large-size droplet into the droplet group consisting of the small basic droplets could greatly shorten ignition delay and form multiple ignition hot points intensifying the pre-ignition. The overall ignition delay decreases with the increase of the temperature for large oil droplets, while the ignition delay is not monotonous with the temperature change for small oil droplets. The ignition radius and the vapor/air ratio of ignition moment were obtained by combining experiment and simulation. The ignition radius is reduced as the temperature and pressure increase. And the vapor/air ratio of ignition moment could be reduced by decreasing ambient temperature and increasing ambient pressure. The effect of methane on the overall ignition delay of oil droplets depends on the initial droplet diameter. The auto-ignition of small-size single oil droplets could induce natural gas pre-ignition was valid. And these findings are beneficial to understanding the mechanisms of pre-ignition induced by cylinder oil droplets auto-ignition, and the design of low-speed two-stroke gas engines.

Rumbling, humming, booming – Perception of vehicle interior noise at low engine speeds

The reduction of fuel consumption of vehicles with combustion engines is a primary goal during the development of new vehicles. One approach to lower the fuel consumption is to reduce the engine speed. This changes the engine sound. Among others, low-frequency tonal components become audible. Sensations that are commonly associated with the perception of engine sounds with low-frequency tonal components are rumbling, humming and booming. Rumbling is characterized by a low-frequency tone that is amplitude modulated over time. Humming is elicited by an unmodulated low-frequency tone. The sensation of booming is an interaction of a low-frequency tone and modulated higher-frequency components. It is generally assumed that all these sensations have a negative impact on the pleasantness of the vehicle passengers, as they can cause tiredness and nausea. The present study investigates the influence of the stimulus characteristics on the above-mentioned sensations and the impact on the perceived pleasantness using psychoacoustic experiments. To explain the different sensations, artificial prototypical sounds were presented to the listeners prior to the experiment, which contained key stimulus properties for each sensation. The sensations were measured for recordings of vehicle interior sounds that were artificially manipulated to change the strength of the sensations. It is shown that not only the sensations change substantially but also the pleasantness, confirming a strong link between the sensations and pleasantness ratings. The results can form a basis for modeling these sensations and their impact on the pleasantness.

Effects of intake charge temperature and relative air-fuel ratio on the deterministic characteristics of cyclic combustion dynamics of a HCCI engine

Homogenous charge compression ignition (HCCI) combustion can significantly reduce automotive pollution and increase the thermal efficiency of the engine. However, combustion phasing control is a major challenge in HCCI engines due to severe cyclic combustion variations. This study investigates the cyclic combustion dynamics of the HCCI engine using nonlinear dynamic methods such as return maps, recurrence plots (RPs), and recurrence quantitative analysis (RQA). Combustion stability and cyclic variations of HCCI combustion parameters were investigated on a modified four-stroke diesel engine. The experiments were conducted by varying relative air-fuel ratios ([Formula: see text]) and intake air temperatures ([Formula: see text]) at two engine speeds. In-cylinder pressure data of 2000 consecutive engine combustion cycles is logged for each test condition. In this study, deterministic characteristics of combustion phasing (CA50) and crank angle position of maximum cylinder pressure ([Formula: see text]) are investigated and compared by employing nonlinear dynamical methods. Return maps revealed that [Formula: see text] is having distinct and more frequently observed deterministic characteristics in comparison to CA50. Patterns in RPs showed a more persistent and sudden change in the combustion dynamics at higher engine speeds. Recurrence plot-based analysis found the existence of deterministic features in the combustion dynamics irrespective of the operating conditions. It was found using RQA parameters that the deterministic nature becomes stronger with a decrease in [Formula: see text] and any deviation in intermediate values of [Formula: see text]. Additionally, RQA measures advocate that CA50 has more deterministic characteristics at higher engine speed while [Formula: see text] at lower engine speed. Strong coupling and synchronization between [Formula: see text] and CA50 is indicated by cross-recurrence plots and CPR index when engine operated with a comparatively richer mixture.

