Main Injection Research Articles

High-Strain-Induced Local Modification of the Electronic Properties of VO2 Thin Films.

Vanadium dioxide (VO2) is a popular candidate for electronic and optical switching applications due to its well-known semiconductor-metal transition. Its study is notoriously challenging due to the interplay of long- and short-range elastic distortions, as well as the symmetry change and the electronic structure changes. The inherent coupling of lattice and electronic degrees of freedom opens the avenue toward mechanical actuation of single domains. In this work, we show that we can manipulate and monitor the reversible semiconductor-to-metal transition of VO2 while applying a controlled amount of mechanical pressure by a nanosized metallic probe using an atomic force microscope. At a critical pressure, we can reversibly actuate the phase transition with a large modulation of the conductivity. Direct tunneling through the VO2-metal contact is observed as the main charge carrier injection mechanism before and after the phase transition of VO2. The tunneling barrier is formed by a very thin but persistently insulating surface layer of the VO2. The necessary pressure to induce the transition decreases with temperature. In addition, we measured the phase coexistence line in a hitherto unexplored regime. Our study provides valuable information on pressure-induced electronic modifications of the VO2 properties, as well as on nanoscale metal-oxide contacts, which can help in the future design of oxide electronics.

Fabric Insert Injection Molding for the Preparation of Ultra-High Molecular Weight Polyethylene/High-Density Polyethylene Two-Component Self-Reinforced Composites.

The fabric insert injection molding approach can be applied to produce easily recyclable self-reinforced polymer composites (SrCs) whose reinforcement and matrix are from the same polymer. However, the mechanical properties of the SrCs are usually limited due to the poor impregnation of the inserted fabric. In this work, the ultra-high molecular weight polyethylene (UHMWPE) fabrics were used as the insert, and the high-density polyethylene (HDPE) melt was injected to fill the mold cavity and impregnate the fabrics. The UHMWPE/HDPE two-component SrCs were prepared. The large difference of melting temperatures between UHMWPE and HDPE can establish a wide processing temperature window, and thus the impregnation of the fabric can be improved by increasing temperature. The tensile strength and modulus of the UHMWPE/HDPE SrCs were up to 148 and 1132 MPa, respectively. The peel strength could be up to 35.2 N/cm. The influences of four main injection molding parameters, including the injection temperature, injection pressure/packing pressure, injection velocity, and packing time, were investigated. The temperature, pressure, viscosity, and density of the matrix in the mold cavity were calculated by the numerical simulation to indicate the impregnation process during the fabric insert injection molding process.

Investigating a deterministic yet computationally cheap combustion parameter for model predictive control of a CNG-diesel RCCI engine

This study investigates the changing deterministic features of the cycle-resolved location of maximum pressure and its correlation with combustion phasing for dynamical transitions in the combustion of a CNG-Diesel RCCI engine. The investigation is performed using nonlinear dynamical and chaotic methods such as return maps, recurrence, and cross recurrence plots. The experiments are performed on a single-cylinder automotive engine operated in RCCI mode with the aid of the development ECU. The experiments are conducted by running the engine at a fixed engine speed of 1500 rpm and a load of 3 bar BMEP. Diesel fuel is injected directly into the cylinder by following a double injection strategy using an equal amount of fuel in both the pilot and main injections. The effect of the start of main injection timing of diesel on combustion dynamics is investigated at two different masses of CNG. The predominance of deterministic periodic features is discovered in the cycle-resolved dynamics of the engine combustion during the RCCI regime. Results show that with advancement in diesel injection timing, the mode of combustion shifts from conventional dual fuel to RCCI, and this shift is coupled to the onset of noisy periodic-2 bifurcations., The periodic-2 behavior even transforms to periodic-3 and 4 with an increasing advancement in diesel injection timing for engines operating with a higher CNG mass. For most of the operating conditions, the deterministic features in the location of maximum pressure are comparable with that of combustion phasing. Recurrence and cross recurrence plots-based methodology advocates for the existence of strong correlations or at least a phase synchronization between the location of maximum pressure and combustion phasing when the engine operates in the RCCI regime, irrespective of diesel injection timing and amount of port-injected CNG fuel. The presence of similar deterministic features in the location of maximum pressure and combustion phasing and a strong relationship between these two at intermediate diesel injection timings in the RCCI regime for both the CNG masses makes this regime most suitable for using the location of maximum pressure as a feedback/controlled parameter for model predictive control of the engine.

