Multiple Injection Strategies Research Articles

Modeling of the entire processes of diesel spray tip penetration including the start- and end-of-injection transients

The start-of-injection (SOI) and end-of-injection (EOI) transients are important for sprays with multiple-injection strategy. Owing to the change of needle position and sac pressure, the spray behaviors in the transient processes are significantly different from those in the quasi-steady stage. In this study, considering the sac pressurization processes during the SOI transients and effects of ''entrainment wave'' after the EOI, a theoretical zero-dimensional model for the entire development processes of the spray tip penetration (Stip) is summarized. Then, a high-speed CMOS camera and constant-volume chamber are employed to study the spray characteristics and verify the model. The model and experimental results clarify four key time points in the entire development processes of Stip: the sac pressurization time (tp), breakup time (tb), injection duration (ti) and two injection durations (2ti). Five stages can be divided according to these four time points: the acceleration stage (Stip proportion to t1.5), transition stage 1 (t1 or t0.75), quasi-steady stage (t0.5), transition stage 2 (t0.5) and decelerating stage ((t-ti) 0.25). Moreover, the newly developed model is compared with the Wakuri model, the Hiroyasu & Arai model, and the Naber & Siebers model. The results show that all the models can well predict Stip during the quasi-steady stage and transition stage 2 with the optimized model constants. While the other models overpredict Stip in the acceleration and decelerating stages, the newly developed model still works very well.

A comprehensive study on the effects of multiple injection strategies and exhaust gas recirculation on diesel engine characteristics that utilize waste high density polyethylene oil

ABSTRACT The present study utilized the catalytic pyrolysis method for extracting oil from waste high-density polyethylene (WHDPE) plastics. Experiments were carried out with D70H30 (diesel-70%, WHDPE oil-30%) blend under the influence of three start of pilot injection (SoPI) timings [45° before top dead center (bTDC), 50°bTDC, and 55°bTDC] and three pilot fuel injection quantity (PFIQ) (10%, 20%, and 30%) at the engine’s rated power output. Later, the impact of exhaust gas recirculation (EGR) (0%, 10%, and 20%) was studied with the optimum SoPI and PFIQ. Experimental results indicated that at SoPI timing of 55°bTDC and at PFIQ of 30%, the brake thermal efficiency (BTE) increased by 8.5%, nitrogen oxides (NOx) increased by 19.25%, while smoke, hydrocarbons (HC), and CO emission got lowered with baseline operation of the blend and found to be best among other modifications. In the next phase of the work, exhaust gas is recirculated at 10% and 20%. The results portray that inclusion of 10% EGR in the intake at SoPI 55°bTDC and at PFIQ 30% has shown 1.7% higher BTE, with 3.7% and 28.9% lower NOx and smoke emission compared to the single main injection of the blend. It is concluded that pilot injection strategy with 30% PFIQ and SoPI timing of 55°bTDC at 10% EGR rate can be adopted to utilize WHDPE oil/diesel in diesel engines effectively.

Hydraulic Interactions between Injection Events Using Multiple Injection Strategies and a Solenoid Diesel Injector

An experimental study was performed to explore the influence of dwell time on the hydraulic interactions between injection events using pilot injection strategy, split injection strategy, post injection strategy and a solenoid diesel injector. To do so, a sweep of dwell time from 0.55 up to 2 ms using all multiple injection strategies and levels of rail pressure, of 80, 100 and 120 MPa, and single level of back pressure, of 5 MPa, was performed. The hydraulic interactions between injection events were characterized through the second injection hydraulic delay and second injection mass in an injection discharge curve indicator equipped with all the components required for its operation and control. In order to define the operating conditions of the multiple injection strategies, to ensure the same injected fuel mass in all cases, the characteristic curves of injection rate for the solenoid diesel injector studied were obtained. The second injection hydraulic delay increases with dwell time values in the range of 0.55–0.9 ms for all multiple injection strategies and levels of rail pressure tested. Conversely, the second injection hydraulic delay decreases with dwell time values higher than 0.9 ms. Moreover, the second hydraulic delay depends mainly on the dwell time and not on the injected fuel mass during the first injection event. The second injection mass increases with dwell values less than 0.6 ms. By contrast, the second injection mass is not significantly affected by that of the first injection at a dwell time higher than 0.6 ms.