Performance Estimation of a Downsized SI Engine Running with Hydrogen

Hydrogen is a carbon-free fuel that can be produced in many ways starting from different sources. Its use as a fuel in internal combustion engines could be a method of significantly reducing their environmental impact. In spark-ignition (SI) engines, lean hydrogen–air mixtures can be burnt. When a gaseous fuel like hydrogen is port-injected in an SI engine, working with lean mixtures, supercharging becomes very useful in order not to excessively penalize the engine performance. In this work, the performance of a turbocharged PFI spark-ignition engine fueled by hydrogen has been investigated by means of 1-D numerical simulations. The analysis focused on the engine behavior both at full and partial load considering low and medium engine speeds (1500 and 3000 rpm). Equivalence ratios higher than 0.35 have been considered in order to ensure acceptable cycle-to-cycle variations. The constraints that ensure the safety of engine components have also been respected. The results of the analysis provide a guideline able to set up the load control strategy of a SI hydrogen engine based on the variation of the air to fuel ratio, boost pressure, and throttle opening. Furthermore, performance and efficiency of the hydrogen engine have been compared to those of the base gasoline engine. At 1500 and 3000 rpm, except for very low loads, the hydrogen engine load can be regulated by properly combining the equivalence ratio and the boost pressure. At 3000 rpm, the gasoline engine maximum power is not reached but, for each engine load, lean burning allows the hydrogen engine achieving much higher efficiencies than those of the gasoline engine. At full load, the maximum power output decreases from 120 kW to about 97 kW, but the engine efficiency of the hydrogen engine is higher than that of the gasoline one for each full load operating point.

Effect of Exhaust Gas Recirculation Combined with Selective Catalytic Reduction on NO x Emission Characteristics and Their Matching Optimization of a Heavy-Duty Diesel Engine.

Exhaust gas recirculation (EGR) and selective catalytic reduction (SCR) have become important technologies to reduce the NOx emission of heavy-duty diesel engines and meet the increasingly stringent emission regulations. This paper studied the effect of EGR combined with SCR on the NOx emission characteristics of a heavy-duty diesel engine based on the engine bench test. The results showed that the NO reduction rate of EGR-coupled SCR increased with the increase of engine load, and the effect was no longer significant when the NO reduction rate exceeded a certain limit under the same working conditions. EGR combined with SCR has little effect on NO2 emission reduction, and the increase of engine speed can significantly improve the efficiency of the NO2 reduction rate at 75 and 100% load. 25% opening of the EGR valve (OEV) and 50% OEV have very similar effects on the NOx reduction rate when the engine speed is at a low level. Compared with low engine speeds, increased OEV or ammonia NOx molar ratio (ANR) had a more obvious effect on the NOx reduction rate at high engine speeds. SCR combined with low valve-opening EGR had a more significant effect on the NOx reduction rate. The increase of OEV led to the increase of fuel consumption rate, but the effect on the fuel consumption rate decreased gradually with the increase of diesel engine speed. Meanwhile, this study optimized the matching relationship between OEV and ANR based on the data of the genetic algorithm, which provides a theoretical research method and application basis for diesel engine-matching of EGR and SCR.

Performance Optimization of the High-Pressure Compressor in Series Two-Stage Turbocharging System Based on Low-Speed Performance Requirements of Diesel Engine

Abstract The performance of the high-pressure (HP) compressor is very important for the two-stage turbocharging system. However, the performance of HP compressor on the engine most of the time is poor at low speed and low mass flow conditions. These will lead to poor engine performance at low engine speed. The purpose of this paper is to improve the performance of the HP compressor at low speed and low mass flow conditions. The Latin hypercube design of the experiment method is used to establish the Kriging model and global optimization by multi-objective genetic algorithm NSGA-II to optimal HP compressor. The simulation results indicated that the flow field within the compressor was improved and the high entropy generation area was reduced. The new design delayed the mixing between the tip clearance leakage vortex flow and main flow. The low-speed performance of the HP compressor was improved. The turbocharger gas stand tests and engine bench tests were carried out. The results showed that the efficiency and pressure ratio of the optimized design is increased by 2.1% and 3%, respectively. The engine achieved better performance in low-speed conditions. The pumping means effective pressure (PMEP) and intake airflow increased by 7% and 4.98%, respectively, while brake specific fuel consumption (BSFC) and soot emissions decreased by 0.56% and 32.8%, respectively.

