Multiple Injection Strategies Research Articles

Effects of different injection strategies on ignition and combustion characteristics in an optical PPC engine

abstract Although multiple injection strategies have a significant influence on partially premixed combustion (PPC) efficiency, the mechanisms behind the influence are still to be explained and evaluated. In this paper, single, double, and triple injection strategies are used in a heavy-duty optical engine. The effects on engine efficiency are analyzed by an energy balance method. Furthermore, the change of ignition location and combustion process under different injection cases are explored by natural luminescence recorded by a high-speed camera. The results show that, with double injections, the interaction between the main and pilot jets advances the combustion phasing nearly to the top dead center (TDC), resulting in higher efficiency. This interaction also shifts the combustion process into the piston bowl, where it has high potential to reduce heat-transfer loss. With triple injections, the interaction between the main combustion (formed by the pilot and main injections) and the post injection jet significantly affects the combustion losses. In all, the jet-jet interaction and combustion-jet interactions play a significant role in engine efficiency when using multiple injections.

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

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>

Artificial neural network approach on forecasting diesel engine characteristics fuelled with waste frying oil biodiesel

The present work investigates the influence of advanced injection strategy on a common rail direct injection assisted diesel engine characteristics fuelled with biodiesel and conventional diesel. Also, an artificial neural network is employed to forecast engine characteristics. Engine test is conducted under 100% load condition through an optimized nozzle opening pressure of 500 bar. Pre-injection timing is fixed permanently at 30 °CA bTDC, main injection timing varied from 15 °CA to 21 °CA bTDC and post-injection varied from 6 °CA bTDC to 6 °CA aTDC sequentially. However, the pre, main and post-injection quantities are changed respectively from 5% to 15%, 70% to 90%, and 5% to 15%. Minimum carbon monoxide, unburned hydrocarbon and smoke emission of 0.01% vol., 8 ppm and 1.59 FSN are achieved with pre-injection timing of 30 °CA, main injection timing of 21 °CA bTDC, and post injection timing of 6 °CA bTDC for B100-15%-70%-15%. Maximum brake thermal efficiency and nitric oxide emission of 34.3% and 1114 ppm are achieved in B100-5%-90%-5% at advanced injection timing and higher nozzle opening pressure. Artificial neural network models conform to experimental results having a lower root mean square error and correlation coefficient values in a range of 0.01 to 0.02 and 0.980 to 0.998 respectively. An artificial neural network is mostly preferred over other theoretical and empirical models to higher accuracy in predicting the output. Hence, multiple injection strategy fuelled biodiesel significantly decreased the emission and improved the performance compared to mechanical, single and split injection strategy.

Multiple injection for improving knock, gaseous and particulate matter emissions in direct injection SI engines

Advances in fuel injector technology have enabled research and development on a large variety of direct injection spark ignition (DISI) engine fueling strategies targeted to improve engine performance and reduce engine-out emissions. This study explores the effect of multiple injections on knock, engine efficiency and stability, and particulate number and gaseous emissions on a single-cylinder DISI research engine. Work to date on multiple injections in the literature is reviewed, and then two aspects of multiple injection strategies are experimentally investigated: the number of injections (up to five times in a cycle); and the timing of the injections (classified relative to the timing of intake valve opening and closing). A boosted, single-cylinder research engine equipped with a state-of-the-art piezoelectric hollow cone spray direct injector and research-grade E10 gasoline was used for the study. The results show multiple injections maintain torque and combustion stability compared with single injection and slightly increase the knock limits and indicated thermal efficiencies (maximum 0.7% absolute, 2.8% relative compared with single-injection baseline) due to improved heat release phasing, especially with an additional late injection during the intake valve closed (compression stroke) period. The gaseous pollutant emissions including nitrogen oxides and unburned hydrocarbons were reduced by 25% with multiple injections, particularly with injection during the compression stroke. In contrast, carbon monoxide emissions increased with multiple injections for all conditions. Increasing the number of injection events significantly reduced particulate number emissions (half with each additional injection), and the decrease in particulate number was not sensitive to the injection timing.