Numerical investigation of multiphase reactive processes using flamelet generated manifold approach and extended coherent flame combustion model

For the calculation of multiphase reactive processes in computational fluid dynamics (CFD), detailed chemical kinetics and simplified combustion models are commonly applied. An appropriate modelling approach to overcome the high computational demand of chemical kinetics is the flamelet generated manifold (FGM), which prescribe the calculation of chemical kinetics in preprocessor for the generation of the look-up databases that are used during CFD simulations with interpolation procedure. For the calculation of the chemistry kinetics in processor, combustion models are commonly applied, such as Three-zones extended coherent flame model (ECFM-3Z) that features calculation of flame speed in turbulent conditions. The primary goal of the research is to investigate and validate FGM and ECFM-3Z models on the multiphase reactive process inside a compression ignition engine for single and multiple injection strategies. Additionally, an overview of the modelling methodology and capability of FGM and ECFM-3Z models is presented, where the impact of their features is analysed on the results inside a compression ignition engine. For the numerical simulations, CFD code AVL FIRE™ was used, where the calculated results such as in-cylinder pressure, temperature, rate of heat release, and nitric oxide emissions are computed. The FGM modelling approach showed higher ignition delay compared to the ECFM-3Z model for single-injection strategy, which can be attributed to the pretabulated autoignition conditions in three zones of the ECFM-3Z model. For the multi-injection strategy, such an ignition delay difference between FGM and ECFM-3Z is not observed since the small amount of injected fuel in pilot injections tends to have quicker ignition, which then creates better conditions for combustion of the more significant amount of injected fuel in the main injection. The experimental nitric oxide emission trend is achieved with both combustion modelling approaches, where the CFD calculation time for cases with FGM is reduced approximately by half. In comparison against the experimental values, both FGM and ECFM-3Z combustion modelling approaches showed the capability of predicting the influence of fuel injection strategy on the combustion process in passenger car compression ignition engines.

G-equation based ignition model for direct injection spark ignition engines

To accurately model the Direct Injection Spark Ignition (DISI) combustion process, it is important to account for the effects of the spark energy discharge process. The proximity of the injected fuel spray and spark electrodes leads to steep gradients in local velocities and equivalence ratios, particularly under cold-start conditions when multiple injection strategies are employed. The variations in the local properties at the spark plug location play a significant role in the growth of the initial flame kernel established by the spark and its subsequent evolution into a turbulent flame. In the present work, an ignition model is presented that is compatible with the G-Equation combustion model, which responds to the effects of spark energy discharge and the associated plasma expansion effects. The model is referred to as the Plasma Velocity on G-surface (PVG) model, and it uses the G-surface to capture the early kernel growth. The model derives its theory from the Discrete Particle Ignition (DPIK) model, which accounts for the effects of electrode heat transfer, spark energy, and chemical heat release from the fuel on the early flame kernel growth. The local turbulent flame speed has been calculated based on the instantaneous location of the flame kernel on the Borghi-Peters regime diagram. The model has been validated against the experimental measurements given by Maly and Vogel,1 and the constant volume flame growth measurements provided by Nwagwe et al.2 Multi-cycle simulations were performed in CONVERGE3 using the PVG ignition model in combination with the G-Equation-based GLR4 model in a RANS framework to capture the combustion characteristics of a DISI engine. Good agreements with the experimental pressure trace and apparent heat-release rates were obtained. Additionally, the PVG ignition model was observed to substantially reduce the sensitivity of the default G-sourcing ignition method employed by CONVERGE.

On improving the controllability of low-temperature combustion by building two-stage sequential high-temperature reactions in an ethanol/diesel dual-fuel engine using multiple injections

Low-temperature combustion (LTC) has advantages in reducing emissions and improving efficiency, at the expense of hard controllability. To improve its controllability, this paper proposes a two-stage stratified compression ignition (TSCI) strategy, which aims to decouple ignition and the following combustion as two-stage sequential high-temperature reactions, and couple them to external events like multiple injections, supercharge, etc. A trace amount of high reactivity fuel (HRF) is injected near the top dead center (TDC) and auto-ignited, initiating the combustion process, which controls ignition. The highly premixed charge (HPC), whose equivalent ratio, temperature, reactivity can be tuned as needed, control the combustion course after ignition. Based on the TSCI concept, one demonstrative multiple-injection strategy is suggested and tested on a single-cylinder ethanol/diesel dual-fuel engine. It is concluded from the experimental results that the TSCI combustion process presents two-stage sequential high-temperature reactions, which is different from any other LTC strategies. This sequential combustion shows good controllability. Within a certain range, the ignition phase is directly and linearly related to the ignition-oriented injection (IOI) event. With the advance of IOI timing, the ignition is advanced consequently. Increasing IOI quantity has the same tendency. As for HPC, when HPC reactivity is increased, the maximum pressure raising rate (MPRR) is increased and the whole combustion process is more concentrated.