Low-speed performance compensation of a turbocharged natural gas engine by intake strategy optimization

Power output at the low engine speed is limited for natural gas engines, even though the turbocharging technology is used. In this paper, the intake system of a turbocharged spark-ignition natural gas engine with 4 valves (2 intake valves and 2 exhaust valves) was optimized by considering the intake strategy effects on the engine torque output and fuel economy improvement. Firstly, a 1D numerical model with hierarchical 1D/3D approach based on GT-SUITE was developed and validated against the experimental data of engine torque and fuel consumption rate. This approach combined detailed analysis of in-cylinder flow, charge movement and combustion. Secondly, different intake strategies were designed and their effects on the intake mass flow rate and in-cylinder mass during the intake process, the swirl flow, tumble ratio and the turbulent kinetic energy during the compression process, the flame propagation and temperature distribution evolution after the spark ignition, and the pressure and heat release rate were numerically investigated. The results showed that compared with the original intake strategy, the asynchronized intake strategy (the intake valves close earlier and the intake valve lifts are reduced, while two intake valves have different intake strategy) reduces the backflow in the end of intake stroke, improves the in-cylinder swirl flow, increases the maximum heat release rate and shortens the combustion duration, and it is believed to be the optimized intake strategy. Finally, different cam profiles corresponding to the numerically designed intake strategies were applied to the bench test engine and the dyno experiments showed that the optimized intake strategy improves the torque and reduces the brake specific fuel consumption by 41.42% and 8.1% respectively at a low engine speed of 1200 rpm.

Influence of vehicle acceleration intensity on dual-mass flywheel elements and transmission load

Modern high-torque low-speed internal combustion engines (ICEs) generate torsional vibrations close in disturbance frequency to gearboxes natural oscillation frequencies. Effective absorption of such oscillations requires a new torsional vibration damper between the internal combustion engine and gearbox design, which is implemented in the form of a dual-mass flywheel (DMF). One of the main reasons for DMF failure is its spring components destruction. The article develops mathematical and simulation (in MATLAB Simulink environment) model of a car with DMF in the period of starting, which takes into account the dependence of torque and power of the internal combustion engine on the number of the crankshaft revolutions and uneven rotation, car inertial and stiffness parameters, road resistance. It is established that when the car starts in first gear, the maximum load on spring components of DMF and transmission occurs at the initial moment of clutch engagement and exceeds the maximum effective torque of the internal combustion engine 1.6 times, has a pronounced oscillatory character and stabilizes as the car accelerates. With smooth acceleration of a car, when torque of internal combustion engine reaches, but does not exceed its maximum value of 250 N‧m, elastic moment in transmission components is stabilized at 230 N‧m. During intensive acceleration and transition through the extremum on torque curve of internal combustion engine on number of crankshaft revolution, the maximum DMF spring components and transmission load initially doesn’t change significantly, but reduces the duration of oscillatory processes and elastic moment of 160 N·m after attenuation of oscillations. A similar nature of stress changes is observed in the elastic links of DMF, which eventually leads to their fatigue failure and DMF failure. To increase a DMF service life, it is advisable to accelerate a car when moving intensively, bringing a number of revolutions to a value that is located at the extreme of torque of internal combustion engine on its performance characteristic, followed by switching to the next gear.