Effects of Rate-Shaped and Multiple Injection Strategies on Pollutant Emissions, Combustion Noise and Fuel Consumption in a Low Compression Ratio Diesel Engine

An experimental investigation has been carried out to highlight the effects of different injection strategies on the performance and emissions of a low compression ratio Euro 5 diesel engine operated with high EGR rates. Rate-shaped main injections, achieved with piezoelectric and solenoid injectors by means of boot and injection fusion, respectively, as well as optimized multiple injection patterns have been compared. The results of the comparisons, performed with reference to a state-of-the-art double pilot-Main (pM) strategy, are presented in terms of engine-out exhaust emissions, combustion noise (CN) and fuel consumption. Rate-shaped main injections, when included in delayed multiple injection patterns, have shown a minor influence on reducing NOx, while a slight deterioration in soot has been found. Both a double pilot and a boot injection schedule have been able to reduce CN at low loads. A higher reduction in CN has been obtained with an injection fusion event. Finally, DoE optimized triple and quadruple injection strategies have led to improved soot-NOx trade-offs, with respect to the pM calibration. In fact, splitting the injection helps to entrain air inside the fuel plumes, thus creating locally leaner mixture (less prone to forming soot) and allowing increasing the EGR rates (reducing NOx formation).

Stereoscopic high-speed microscopy to understand transient internal flow processes in high-pressure nozzles

The flow and cavitation behavior inside fuel injectors is known to affect spray development, mixing and combustion characteristics. While diesel fuel injectors with converging and hydro-eroded holes are generally known to limit cavitation and feature higher discharge coefficients during the steady period of injection, less is known about the flow during transient periods corresponding to needle opening and closing. Multiple injection strategies involve short injections, multiplying these aspects and giving them a growing importance as part of the fuel delivery process. In this study, single-hole transparent nozzles were manufactured with the same hole inlet radius and diameter as the Engine Combustion Network Spray D nozzle, mounted to a modified version of a common-rail Spray A injector body and needle. Needle opening and closing periods were visualized with stereoscopic high-speed microscopy at injection pressures relevant to modern diesel engines. Time-resolved sac pressure was extracted via elastic deformation analysis of the transparent nozzles. Sources of cavitation were observed and tracked, enabling the identification of a gas exchange process after the end of injection with ingestion of chamber gas into the sac and orifice. We observed that the gas exchange contributed widely to disrupting the start of injection and outlet flow during the subsequent injection event.

Measurements of the mass allocation for multiple injection strategies using the rate of injection and momentum flux signals

As legislations set very stringent environmental and fuel economy standards, researchers have pushed into a continuous development in all areas of the diesel engine. The recent evolution of the injection technologies has permitted to modify the fuel-delivery strategies. From what was a single pulse per injection event, modern systems allow to inject up to eight different times precisely per combustion cycle. In such sense, experimental results of the rate of injection and momentum flux could be useful for validation and improvement of computational models. Moreover, accurately quantifying the injected mass per pulse in a fuel–gas interface can provide data with more realistic engine-like conditions. To this end, this research presents measurements of the rate of injection and momentum flux for two simple multiple injection strategies: a pilot-main and a main-post. Boundary conditions included two rail and discharge pressures, two different pilot/post quantities and four dwell times. A new approach was employed to estimate the mass allocation with the momentum flux data, and results were compared to the rate of injection traces to verify the distribution calculated. On the results, signals for each pulse were successfully decoupled using its rising and falling edge. The shot-to-shot variability of the pilot/post injection was highly dependent on its transitory characteristics, and on the dwell time for post injections due to internal pressure waves. The injected mass per pulse was successfully measured as well in the momentum flux test rig, and the energizing time changed slightly to account for the different operation interfaces. Signals from both measurement campaigns showed a remarkable agreement when compared, ascertain the possibility of measuring the injected mass, and its allocation for multiple injection strategies, in the momentum flux test rig.

