Split Injection Research Articles

Dynamics of the in sac cavitating flow for diesel spray with split injection strategy

IC engines consume a large amount of fuel and produce plenty of emissions, thus reducing fuel consumption, and emissions are important. Nozzle internal flow which dominates spray breakup is the key to improve spray atomization and reduce fuel consumption. In this study, microscopic imaging technique was employed to investigate the effects of needle oscillation and injection strategy on the nozzle internal flow under cold (20°C) and hot (140°C) conditions. Needle oscillation was found to affect spray morphology, leading to obvious spray asymmetry under both cold and hot conditions with stronger spray radial propagation under hot condition. Cavitation in the sac appeared when needle oscillated due to enhanced turbulence. Besides, cavitation in the sac was introduced when the needle was insufficiently open due to throttling, especially under hot condition because of reduced viscosity. By contrast, when the split-injection strategy was employed, cavitation was considerably boosted because of the consistent flow transition and the resultant throttling effect. Effective injection duration of the first injection governed the corresponding peak relative cavitation area. The appearance of cavitation was delayed during the initial stage for each split injection after the fuel flows out due to laminar flow regime.

Evaluating performance and emissions of a CI engine fueled with n-octanol/diesel and n-butanol/diesel blends under different injection strategies

Considering climate change and energy crisis, the high-carbon alcohol has become a popular substitute fuel for diesel engines. In this study, diesel (D100), n-octanol/diesel (D50O50), and n-butanol/diesel (D50B50) blends were tested in a single-cylinder CI engine to evaluate the effects of n-octanol and n-butanol on the engine combustion characteristics, performance, and emissions formation. During the testing, the engine was operated at two engine loads (30% and 50%) with two injection pressures (40 and 60 MPa) at 1200 rpm. Both single injection and split injection strategies were used. Experimental results suggest that D50O50 and D50B50could result in serious knocking combustion under certain conditions with the single injection strategy. In contrast, the split injection strategy can lower the peak pressure and peak heat release rate, and consequently mitigating the knocking tendency for D50O50 and D50B50. Besides, noticeable two-stage combustion was observed for D100 and D50O50 due to the NTC behavior of diesel and n-octanol. Generally, because of the lower fuel reactivity of n-octanol and n-butanol, the ignition delay periods of D50O50 and D50B50 were significantly extended with the single injection; however, the difference in ignition delay was not evident with split injection strategy. Moreover, D50O50 can exhibit the highest thermal efficiency with proper injection pressure, and combustion phasing, etc. NOx and black carbon can be simultaneously reduced by D50O50 with split injection at an injection pressure of 60 MPa. Nevertheless, adding n-octanol and n-butanol increased the HC emissions due to their lower fuel reactivity at all tested conditions.

On the Effects of Injection Strategy, Exhaust Gas Recirculation, and Intake Boost on TSCI With Wet Ethanol

Abstract Using a split injection of wet ethanol, where a portion of the fuel is injected during the compression stroke, has been shown to be an effective way to enable thermally stratified compression ignition (TSCI), an advanced combustion mode that aims to control the heat release process by enhancing thermal stratification, thereby extending the load range of low temperature combustion (LTC). Wet ethanol is the ideal fuel candidate to enable TSCI because it has a high latent heat of vaporization and low equivalence ratio sensitivity. Previous work has shown “early” compression stroke injections (−150 to −100 deg aTDC) have the potential to control the start of combustion (SOC) while “mid” compression stroke injections (−90 to −30 deg aTDC) have the potential to control in-cylinder thermal stratification, thereby controlling the heat release rate. In this work, a mixture of 80% ethanol and 20% water by mass is used to further study the injection strategy of TSCI combustion. Additionally, the impact of external, cooled exhaust gas recirculation (EGR), and intake boost on the effectiveness of a TSCI with wet ethanol to control the heat release process are investigated. It was found that neither external, cooled EGR, nor intake boost level has any impact on the effectiveness of the compression stroke injection(s) at controlling the burn rate of TSCI. External, cooled EGR has the potential to increase the overall tailpipe combustion efficiency, while intake boost has the potential to decrease NOx emissions at the expense of combustion efficiency by lowering the global equivalence ratio.