Application and Development of Selective Catalytic Reduction Technology for Marine Low-Speed Diesel Engine: Trade-Off among High Sulfur Fuel, High Thermal Efficiency, and Low Pollution Emission

In recent years, the International Maritime Organization (IMO), Europe, and the United States and other countries have set up different emission control areas (ECA) for ship exhaust pollutants to enforce more stringent pollutant emission regulations. In order to meet the current IMO Tier III emission regulations, an after-treatment device must be installed in the exhaust system of the ship power plant to reduce the ship NOx emissions. At present, selective catalytic reduction technology (SCR) is one of the main technical routes to resolve excess NOx emissions of marine diesel engines, and is the only NOx emission reduction technology recognized by the IMO that can be used for various ship engines. Compared with the conventional low-pressure SCR system, the high-pressure SCR system can be applied to low-speed marine diesel engines that burn inferior fuels, but its working conditions are relatively harsh, and it can be susceptible to operational problems such as sulfuric acid corrosion, salt blockage, and switching delay during the actual ship tests and ship applications. Therefore, it is necessary to improve the design method and matching strategy of the high-pressure SCR system to achieve a more efficient and reliable operation. This article summarizes the technical characteristics and application problems of marine diesel engine SCR systems in detail, tracks the development trend of the catalytic reaction mechanism, engine tuning, and control strategy under high sulfur exhaust gas conditions. Results showed that low temperature is an important reason for the formation of ammonium nitrate, ammonium sulfate, and other deposits. Additionally, the formed deposits will directly affect the working performance of the SCR systems. The development of SCR technology for marine low-speed engines should be the compromise solution under the requirements of high sulfur fuel, high thermal efficiency, and low pollution emissions. Under the dual restrictions of high sulfur fuel and low exhaust temperature, the low-speed diesel engine SCR systems will inevitably sacrifice part of the engine economy to obtain higher denitrification efficiency and operational reliability.

Experimental energy and exergy analysis of turbocharged marine low-speed engine with high pressure exhaust gas recirculation

Exhaust gas recirculation (EGR) has been widely applied on marine low-speed engine for the Tier III standard. However, few studies focus on energy and exergy analysis to improve the deterioration of fuel economy caused by EGR. This study fills in this gap based on the related experiment. Results show that about 35% EGR rate could achieve the Tier III standard, while cylinder bypass (CB) may raise NOx due to the coupling of CB and exhaust receiver. Subsequent energy analysis shows that improving fuel consumption should start with reducing the energy of heat transfer and exhaust gas. But, the exergy analysis indicates that reducing the irreversibility will be more efficient. The irreversibility mainly comes from in-cylinder, turbocharger and intercoolers. According to the instantaneous in-cylinder exergy analysis, the corresponding irreversibility is due to charge mixing and combustion. Reducing temperature gradient and proportion of premixed combustion are effective methods to inhibit it. EGR has opposite impacts on in-cylinder irreversibility caused by combustion: it enhances this irreversibility by rising maximum temperature and prolonging combustion duration (25% load); but it also raises the proportion of premixed combustion, which will inhibit this irreversibility (100% and 75% load). As for the irreversibility from turbocharger, it is negatively correlated with EGR rate, because of CB reducing exhaust temperature. Whereas, due to the existence of EGR intercooler, the irreversibility caused by intercoolers are positively related with EGR rate.

Spark knock suppression in spark ignition engines with hydrogen addition under low and high engine speeds

The influence of hydrogen addition on spark knock characteristics is investigated under two engine speeds (2000 rpm and 4800 rpm) with experiments and chemical analyses to describe the effect of hydrogen addition on the high-speed knock as well as on the low-speed knock. The experimental results showed that the hydrogen addition of 15 HV% advances the knock limit by 3°CA at 2000 rpm, while by 1°CA at 4800 rpm, indicating that the knocking suppression effect weakens at higher engine speeds. The chemical kinetic analyses showed that hydrogen addition reduces the heat release rate under 900 K where the low temperature oxidation (LTO) appears, while it promotes the heat release rate above 900 K. These results suggest that the smaller effect of hydrogen addition at the higher engine speed is due to the smaller dependence of the LTO on the ignition process, with the shorter residence time below 900 K.