Investigation on an Injection Strategy Optimization for Diesel Engines Using a One-Dimensional Spray Model

Common rail systems have been widely used in diesel engines due to the stricter emission regulations. The advances in injector technology and ultrahigh injection pressure greatly promote the development of multiple-injection strategy, leading to the shorter injection duration and more variable injection rate shape, which makes the mixing process more significant for the formation of pollutant emission. In order to study the mixing process of diesel sprays under variable injection rate shapes and find the optimized injection strategy, a one-dimensional spray model was modified in this paper. The model was validated by the measured spray penetrations based on shadowgraphy experiments with the varying injection rate. The simulations were performed with five injection rate shapes, triangle, ramping-up, ramping-down, rectangle and trapezoid. Their spray penetrations, entrainment rates and equivalence ratios along spray axial distance are compared. The potentials of multiple-injection and gas-jet after end-of-injection (EOI) to improve mixing process and emission reduction are discussed finally. The results indicated that ramping-up injection rate obtains the highest entrainment rate after EOI, and it needs 1.5 times of injection duration for the entrainment wave to arrive at the spray tip. For the other four injection rates, the sprays can be treated as a steady-like state, needing twice of injection duration from EOI to the time the entrainment wave reaches the spray tip. The multiple-injection with proper injection rate shape enhanced the entrainment rate, and the gas-jet after EOI affected the mixture distribution and entrainment rate in spray tail under ramping-down injection rate.

Performance of a direct-injection natural gas engine with multiple injection strategies

This paper presents the experimental results for the performance of a direct-injection natural gas marine engine with different multiple injection strategies. In order to investigate the effects of natural gas post injection proportion and natural gas injection separation, a series of tests were performed at five different injection proportions (8%, 10%, 15%, 20%, 25%) and injection separation from 100μs to 700 μs at every 100 μs. The averaged cylinder pressure traces and combustion parameters (MFB50%, MFB90% and MFB5-90%) of each test point were calculated for combustion analysis. HC, CO and NOx emissions were collected to reveal the emissions characteristics. The results showed that the peak values of cylinder pressure and heat release rate will be lower than that of natural gas single injection strategy when multiple natural gas injection strategies are applied. Though the phase angle of 50% mass fraction burned is advanced at medium natural gas injection separations, the phase angle of 90% mass fraction burned is more likely to occur early at longer natural gas injection separations. With regard to emissions, HC and NOx emissions can benefit from using shorter natural gas injection separations while CO can only be reduced with small post injection proportions with certain natural gas injection separations.

Thermal effects on the diesel injector performance through adiabatic 1D modelling. Part II: Model validation, results of the simulations and discussion

In this paper, a one-dimensional computational model of the flow in a common-rail injector is used to compute local variations of fuel temperature (including the temperature change produced upon expansion across the nozzle) and analyse their effect on injector dynamics. These variations are accounted through the adiabatic flow hypothesis, assessed in a first part of the paper where the model features are also described. They imply variations in the fuel properties and the flow regime established across the injector internal restrictions driving the solenoid valve. An extensive validation of the model against experimental results is presented for a wide range of conditions. Multiple injection strategies are also explored, analysing the influence of the inlet fuel temperature and its variations on the mass injected by successive injections and the critical dwell time below which they cannot be separated. Results show significant changes in fuel temperature across some injector restrictions. These changes are greater the higher the rail pressure and lower the fuel temperature at the injector inlet. In the case of the flow across nozzle orifices, the fuel can be either heated or subcooled depending on the operating conditions, the heating being especially relevant for cold-start-like fuel temperatures at the inlet. Thermal effects also influence the injection rate and duration. This influence on injector dynamics is particularly accused in the injector of study due to its ballistic nature. In this regard, the time needed to effectively separate two successive injections is greater the higher the fuel temperature and the injection pressure.