Tailoring thermal stratification to enable high load low temperature combustion with wet ethanol on a gasoline engine architecture

Wet ethanol is a biofuel with unique fuel properties: a high latent heat of vaporization and low equivalence ratio sensitivity. These two fuel properties enable control over the heat release process in low temperature combustion through the enhancement of in-cylinder thermal stratification. In this work, it is shown that the direct injection of wet ethanol 80 (80% ethanol, 20% water, by mass) during the intake stroke on a mid-compression ratio engine with a side-mounted gasoline direct injector does not fully premix with incoming air, leaving stratification in the cylinder which elongates the combustion process, enabling high-load low temperature combustion without engine-damaging knock. As a result, the load under naturally aspirated conditions was only limited by oxygen content as the global equivalence ratio approached stoichiometry. The results show that swirl can not only modulate the induced stratification effectively by increasing the amount of bulk motion in the cylinder but also cause a thermal efficiency penalty, since swirl increases heat transfer losses. Modulation over the induced stratification can be achieved without an efficiency penalty by employing either a dual injector system where a fraction of the total fuel is injected into the port or a split injection strategy where a fraction of the total fuel is injected during the compression stroke. This strategy enables high-load low temperature combustion, while reducing the number of regions that form NOx and avoiding excessively rich regions that contribute to combustion inefficiency.

Effects of Multi-stage Pilot Split Injection Strategy on Combustion and Emission Characteristics in a Single-Cylinder Diesel Engine

Effects of Multi-stage Pilot Split Injection Strategy on Combustion and Emission Characteristics in a Single-Cylinder Diesel Engine

Effect of injection parameters and EGR on performance and emissions in a CRDI engine fuelled with cashew nut shell biodiesel blend

Stringent emission norms and requirement of energy security facilitate researchers to explore the use of alternate fuels and work on methods to optimise fuel injection parameters. The effects of injection timings (ITs), split injection and exhaust gas recirculation (EGR) on performance and emission characteristics of diesel engine fuelled with cashew nut shell biodiesel blends are investigated. Initially, experiments are conducted with diesel, B5 and B10 with original IT of 14.2° bTDC with direct injection and are considered as base reading. The fuel injection is optimised (at 10.2° bTDC and 15% split injection), and the effect of EGR rate at this optimised condition is analysed. Experiments are conducted with diesel, B5 and B10 with EGR rates of 5%, 10%, 15% and 20% at optimised injection condition for various loads. NOx reduced by 67%, 68% and 56% for diesel, B5 and B10 at full load compared to base readings. Smoke emissions reduced by 3–3.5%, and CO emissions reduced by around 50% for diesel and biodiesel blends at full load.

Combustion and emission characteristics of an ultra-lean burn gasoline engine with dimethyl ether auto-ignition

To stabilize combustion and shorten combustion duration in ultra-lean homogeneous gasoline-air mixture conditions, the onset of combustion is initiated with the auto-ignition of direct injection dimethyl ether (DME) only through compression in a single-cylinder four-stroke gasoline engine at the lambda of 2.1 at fixed cycle energy. The results show that the heat release processes are dependent on the total DME energy fraction in a cycle in the case of single and split direct injection and the DME fraction in each injection in the case of split direct injection. Increased total DME energy fraction in a cycle decreases the in-cylinder temperature to start low temperature combustion. High DME energy fraction in the second direct injection at a fixed total DME energy fraction in a cycle advances ignition timing, shortens combustion duration and decreases cycle-by-cycle variation of combustion while nitrogen oxides emissions increase although hydrocarbon and carbon monoxide emissions decrease simultaneously. The decrease of the total DME energy fraction in a cycle or that of DME fraction in the second injection at a fixed total DME energy fraction in a cycle is beneficial to the reduction of NOx emissions.