Experimental study on the effects of ethanol blends on the combustion process, power performance and emission reduction of a motorcycle spark-ignition engine

This work investigates the effects of ethanol-blended gasoline fuels on a motorcycle engine's power performance and emission reduction compared with conventional gasoline fuel. Experiments were conducted on different ethanol-blended fuels E0, E30, E50, E85, and E100 for a spark-ignition motorcycle engine at various engine speeds and loads. The brake power increased with the ethanol blending ratio; E100 fuel produced the highest brake power, and E0 fuel made the lowest. The rise of ethanol in blends contributed to the retarding of ignition and reducing the peak combustion pressure and maximum heat release. The CO emission for E100 and its blends was less than gasoline fuel. The HC emissions decreased with the increase in ethanol blending ratio, and the difference was more considerable for E0 and E100 fuels at low engine speed than at higher engine speeds. Compared with E0 fuel, ethanol blends had lower NOx emissions and greater reduction levels.

High durability variable geometry turbine for commercial vehicle turbochargers

Abstract Transportation sector constitutes a major portion in the Green House Gas (GHG) emissions of the world. Reduction of GHG emission requires the development of highly efficient Internal Combustion Engines (ICE) which are downsized using turbochargers that provide compressed air for cleaner combustion. Variable Geometry (VG) turbochargers are widely accepted for this application because of the ability of VG turbine to function at wider flow range. This ensures the supply of compressed air at low engine speeds also. However, the interaction between stator vanes and turbine rotor has been a major issue in terms of High Cycle Fatigue (HCF) of such a turbocharger. Till now, a conservative design approach constrained the maximum rotation speed to below resonance speed for vibration mode 2. But, to achieve further downsizing it would be necessary to challenge higher rotation speeds. This paper will firstly introduce the tip-timing experiment and CFD-FEA simulations used to evaluate the HCF of VG turbine, and secondly it discusses the results of new VG turbine system which achieved safe operability even at vibration mode 3, both on simulation and experiment. The tip-timing experiment was conducted at 680°C on hot gas stand test bench with optical sensors installed circumferentially around the rotor tip. These measurements have been verified and validated with the safety factor calculated from blade surface pressure data obtained from transient rotor CFD simulations.

Reducing NOx Emissions through Microwave Heating of Aftertreatment Systems for Sustainable Transport in the Inland Waterway Sector

The inland navigation sector makes a significant contribution to the growth of the global economy as well as to climate change due to pollutants emitted by diesel engines. NOx emissions are very high in port areas where, due to traffic, the ships run at idling regimes. Selective catalytic reduction (SCR) represents one of the most suitable technologies, in terms of cost effectiveness, but does not perform well if the temperature during vessel operation is lower than 180 °C. Microwave technology can support preheating of the ceramic core of SCR in order to increase the temperature towards the optimal interval for the best NOx reduction. Research has focused on coupling a magnetron head to a SCR device in order to evaluate to what extent the technology can meet the requirements of Stage V of the European Directive related to NOx emissions. Measurements of NOx emitted have been performed on engines with 603.5 kW nominal power and 1500 rpm that operate at a lower engine speed (700–1200 rpm) and output power (58–418 kW). The values recorded for emissions using microwave heating of ceramic core of SCR have decreased by 89% for a constant load of engine and idling engine speed.

A Simulation Study on the Transient Behavior of a Gasoline Direct Injection Engine under Cold Start Conditions