Lean-Stratified Combustion System with Miller Cycle for Downsized Boosted Application - Part I

<div class="section abstract"><div class="htmlview paragraph">Automotive manufacturers relentlessly explore engine technology combinations to achieve reduced fuel consumption under continued regulatory, societal and economic pressures. For example, technologies enabling advanced combustion modes, increased expansion to effective compression ratio, and reduced parasitics continue to be developed and integrated within conventional and hybrid propulsion strategies across the industry. A high-efficiency gasoline engine capable for use in conventional or hybrid electric vehicle platforms is highly desirable. This paper is the first to two papers describing the development of a combustion system combining lean-stratified combustion with Miller cycle for downsized boosted applications. The work was completed under a multi-year US DOE project. The goal was to define a light-duty engine package capable of achieving a 35% fuel economy improvement at US Tier 3 emission standards over a naturally aspirated stoichiometric baseline vehicle. A multi-mode combustion system was developed enabling highly efficient lean-stratified operation at light-load and stoichiometric Miller-cycle operation at mid- to high-loads. Some of the unique challenges in synergistically combining the two concepts are highlighted in this paper. A central direct-injection four-valve layout was designed with high-tumble ports and a bowl-in-piston capable of stable operation under highly dilute (lean plus EGR) mixtures when properly matched to fuel spray characteristics, a multiple-injection strategy, and a high-energy ignition system. Other challenges specific to meeting exhaust emissions requirements with a high-efficiency engine are also explored in this study. In this Part 1 of the paper, the single-cylinder combustion system design, analysis, and testing is described. Multi-cylinder engine system design, analysis and development is described in Part 2 of the paper [<span class="xref">1</span>].</div></div>

Experimental Analysis on the Effects of Multiple Injection Strategies on Pollutant Emissions, Combustion Noise, and Fuel Consumption in a Premixed Charge Compression Ignition Engine

Experimental Analysis on the Effects of Multiple Injection Strategies on Pollutant Emissions, Combustion Noise, and Fuel Consumption in a Premixed Charge Compression Ignition Engine

Experimental and modeling analysis of multiple-injection strategies with B20 operation in a CRDI engine

Biodiesel blend (B20) is the most widely adopted renewable alternative for diesel and their production feedstock varies significantly concerning geographic location and availability. Further, modern diesel vehicles involve an electronic injection system with varying multiple injection schedules for light and heavy-duty applications. Thus, testing a new feedstock with an optimum injection schedule is cumbersome and time-consuming. Thus, the current work involves a combined study of engine experiments with phenomenological combustion and emission modeling to ascertain the nature of B20 operation in an automotive LDD CRDI Engine. The twin-cylinder engine was experimentally tested with multiple- injection strategies, viz. single and triple with diesel and waste cooking biodiesel blend (B20) under three injection pressures. It is observed that the multiple-injection reduces nitric oxide (NO) and soot emissions simultaneously. The increase in NO emission with B20 can be mitigated to diesel level with the help of multiple-injection. The soot emission from B20 is significantly less than diesel at both single and triple injection cases. The model is validated with a wide range of experimental results and a parametric study has been carried out to explore the effect of operating parameters such as fuel quantity and the dwell period between the injection pulses for B20 fuel. The parametric investigations recommend a suitable pilot fuel quantity and longer dwell between the pilot and main injection for NO reduction, and a small quantity of post fuel and medium dwell between main and post-injection for achieving soot reduction without penalty on mean effective pressure.