Spray dynamics and evaporation in a multihole GDI injector for pulsatile and split injection at elevated ambient pressure and temperature conditions

The evolution of pulsatile and split injection spray from a multihole, Gasoline Direct Injection (GDI) atomizer at different ambient conditions is examined experimentally and computationally. The fuel is injected at 80 bar for a duration of 1.2 ms (for single injection) and also for different split proportions (ranging from 0.3 ms to 0.9 ms for the first injection and 0.9 ms to 0.3 ms for the second injection). The influence of different split proportions on the spray characteristics such as spray penetration length, cone angle and droplet size is studied in detail, and they are compared against those of single injection case to highlight the differences. Experiments were conducted in a constant volume chamber for elevated ambient pressures. The fuel spray was visualized using high-speed shadowgraph technique. Three-dimensional spray simulations were carried out using ANSYS FLUENT 16.1. The RANS-DPM coupled simulations were performed for higher ambient pressure and temperature conditions. Good agreement between the experiments and simulations is achieved with respect to spray penetration length and cone angles for both single and split injection strategies. For larger proportion of the first injection, the interaction of the second spray with the rear of the first spray was prominent at higher chamber pressure. The spray penetration length was found to reduce for split injection strategy for all ambient pressure conditions. The spatio-temporal evolution of vapour plumes in terms of equivalence ratio highlights the possibility of attaining near homogeneous, rich mixture or a stratified mixture depending on the split proportion and dwell time.

Numerical study of the effect of split direct injection on the lean-burn combustion characteristics in a poppet-valve two-stroke gasoline engine at high loads

Poppet-valve two-stroke gasoline engines can increase specific power of four-stroke gasoline engines with the same displacement. But knocking combustion may also occur at high loads in two-stroke engines. The application of stratified lean-burn on poppet-valve two-stroke gasoline engines can avoid knocking and increase combustion stability. To investigate the effect of the mixture stratification on lean-burn events at high loads, simulation was conducted in different split direct injection conditions with constant fuel mass when equivalence ratio is 0.625. Results show that most fuel distributes near the center of the cylinder at any second direct injection ratio ( rSOI2). At different rSOI2s, auto-ignition occurs during flame propagation, causing shortened combustion duration. Auto-ignition causes the second peak of the heat release rate. The second peak of the heat release rate first decreases and then increases with increased rSOI2. Indicated mean effective pressure and indicated thermal efficiency increase with increased maximum pressure rise rate. The maximum indicated thermal efficiency of 42% can be reached without knocking combustion at 1500 rpm. The proportion of fuel mass through auto-ignition in the cylinder is an important factor to change the indicated thermal efficiency of a lean-burn engine at high loads.

Effects of GDI injector deposits on spray and combustion characteristics under different injection conditions

Injector deposits, which deteriorate the combustion and emissions, are frequent in gasoline direction injection (GDI) engines. An objective of this paper was to investigate the effects of the GDI injector deposits on the spray and combustion characteristics in a constant volume chamber (CVC) and an optical GDI engine, respectively, using different fuel temperature, injection pressure, and injection strategies. The spray and tail droplet characteristics were analyzed by using high-speed imaging. The combustion characteristics involving flame propagation, diffusion flame, and particle emissions were studied in a single-cylinder optical GDI engine. The results showed that the deposits slightly increased the spray penetration at 30 °C, and the deposits enhanced the flash-boiling process at the fuel temperatures of 60 °C and 90 °C. The influence of the deposits on flash-boiling was weakened at 20 MPa injection pressure. Compared with the clean injector, the fouled injector had smaller and lower speed tail droplets, slightly lower combustion flame speed, and slightly smaller peak in-cylinder pressure. Moreover, the fouled injector had much more tip diffusion flame compared with the clean injector. The split injection strategy increased the tip diffusion flame and soot emission for both injectors at a fuel temperature of 90 °C. The diffusion flame luminance was linear with the number concentration of accumulation mode particles, and the luminance of the diffusion flame can characterize the soot concentration. The tip diffusion flame caused by the deposits is the primary source of soot emission at a fuel temperature of 90 °C.