A Study on Performance of Common Rail Direct Injection Engine with Multiple-Injection Strategies

Diesel engines are robust and reliable besides their good fuel economy. However, these engines produce higher exhaust emissions with fossil diesel and further these emissions level increases when operated on biodiesels. A common rail direct injection (CRDi) engine shows higher brake thermal efficiency (BTE) and lower emissions as compared to compression ignition mode (CI mode) of engine operation. This research paper revealed the results of diesel engine operated in CRDi mode with single injection (SI) and multi-injections (MI) of fuel using diesel and biodiesel of honne oil at 80% load. The CRDi engine operation with both SI and MI showed higher BTE and lower emissions as compared to CI mode. The peak pressure and heat release rate of a CRDi engine operation were lower as compared to CI mode. Overall, it could be concluded that biodiesel-powered CRDi engine with double injection and triple injection could reduce oxides of nitrogen (NOx) emissions by 40.8% and 50%, respectively, while smoke emission by 10% and 16.6%, respectively. However, there was a little penalty on BTE and brake-specific fuel consumption.

Investigation on pilot injection with low temperature combustion of Calophyllum inophyllum biodiesel fuel in common rail direct injection diesel engine

The present research work emphasises on the utilization of Calophyllum inophyllum biodiesel and preparation of 20% blend sample to explore the effects of variation of multiple injection strategies and amount of exhaust gas recirculation in a common-rail direct injection engine. In this aspects, the pilot injection quantity of B20 blend has been varied from 5 to 15% for the improvement of diesel engine characteristics. Among the tested results, an optimum pilot injection quantity has been identified and the same experimental work is extended for the addition of 10% and 20% exhaust gas recirculation under same operating conditions. The experimental study revealed that the increase in pilot injection rate from 5% to 15% at same operating conditions has shown higher brake thermal efficiency of 36.8% and the same improvement has not observed during exhaust gas recirculation addition. In terms of emissions point of view, the 15% pilot injection quantity of B20 fuel has resulted lowest hydrocarbon and carbon monoxide emissions when compared to diesel fuel by about 54.4% and 45.9% respectively. However, the implementation of 10% EGR rate at 15% pilot injection quantity reduced the oxides of nitrogen emission by 10.04%. On the other hand, the combustion characteristics are enhanced during increase in pilot injection rate and it decreased to lower level at higher concentration of EGR addition. Thus, the combined effect of 15% pilot injection rate and 10% EGR rate would be a best possible option for obtaining an improved performance and emission characteristics. Further, the study can be extended to vary the pilot injection, main and post injection timings with suitable EGR addition successful running of biodiesel blend.

Analysis on the effect of pilot injection strategies on combustion and emission characteristics of palm-munja biodiesel/diesel blend on CRDI diesel engine

Multiple injection strategy is a vital strategy to reduce the soot and NO x emissions concurrently. The multiple injection strategy can enhance the air/fuel mixture, combustion and exhaust emission characteristics by providing a small amount of fuel before the main injection. Among all types of alternate fuels, biodiesel has emerged as an eco-friendly fuel for the diesel engines. This paper is focusing on the effect of pilot injection strategies on diesel engine say timing (−30° bTDC to −50° bTDC) and by varying the fuel quantity (5–15%). The performance, combustion and emission characteristics of Palm-munja biodiesel/diesel blend (B20) were investigated on CRDI diesel engine. The experimentations were carried out on a constant speed by varying loads from 0 to 100%. The experimental results show that as an increase in pilot injection timing there is a reduction in the in-cylinder pressure, whereas soot and NO x emissions decrease as the pilot injection timing increases. As the pilot injection fuel quantity increases, the in-cylinder pressure and NO x emission increase, whereas soot emission decreases.