Development of a Small-Bore Gasoline Direct-Injection Engine, and Enhancement of Its Performance Using Multiple-Injection Strategies

Development of a Small-Bore Gasoline Direct-Injection Engine, and Enhancement of Its Performance Using Multiple-Injection Strategies

The Role of Multiple Injections on Combustion in a Light-Duty PPC Engine

This paper presents a numerical investigation of the ignition and combustion process of a primary reference fuel in a partially premixed light-duty internal combustion (PPC) engine. Partially pre-mixed combustion is achieved by employing a multiple injection strategy with three short injection events of fuel pulses. The timing of the first two fuel pulses, 48 and 22 crank angle degrees before top dead center, are chosen with the purpose to stratify the fuel and air charge, whereas the third injection, at five crank angle degrees before top dead center, serves as an actuator of the main heat release. In addition to this baseline injection, three alternative injection strategies are studied, including a split-fuel two-injection strategy and modified triple-injection strategies. Large eddy simulations are employed utilizing a skeletal chemical kinetic mechanism for primary reference fuel capable of capturing the low-temperature ignition and the high temperature combustion. The large eddy simulation (LES) results are compared with experiments in an optical accessible engine. The results indicate that the first ignition sites are in the bowl region where the temperature is relatively higher, and the reaction fronts thereafter propagate in the swirl direction and towards the centerline of the cylinder. The charge from the first two injections initially undergoes low-temperature reactions and thereafter high-temperature reservoirs are formed in the bowl region. The main heat-release is initiated in the engine when the fuel from the third injection reaches the high-temperature reservoirs. Finally, the remaining fuel in the lean mixtures from the first two injections is oxidized. By variation of the injection strategy, two trends are identified: (1) by removing the second injection a higher intake temperature is required to enable the ignition of the charge, and (2) by retarding second injection, a longer ignition delay is identified. Both can be explained by the stratification of fuel and air mixture, and the resulting reactivity in various equivalence ratio and temperature ranges. The LES results reveal the details of the charge stratification and the subsequent heat release process. The present results indicate a rather high sensitivity of partially premixed combustion process to the injection strategies.

Modeling of diesel spray tip penetration during start-of-injection transients

Multiple-injection strategy that has been applied widely in diesel engines usually features a short duration for each injection pulse. As a result, the shortened injection makes the needle opening and closing transients increasingly important for spray in an injection event. Owing to the needle movement, the spray development during the transient processes is complex and quite different from the spray at the quasi-steady state. However, so far modeling of the spray development during the transient processes is far from adequate. Particularly, a theoretical zero-dimensional (0-D) spray tip penetration model considering the needle opening and sac pressurization processes as well as ambient and injection conditions during the start-of-injection (SOI) transients is still absent. In this paper, considering the sac pressurization processes, the 0-D model of spray tip penetration during the SOI transients is derived. Then, the model is validated against the experimental spray data using a long-distance microscope together with an ultrahigh speed CMOS camera. The model and experimental results show that the spray tip penetration shows a t3/2 dependence at the initial stage of injection rather than the t dependence suggested by Hiroyasu’s model. Later, the spray tip penetration shows a t3/4 dependence owing to the spray breakup, and a t1/2 dependence with the completion of sac pressurization. The models and analysis are believed to provide new insights into the transient spray behaviors and valuable reference for engineers and researchers who are considering the model-based development of next-generation diesel engines.

A Computational Investigation of the Impact of Multiple Injection Strategies on Combustion Efficiency in Diesel–Natural Gas Dual-Fuel Low-Temperature Combustion Engines

AbstractDual-fuel diesel–methane low-temperature combustion (LTC) has been investigated by various research groups, showing high potential for emissions reduction (especially oxides of nitrogen oxide (NOx) and particulate matter (PM)) without adversely affecting fuel conversion efficiency in comparison with conventional diesel combustion. However, when operated at low load conditions, dual-fuel LTC typically exhibits poor combustion efficiencies. This behavior is mainly due to low bulk gas temperatures under lean conditions, resulting in unacceptably high carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. A feasible and rather innovative solution may be to split the pilot injection of liquid fuel into two injection pulses, with the second pilot injection supporting CO and UHC oxidation once combustion is initiated by the first one. In this study, diesel–methane dual-fuel LTC is investigated numerically in a single-cylinder heavy-duty engine operating at 5 bar brake mean effective pressure (BMEP) at 85% and 75% percentage of energy substitution (PES) by methane (taken as a natural gas (NG) surrogate). A multidimensional model is first validated in comparison with the experimental data obtained on the same single-cylinder engine for early single pilot diesel injection at 310 crank angle degrees (CAD) and 500 bar rail pressure. With the single pilot injection case as baseline, the effects of multiple pilot injections and different rail pressures on combustion and emissions are investigated, again showing good agreement with the experimental data. Apparent heat release rate and cylinder pressure histories as well as combustion efficiency trends are correctly captured by the numerical model. Results prove that higher rail pressures yield reductions of HC and CO by 90% and 75%, respectively, at the expense of NOx emissions, which increase by ∼30% from baseline still remaining at very low level (under 1 g/kWh). Furthermore, it is shown that postinjection during the expansion stroke does not support the stable development of the combustion front as the combustion process is confined close to the diesel spray core.