Effects of miller cycle strategies on combustion characteristics and knock resistance in a spark assisted compression ignition (SACI) engine

Spark assisted compression ignition (SACI) is a proven strategy to extend the operation load range and control the combustion phase of homogeneous charge compression ignition (HCCI) with high thermal efficiency. However, the occurrence of abnormal combustion, such as engine knock, limits SACI to operate in a wider load range. In this paper, the effects of Miller cycle on knock suppression effect and combustion characteristics are experimentally studied using a single-cylinder gasoline engine. Two types of Miller cycle tests under different boundary conditions are conducted: one is Miller cycle with constant negative valve overlap (NVO), and the other is Miller cycle with variable NVO while maintaining intake charge. The results show that different Miller cycle strategies can be used to adjust the ratio of fuel consumed by flame propagation and auto-ignition, and it is effective to optimize the combustion process in SACI to suppress engine knock while maintaining high efficiency. The results show that thermal efficiency of the optimized condition increased by 2.75% compared to the baseline. Besides, split injection strategy is also studied and the results show that a proper second injection timing (180-100 CAD BTDC) could moderate engine knock.

Split Injection Strategies for Biodiesel-Fueled Premixed Charge Compression Ignition Combustion Engine—Part I: Combustion, Performance, and Emission Studies

Abstract In this study, a single-cylinder research engine was used to investigate the comparative combustion, performance, and emissions characteristics of the engine in a premixed charge compression ignition (PCCI) mode combustion vis-a-vis baseline compression ignition (CI) mode combustion using three test fuels, namely, B20 (20% v/v biodiesel blended with mineral diesel), B40 (40% v/v biodiesel blended with mineral diesel), and mineral diesel. For both combustion modes, experiments were performed at constant fuel injection pressure (FIP, 700 bar), engine speed (1500 rpm), and fuel energy input (0.7 kg/h diesel equivalent). PCCI mode combustion experiments were performed at four different start of main injection (SoMI) timings using two different pilot fuel injection strategies, namely, single pilot injection (SPI, 35 deg before top dead center (bTDC)) and double pilot injection (DPI, 35 deg, and 45 deg bTDC). Results showed that advancing SoMI timing for both CI and PCCI combustion modes resulted in knocking; however, the DPI strategy resulted in relatively lesser knocking compared with the SPI strategy. The performance of PCCI mode combustion was relatively inferior compared with baseline CI mode combustion; however, biodiesel blends slightly improved the performance of PCCI mode combustion. Overall, this study shows that the PCCI mode combustion operating load range can be improved by using the DPI strategy.

Evaluation of performance and emission characteristics of a diesel engine using split injection

Society at large today is deeply concerned with environmental pollution which is primarily contributed by vehicular pollution. Diesel engines are mainly responsible for creating much of the air pollution. A large number of analyses have revealed numerous fuel alternatives with a view to mitigate emission, specially NOx and soot, and improve engine performance. This paper offers to explore the adequate balance between NOx and soot along with performance. The combined effect of split injection and piston bowl geometry on engine performance and emission has been investigated numerically. Numerical simulations were performed using three-dimensional AVL-FIRE commercial code on a single-cylinder DI Diesel engine taking standard diesel as fuel. Six different geometrical configurations of piston bowl along with three injection ratios were considered. The piston bowl geometry is modified by varying the depth and bowl radius keeping bowl volume, compression ratio, engine speed and mass injected invariant. It was noted that mass of fuel injected as pilot injection got mixed with the air, and the mixture became ready for burning prior to the occurrence of the main injection. In addition to this, the role of increasing the pilot injection mass up to 15% along with variation in piston bowl geometry on the in-cylinder mean pressure, temperature, rate of heat release and emission parameter is explored. Numerical data, computed for single injection, were validated against experimental results available in the literature. Further, an optimization study was undertaken for selected eighteen cases and results were evaluated for different injection ratios and piston geometries. Piston bowl geometry having 100 mm diameter and 2.48 mm depth and mass of fuel injected 5% in pilot and 95% in main injection (Case D4R1) was found to have optimum NOx and soot emission. The optimum NOx and soot were found to reduce by 10% and 16% by volume, respectively, as compared to those with single injection.