A comprehensive analysis of multiple injection strategies for improving diesel combustion process under cold-start conditions

Cold start in diesel engines is an issue of increasing importance due to its high fuel consumption and emissions. In cold-start operations, improving the combustion process is directly related to improving the thermal efficiency and emissions. In this study, a comprehensive analysis of multiple injection strategies was conducted under cold-start conditions to identify an optimal injection strategy that improves diesel combustion process at various ambient temperatures. The cold-start conditions were reproduced in a constant volume combustion chamber (CVCC). While all of the sprays in a single injection strategy were successfully ignited at 293 K, only the sprays near a glow plug showed combustion reactions at 253 K. The low air and diesel temperature at 253 K inhibited the diesel vaporization, which led to the poor combustion development. Pilot injections were implemented to improve the diesel vaporization at 253 K. The pilot injections had a small amount of heat required to vaporize diesel droplets, which reduced the temperature drop in the combustion chamber. The pilot injections also released small amounts of heat prior to the following main injection, thus aiding the vaporization of the main injection. The triple and quadruple injections improved the combustion process significantly at 253 K. However, the double and triple injections showed superior heat release rate and in-chamber pressure rise at 293 K. Based on the results at 253 K and 293 K, the triple injection strategy were determined to be the optimal injection strategy under cold-start conditions.

Combustion and emission characteristics of gasoline/hydrogenated catalytic biodiesel blends in gasoline compression ignition engines under different loads of double injection strategies

Gasoline compression ignition mode is one of the low-temperature combustion strategies using gasoline instead of diesel fuel and it is better than the other low-temperature combustion modes in terms of ignition controllability. Difficulty in the ignition at low loads and maximum pressure rise rate during high loads is the main problem in commercializing this engine. In order to solve this problem, hydrogenated catalytic biodiesel is blended with gasoline in different proportions and its combustion and emission characteristics under different working loads are investigated in a single injection mode. Stable combustion is achieved using this gasoline/hydrogenated catalytic biodiesel blends without any combustion assistance and increasing intake temperature. Results show that G70H30 blending fuel illustrates a comprehensively better combustion and emissions performance. However, the high maximum pressure rise rate at high loads and high particulate matter emission are the main problems. Hence, multiple injection strategies are applied for G70H30 to solve the above problem. It reveals that the particulate matter emission for 20% pilot injection ratio is lower than that of single injection mode. The maximum pressure rise rate of 20% or 30% pilot injection ratio can meet the engine limit. While the carbon monoxide and hydrocarbons emissions for double injection mode are higher than that of single injection mode and it increases with increasing pilot injection ratio.

Combustion stability study of partially premixed combustion by high-pressure multiple injections with low-octane fuel

This work is the second part of a study on low-load combustion stability for gasoline partially premixed combustion. In part 1, we investigated the sensitivity of the intake air temperature to combustion stability. In part 2, we evaluate the potential of the multiple-injection strategy along with the intake air temperature sensitivity to promote low-load combustion stability using low-octane gasoline fuel. The experiments were carried out in a fully transparent, single-cylinder, compression-ignition engine. The spray/wall interaction, particularly the fuel trapping in the piston crevice zone, was visualized by fuel-tracer planar laser-induced fluorescence for the first time in experiments. The in-cylinder combustion process of natural flame luminosity was captured by a high-speed color camera. By employing a multiple-injection strategy, the minimum intake air temperature can be further reduced from 70 °C (single injection) to 50 °C for target stable combustion. The combustion stability and engine performance were further improved by increasing the fuel injection pressure. For instance, with the triple-injection strategy at a higher fuel-injection pressure of 800 bar, the indicated mean effective pressure was increased by 24% when compared to that of the single-injection strategy. A stronger interaction among fuel spray jets, the piston, and the cylinder wall was observed for multiple injections with higher injection pressure, leading to higher unburned hydrocarbon (UHC) and carbon monoxide (CO) along with a more pronounced pool fire in the squish zone. The double-injection strategy resulted in lower UHC and CO emissions when compared to the triple-injection strategy. Applying a narrow spray angle injector with re-entrant combustion chamber is suggested for optimizing the spray/wall interaction.