Influence of aging of a diesel injector on multiple injection strategies

Multiple injection strategies have contributed to the improvement of thermal processes in Internal Combustion Engines. On this matter, the correct performance of the injector is a critical factor in the implementation of these techniques, as changes in the behavior of the injector could affect the injection development, altering the combustion process and heat transformation efficiency. Thus, the present study analyzes the development of multiple injection events in a diesel injector aged due to partial obstruction of the holes of the nozzle. To this end, a multi-hole piezoelectric injector was employed, in which the aging of the injector is evaluated through momentum flux measurements for each hole. Afterwards, rate of injection tests with pilot and post injection strategies are performed, and the results are compared to the injection events made by the same injector before aging. The results provided by the momentum flux experiments confirmed the partial obstruction of two holes. Furthermore, rate of injection comparisons showed that the injector had a lower steady-state rate of injection after aging and required a longer time to end the injection. These phenomena affected the multiple injection events, as the extended time required to end the injection reduced the hydraulic dwell time between pilot/post injection and the main injection. Furthermore, for short dwell times, this phenomenon led to the unification of the main and post injection, resulting in a large single injection. Hence, not only an increase in fuel consumption would appear, but the thermal benefits of implementing the post injection would be lost.

Analysis of the effects of multiple injection strategies with hydrogen on engine performance and emissions in diesel engine

In this study, firstly, the turbocharged, compression-ignition, light duty vehicle engine was loaded with a DC dynamometer. The real test engine was run at partial load (90%) and at different engine speeds with normal diesel fuel. In the second stage, a model engine was created and verified with the mixing control combustion (MCC) module suitable for hydrogen combustion using AVL BOOST simulation software with real test parameters such as engine performance and cylinder pressure values. At the last stage, multiple hydrogen injection strategies were applied in the simulation program using pure hydrogen as pilot and post fuel and diesel as the main fuel, and were examined numerically in terms of performance and emissions. The results showed that 2 pilot injections and 1 post-injection strategy reduced soot emissions more than 1 pilot injection strategy. However, NOx increased slightly in all three injection applications. In addition, a significant increase in engine power was observed.

Analysis of the Influence of Diesel Spray Injection on the Ignition and Soot Formation in Multiple Injection Strategy

Multiple injection strategies have increased their capabilities along with the evolution of injection system technologies up to the point that nowadays it is possible to inject eight different pulses, permitting to improve the engine performance, and consequently, emissions. The present work was realized for two simplified strategies: a pilot-main and a main-post, in order to analyze the influence of an auxiliary pulse on the main and otherwise, in reactive conditions for two pilot/post quantities and four hydraulic dwell times. The study was carried out by employing two optical techniques: diffused back-illumination with flame bandpass chemiluminescence for measuring soot, represented by soot-maps distribution, and single-pass schlieren for ignition delay (ID). Furthermore, a novel methodology for decoupling the start of combustion (SOC) of the second pulse was developed and successfully validated. From the ignition delay results, it was found for all test points that the pilot injection enhanced conditions, which promote a faster ignition of the main pulse, also at higher chamber temperatures, all conditions presented a separate combustion event for each injection. In emission terms, soot increased in the pilot-main strategies compared to its single injection case, as well as, in conditions that promote faster-premixed combustion.

Study of diesel fuel multiple injection characteristics using shadow-graphic imaging technique with CRDI system in constant volume chamber

The behaviour of injection spray characteristics is an essential part to better understand the combustion. Thus, to address the hurdles faced during physical measurement of spray structural properties an efficient visual technique is required. With the point of promoting the estimation of injected spray split-positional characterisation along with fuel injection time duration is being performed on multiple injection strategy with diesel as working fluid. Further, through visual examination characteristics of spray tip penetration along with the motion of the injected spray is performed. A visualisation set called shadowgraph optical technique is implemented to capture the injected fluid spray inside the combustion chamber by common rail direct injection. The developed MATLAB algorithm is validated from the obtained results, the effective estimation of spray intensity between 1st spray injection and 2nd spray injection supports in a way to choose the appropriate dwell time between successive injections which avoid the formation of the pocketed fuel-rich region. From the results of the case example, observed that 1st spray injection duration take persists throughout for 1680 µs, dwell time duration is 67.2 µs and 2nd spray injection duration occurs for 1276.8 µs. So, the choice of 2nd spray injection after 1680 µs from the injection point of 1st spray is advisable. Further, fuel spray tip penetration is observed as 50.6122 mm length and cone angle as 152°, examined and visualised during the operation. The developed MATLAB algorithm for an optical spray visualization technique has an efficient impact in determining the characteristics of fuel spray injected throughout the multiple injection process.