Experimental study on engine parameters variation in CRDI engine fuelled with palm biodiesel

The present research emphasizes on performance, combustion and emission parameters generated by palm oil methyl ester by means of multiple fuel injection strategies. Initially 20% of transesterified palm oil in diesel was tested with varying split injection quantities at 10%, 20% and 30% with a PI angle of 33° bTDC and MI angle of 23° bTDC. Superior performance with respect to fuel consumption, efficiency and emissions was achieved at 30% pilot-injection mass of POME20. At peak load condition, brake thermal efficiency of diesel@10% PI quantity, POME20 at 10%, 20% and 30% PI quantities was observed as 26.15%, 27.95%, 28.45% and 30.42% respectively. The combustion characteristics also enhanced for POME20@30% PI quantity. In emission perspective, NOx emissions for POME20 at 30% pilot-injection mass were 7.19% higher than the diesel fuel at 10% pilot-injection mass. In an effort to decrease NOx emissions for POME20@30% PI mass while retaining the same performance, three methodologies was investigated, such as usage of 10% EGR, decreasing injection pressure from 600 bar to 500 bar, advancing pre-injection timing from 33° bTDC to 53° bTDC. While comparing the outcomes, POME20-30% PI mass@10% EGR showed 2.4% and 0.55% more brake thermal efficiency than diesel and POME20 with a PI quantity of 10%@0% EGR. Nitrogen oxide outflows for POME20-30% PI mass@10% EGR were nearly equivalent to diesel-10% PI mass@0% EGR and 1.28% lesser than POME20-10% PI mass@0% EGR. Finally it was concluded that POME20-30% PI quantity@10% EGR would be a best potential strategy with respect to performance and emission viewpoint.

Effects of multiple uniformity split injection strategies on combustion and exhaust emission characteristics in a single-cylinder diesel engine

Effects of multiple uniformity split injection strategies on combustion and exhaust emission characteristics in a single-cylinder diesel engine

Improvement of valley splitting and valley injection efficiency for graphene/ferromagnet heterostructure**Project supported by the National Key R&D Program of China (Grant No. 2017YFF0206104), the National Natural Science Foundation of China (Grant No. 51871018), Beijing Laboratory of Metallic Materials and Processing for Modern Transportation, the Opening Project of Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics of Chinese

The valley splitting has been realized in the graphene/Ni heterostructure with the splitting value of 14 meV, and the obtained valley injecting efficiency from the heterostructure into graphene was 6.18% [Phys. Rev. B 92 115404 (2015)]. In this paper, we report a way to improve the valley splitting and the valley injecting efficiency of the graphene/Ni heterostructure. By intercalating an Au monolayer between the graphene and the Ni, the split can be increased up to 50 meV. However, the valley injecting efficiency is not improved because the splitted valley area of graphene moves away from the Fermi level. Then, we mend the deviation by covering a monolayer of Cu on the graphene. As a result, the valley injecting efficiency of the Cu/graphene/Au/Ni heterostructure reaches 10%, which is more than 60% improvement compared to the simple graphene/Ni heterostructure. Then we theoretically design a valley-injection device based on the Cu/graphene/Au/Ni heterostructure and demonstrate that the valley injection can be easily switched solely by changing the magnetization direction of Ni, which can be used to generate and control the valley-polarized current.

Computational Modeling of Diesel Spray Combustion with Multiple Injections

<div class="section abstract"><div class="htmlview paragraph">Multiple injection strategies are commonly used in conventional Diesel engines due to the flexibility for optimizing heat-release timing with a consequent improvement in fuel economy and engine-out emissions. This is also desirable in low-temperature combustion (LTC) engines since it offers the potential to reduce unburned hydrocarbon and CO emissions. To better utilize these benefits and find optimal calibrations of split injection strategies, it is imperative that the fundamental processes of multiple injection combustion are understood and computational fluid dynamics models accurately describe the flow dynamics and combustion characteristics between different injection events. To this end, this work is dedicated to the identification of suitable methodologies to predict the multiple injection combustion process. Two different approaches: Representative Interactive Flamelet model (RIF) and Tabulated Flamelet Progress Variable (TFPV) are compared and multiple n-dodecane Spray A injections from the Engine Combustion Network are simulated using the RANS methods with both standard <i>k</i> − <i>ε</i> and <i>k</i> − <i>ω</i> SST models. Evaluations of different turbulence and combustion models are carried out by comparing computed and measured data in terms of the mixing, penetration, first- and second-stage ignition characteristics, flame structures and soot formation.</div></div>