Influence of fuel injection strategies on efficiency and particulate emissions of gasoline and ethanol blends in a turbocharged multi-cylinder direct injection engine

The effects of a broad range of fuel injection strategies on thermal efficiency and engine-out emissions (CO, total hydrocarbons, NOx and particulate number) were studied for gasoline and ethanol fuel blends. A state-of-the-art production multi-cylinder turbocharged gasoline direct injection engine equipped with piezoelectric injectors was used to study fuels and fueling strategies not previously considered in the literature. A large parametric space was considered including up to four fuel injection events with variable injection timing and variable fuel mass in each injection event. Fuel blends of E30 (30% by volume ethanol) and E85 (85% by volume ethanol) were compared with baseline E0 (reference grade gasoline). The engine was operated over a range of loads with intake manifold absolute pressure from 800 to 1200 mbar. A combined application of ethanol blends with a multiple injection strategy yielded considerable improvement in engine-out particulate and gaseous emissions while maintaining or slightly improving engine brake thermal efficiency. The weighted injection spread parameter defined in this study, combined with the weighted center of injection timing defined in the previous literature, was found well suited to characterize multiple injection strategies, including the effects of the number of injections, fuel mass in each injection and the dwell time between injections.

Numerical Study on the Effects of Multiple-Injection Coupled with EGR on Combustion and NOx Emissions in a Marine Diesel Engine

In this work, the potential of multi-injection strategies coupled with EGR to improve the trade-off relationship of NOx-BSFC (Brake specific fuel consumption) is carefully studied by multi-dimensional simulation using CONVERGE in a low-speed two-stroke diesel engine. The present study reveals that by introducing high EGR rate, the reduction of NOx emissions, the peak heat release rate and the peak pressure can be observed. But the effective fuel consumption rate is increased. We investigate the effects of various multiple-injection strategies on the engine performance, that is, single pilot-injection, single post-injection, single pilot-injection combined with single post-injection, and double pilot-injections, coupled with 39% EGR. The results show that low BSFC can be effectively achieved by a single pilot-injection strategy of small interval and large quantity. However, with a comprehensive consideration of low NOx emissions and BSFC, a strategy of 25 °CA pilot-main interval and 20% quantity should be chosen to obtain the best performance. The analysis of post-injection reveals that it is beneficial to reducing NOx emissions, but BSFC can be deteriorated. Moreover, it can be concluded that it is possible to achieve low NOx emissions and fuel consumption simultaneously by using the pilot-injection combined with post-injection. It also can be found that NOx emissions are deteriorated remarkably when using double pilot-injections.

Experimental and numerical study of multiple injection effects on combustion and emission characteristics of natural gas–diesel dual-fuel engine

Natural gas–diesel dual-fuel engines can significantly reduce soot emissions and mitigate the oil crisis. However, some drawbacks exist including low thermal efficiency, as well as high methane and carbon monoxide emissions. Multiple injection plays an important role in improving the performance and reducing emissions in dual-fuel engines. This paper presents an experimental and numerical study of multiple injection effects on the combustion and emission characteristics of a natural gas–diesel dual-fuel engine at low load condition. The results showed that, when the first diesel injection timing is advanced, the indicated thermal efficiency and nitrogen oxide emissions increased first and then decreased, while the maximum pressure rise rate, carbon monoxide and methane emissions reduced initially and then increased. When the first diesel injection ratio increased, combustion rate of natural gas–air mixture increased, methane and carbon monoxide emission decreased, and nitrogen oxide emission increased. When the first diesel injection timing was relatively rearward, the combustion process showed a distinct four-stage heat release characteristic. The proportion of premixed combustion of the first injected diesel and the duration of flame propagation of natural gas had considerable influence on methane emission. When the first diesel injection timing was relatively forward, the first injected diesel played a premixed role, and the start of combustion was controlled by the second injected diesel. A relatively high indicated thermal efficiency can be obtained under this injection strategy. The methane was mainly distributed in the cylinder wall and crevice area at exhaust valve opening due to the limitation of flame propagation under the multiple injection strategy.