Effect of multiple fuel injection strategies on mixture formation and combustion in a hydrogen-fueled rotary range extender for battery electric vehicles

The hydrogen-fueled range extender based on the rotary engine is a promising solution for battery electric vehicles due to key advantages such as: high efficiency, small packaging dimensions and low weight within the framework of the near zero-emission concept. Although rotary engine has been examined over the past years, the detailed knowledge of hydrogen combustion in the rotary engine with direct injection system has not been investigated properly. In this paper, the rotary range extender was numerically studied with a focus on the influence of the direct multiple injection strategies on hydrogen distribution and combustion. The result demonstrates that due to large flame speed and diffusion length the engines fueled by pure hydrogen differ significantly from the engines with conventional fuel. The process is characterized by the weak influence of turbulence on the flame during almost the whole combustion stroke except for the late stages when 70% of the fuel is already burnt. Hence the difference in the injection strategies lead to different local hydrogen distribution that has effects on combustion rate and performance characteristics significantly. Fuel stratification leads to the formation of subregions with various hydrogen concentration. The lean mixture cannot provide enough high temperature, whereas the rich mixture is characterized by a lack of oxygen. The total NOx formation can be twice lower in comparison with premixed combustion at the same averaged equivalence ratio. The direct multiple injection strategy allows the use of a higher averaged equivalence ratio up to 0.8 which results in larger power density in combination with low NOx emission.

Low Temperature Combustion with Multiple Injection Strategies in Single Cylinder Diesel Engine

Low-temperature combustion(LTC) with multiple injection strategies is a recent trend for NOx and soot reduction in single-cylinder diesel engines. This paper presents a technical study of past research carried out on multiple injections, which are pilot I and pilot II injection before main injection, to decrease engine soot to meet emission legislation while upholding efficiency and decrease or eliminate exhaust after treatment. Previous research indicates that extending ignition lag to enhance the proper premixing, and controlling temperature of combustion to optimal level using Exhaust Gas Recirculation, have been accepted as an important aspect to attain low temperature combustion. In this paper, we first discuss the effect pilot I injection and pilot II injection strategy through varied injection quantity and time range. Thereafter, we briefly review how pilot II injection provides better results compared with the pilot I injection, which is by reason of better premixing, improves the turbulent effect and lowers the emission. Next, we provide a broad overview of the collected works on the effect of injection pressure, temperature and rate of exhaust gas recirculation on engine emissions. We conclude by identifying a few dependencies of engine parameters in low-temperature combustion by multiple injections so as to reduce the engine emissions.

Study of evaporative diesel spray interaction in multiple injections using optical diagnostics

Internal combustion engines have witnessed an ever increasing stringency in emission limits and fuel economy regulations that has continuously provoked researchers to develop complex strategies that enables engines to cope with these standards. Optical techniques have been a viable method in the study of thermal processes occurring inside internal combustion engines and provides researchers with a solid understanding of the heat and mass transfer taking place. In particular, the current study utilizes two optical techniques, diffused back illumination and schlieren imaging, to visualize the spray behavior in multiple injection strategies of evaporative diesel sprays. A novel method has been developed in order to couple the two optical techniques to visualize both liquid and vapor phases of either pilot-main and main-post injections. The influence of the auxiliary injections on the main, and vice versa, in terms of spray segmentation and spray development has been studied for two different pilot/post quantities and four hydraulic dwell times under two different chamber conditions. The spray development displayed no effect of pilot quantity and dwell time on the liquid length of the second injection. On the other hand, a more pronoun effect on the vapor phase penetration and spreading angle was evidenced by the pilot injection where the main injection has penetrated farther with a higher spreading angle as compared to the case with a single injection event. The understanding of multiple injection is thus fundamental for the improvement of thermal processes in Internal Combustion Engines.