Study on effects of split injection proportion on hydrogen mixture distribution, combustion and emissions of a gasoline/hydrogen SI engine with split hydrogen direct injection under lean burn condition

Split hydrogen direct injection is proved to be a better way to use the hydrogen in the engine. Therefore, a numerical study on effects of split injection proportion on hydrogen mixture distribution, combustion and emissions was presented of a gasoline/hydrogen SI engine with split hydrogen direct injection to investigate the principle of split hydrogen direct injection. Under lean burn condition, six different split injection proportions achieve six kinds of hydrogen mixture distribution, which affect the engine performance a lot. With split hydrogen direct injection, the mixture nearby the spark plug is denser and in other zone is more homogeneous at the same time, which achieve better performances of both efficiency and emissions. As the first injection proportion increases, the cylinder pressure climbs to the highest with first injection proportion of 33% and the NOX, CO and HC emissions decrease continually. When the first injection proportion is 75%, the NOX, CO and HC emissions are respectively 31.6%, 79.3% and 40.6% less than those of single hydrogen direct injection.

Investigations on effect of split and retarded injection on the performance characteristics of engines with cashew nut shell biodiesel blends

ABSTRACT Efforts to improve air quality have led to use of alternate fuels and design modification that includes optimisation of fuel injection parameters. The effects of Injection Timings (IT) and split injection on performance and emission characteristics of a diesel engine with cashew nut shell biodiesel blends are experimentally investigated. The various blends, retarded timings and split injections used are vis-a-vis: B5 and B10, 2° crank angle (CA) and 4° CA from existing timing and 5%, 10%, and 15% of mass of main injection at 2200 rpm. NOx reduced by 17.8%,11.8%, 27.5% for diesel, B5, B10 respectively at 4° retarded CA with 10% split compared to base IT with single injection. Smoke reduced by 19.5%, 73.8% for diesel and B5 respectively at 4° retarded CA and 15% split. It is found that lower emissions are attained without affecting the performance for all fuel blends with retarded injection timing and split injections.

Study of using diesel/high-ON biofuel blends as the pilot fuel with large proportion and split injection in the dual-fuel combustion

Dual-fuel combustion using diesel and high-octane number (ON) biofuel of n-butanol blends to ignite compressed natural gas (CNG) with pilot fuel split injection was investigated. 30% n-butanol/70% diesel (B30D70) and pure diesel (B0D100) as the pilot fuels were compared with the start of pre-injection (SOIp) timings swept from −30 (SOIp30) to −80 °CA ATDC (SOIp80) under the CNG substitution rates of 50% at low load and 65% at medium load. A fixed start of main-injection (SOIm) timing of −9 °CA ATDC in B0D100 and various SOIm timings in B30D70 to match CA50 of B0D100 were employed. The experimental results indicated that adding n-butanol in the pilot fuel can significantly reduce the PM emission at advanced SOIp timings even with large proportion of pilot fuel. At low load, B30D70 reveals higher indicated thermal efficiency (ITE) due to its shorter combustion duration compared to B0D100, and it also leads to lower NOx emissions resulted from the more homogeneous mixture. The CO and THC emissions tend to be slightly increased in B30D70 for the advanced SOIp timings. At medium load, B30D70 also obtains higher ITE but yields higher NOx emissions. Relatively low level of NOx emissions can be obtained at early SOIp timings, such as SOIp60, SOIp70 and SOIp80. The CO and THC emissions are similar for the two pilot fuels at these timings. For the comparisons of the two pilot fuels and injection strategies, it can be demonstrated that B30D70 is more favorable to the thermal efficiency and emissions with split injection at SOIp40 under low load condition and early SOIp timings under medium load condition.