<div class="section abstract"><div class="htmlview paragraph">The cold start process is critical to control the emissions in a gasoline direct injection (GDI) engine. However, the optimization is very challenging due to the transient behavior of the engine cold start. A series of engine simulations using CONVERGE CFD™ were carried out to show the detailed process in the very first firing event of a cold start. The engine operating parameters used in the simulations, such as the transient engine speed and the fuel rail pressure (FRP), came from companion experiments. The cylinder pressure traces from the simulations were compared with experiments to help validate the simulation model. The effects of variation of the transient parameters on in-cylinder mixture distribution and combustion are presented, including the effects of the rapidly changing engine speed, the slowly vaporized fuel due to the cold walls, and the low FRP during the first firing cycle of a 4-cylinder engine. Comparison was also made with non-transient steady state operation. It was shown that the injection-induced tumble ratio in the cylinder varied for different engine speed cases, resulting in a better fuel distribution in the low engine speed case. A relatively high turbulence level during the combustion process was seen in the transient engine speed case that led to strengthened combustion. The fuel tracking from the simulation indicated that about 30% of the fuel remained unreacted at a very late crank angle, in which 8% was in the gas phase and 22% in the liquid phase as wall films. As the FRP increased, the fuel droplets became smaller, and more fuel vaporized before hitting the piston. But the splash and rebound fuel fraction off the piston bowl was even less, resulting in a lower overall gas-phase equivalence ratio in the first firing event for the high FRP case. On the other hand, the fuel distribution was more homogeneous under the high FRP condition due to the high injection velocities. There should be an optimal FRP value, but it was difficult to discern since the peak pressures in different FRP cases were similar and turbulence levels varied in a non-monotonic way, as well, which would lead to cycle-to-cycle variations in the real engine.</div></div>

Understanding the role of turbulence-induced blade configuration in improving combustion process for hydrogen-enriched rotary engine

Benefits from the strong one-way flow within the rotor chamber, inducing turbulence is an effective means to improve flame evolutions and combustion characteristics of rotary engines. With the help of three-dimensional CFD simulations, the role of the turbulence-induced blade (TIB) configuration in strengthening ignition and combustion was assessed in a rotary engine fueled with hydrogen and gasoline, and the mixture formation, combustion process, and pollutants performance were addressed under different operating conditions. The numerical results show that introducing TIB in the rotor chamber is beneficial for improving the turbulent flow. The closer the blade position is to the spark plug, the higher the turbulent velocity and turbulent dissipation rate within the spark region. The leading-blade rotor chamber shows better combustion and emissions characteristics of the rotary engine. The TIB configuration is more sensitive to the combustion improvement of pure gasoline rotary engines compared with hydrogen-enriched rotary engines. The indicated power of the leading-blade engine is higher than that of the no-blade engine under various excess air ratio conditions. Especially for the excess air ratio of 1.1, the difference in the burned volume between the leading-blade and no-blade cases is more pronounced. Compared with stoichiometric operations, the TIB configuration shows better emission performance at lean-burn operations. The improvement of the turbulence level increases significantly by the leading-blade configuration at a lower engine speed. With the increase of the engine speed, the decrease in peak pressure is more significant in the leading-blade rotor chamber. The results shall give insights into the feasibility of the TIB configuration on the improvement of rotary engine performance in engineering applications.

Simulation study on transient performance of a marine engine matched with high-pressure SCR system

The high-pressure SCR system is suitable for low-speed marine engines that burn high-sulfur fuel, but it will cause the increase of the exhaust back pressure of main engine, which will affect the main engine’s performance and fuel consumption. At the same time, due to the large weight and size of the SCR reactor, the overall heat storage performance of the SCR reactor is large, which makes the temperature difference between the front and back of the turbine in the start-up and shutdown of the main engine and transient conditions, affecting the transient response performance of the turbine. In this paper, 6S46ME marine low-speed diesel engine and its high-pressure SCR system are taken as the research object, the co-simulation model is constructed by using GT-Suite coupled with a programming software, and the accuracy of the test model is verified. The influence of high-pressure SCR system on the performance of main engine is analyzed, and it finds that the fuel consumption of the main engine at low load increases significantly greater than that at high load, and the exhaust temperature of the main engine changes differently at different loads. On this basis, the co-simulation model was used to analyze the matching performance of high-pressure SCR system under the transient conditions such as the main engine Tier II/Tier III mode switching process, fast-loading, normal-loading and fast-unloading. The results show that the slow cut-in/cut-out of SCR reactor is beneficial to the stable operation of the main engine system, and the cut-in/cut-out time of high-pressure SCR system greatly affects the transient fuel consumption of the main engine, and the maximum increase of fuel consumption is about 3.6 g/kW·h; In addition, the thermal inertia of the reactor has a greater impact on the performance of the main engine at low load, but not at high load.