Utilization of Hydrotreated Vegetable Oil (HVO) in a Euro 6 Dual-Loop EGR Diesel Engine: Behavior as a Drop-In Fuel and Potentialities along Calibration Parameter Sweeps

This study examines the effects on combustion, engine performance and exhaust pollutant emissions of a modern Euro 6, dual-loop EGR, compression ignition engine running on regular EN590-compliant diesel and hydrotreated vegetable oil (HVO). First, the potential of HVO as a “drop-in” fuel, i.e., without changes to the original, baseline diesel-oriented calibration, was highlighted and compared to regular diesel results. This showed how the use of HVO can reduce engine-out emissions of soot (by up to 67%), HC and CO (by up to 40%), while NOx levels remain relatively unchanged. Fuel consumption was also reduced, by about 3%, and slightly lower combustion noise levels were detected, too. HVO has a lower viscosity and a higher cetane number than diesel. Since these parameters have a significant impact on mixture formation and the subsequent combustion process, an engine pre-calibrated for regular diesel fuel could not fully exploit the potential of another sustainable fuel. Therefore, the effects of the most influential calibration parameters available on the tested engine platform, i.e., high-pressure and low-pressure EGR, fuel injection pressure, main injection timing, pilot quantity and dwell-time, were analyzed along single-parameter sweeps. The substantial reduction in engine-out soot, HC and CO levels brought about by HVO could give the possibility to implement additional measures to limit NOx emissions, combustion noise and/or fuel consumption compared to diesel. For example, higher proportion of LP EGR and/or smaller pilot quantity could be exploited with HVO, at low load, to reduce NOx emissions to a greater extent than diesel, without incurring penalties in terms of incomplete combustion species. Conversely, at higher load, delayed main injection timings and reduced rail pressure could reduce combustion noise without exceeding soot levels of the baseline diesel case.

Effect of injection strategy optimization on PCCI combustion and emissions under engine speed extension in a heavy-duty diesel engine

To mitigate the consequent emissions of greenhouse gases and to conform to increasingly strict vehicle emission requirements, experiments and numerical simulation were used to study effects of multiple injection strategy on premixed charge compression ignition (PCCI) combustion and emissions under speed extension in a heavy-duty diesel engine fueled with diesel. As the speed increases, the injection duration is prolonged, the injection rate is decreased, the fuel-oxygen mixing degree is decreased. In order to enhance fuel-oxygen mixing, the injection timing of single injection should firstly be optimized to fully utilize the shape of the chamber. Compared with single injection, the double injections can increase the mixing time, the optimized multiple injections can further increase the mixing time, making the premixing more sufficient and the combustion more complete. Compared with double injections, the optimized multiple injection strategy used in this paper adds a short pulse pilot injection before the main injection, which prolongs the duration of turbulent motion in the cylinder, and enhances the mixing rate of the main injection fuel and air. Results reveals that for single injection with injection timing of −15°CA ATDC, at low speed, through optimizing the injection strategy, the NOx and soot emissions are reduced by 38.5% and one order of magnitude, respectively, and the gross indicated thermal efficiency (ITEg) is increased by 8.66%; at medium speed, by optimizing the injection strategy, the NOx and soot emissions are reduced by 59.3% and 70.4%, respectively, and the ITEg is increased slightly by 0.33%; at high speed, by optimizing the injection strategy, the soot emission is decreased significantly, the NOx emissions and the ITEg are increased slightly. It was found that with the increase of speed, the effect of multiple injection strategy on the ITEg and emissions is gradually increased, and the optimization effect of multiple injection strategy is more obvious than that of low speed.

Three‐dimensional numerical simulation on fiber orientation of short‐glass‐fiber‐reinforced polypropylene composite thin‐wall injection‐molded parts simultaneously accounting for wall slip effect and pressure dependence of viscosity

AbstractOn account of the inherent features of the thin‐wall injection molding process, a three‐dimensional numerical model, which accounts for wall slip effect and pressure dependence of viscosity (PDoV), was proposed for a more accurate simulation of the fiber orientation in thin‐wall injection‐molded parts of short‐glass‐fiber‐reinforced polymer composites (SGFRPC). First, the fiber orientation was simulated using the three‐dimensional and mid‐plane models, respectively. The comparison between the simulated and experimental results verifies that the three‐dimensional numerical results were in better agreement with the experimental measurements. Secondly, the influences of wall slip effect and PDoV on fiber orientation in thin‐wall injection‐molded parts of SGFRPC were analyzed based on the three‐dimensional numerical model. The results show that the three‐dimensional numerical simulation simultaneously accounting for wall slip effect and PDoV can better predict the fiber orientation in thin‐wall injection‐molded parts of SGFRPC, suggesting the validation of the proposed model. Finally, five main processing parameters, that is, injection rate, melt temperature, mold temperature, packing pressure, and packing time, were also studied in terms of their influences on the fiber orientation in thin‐wall injection‐molded parts of SGFRPC.

Combustion and emission characteristics of diesel engine fueled with diesel/cyclohexanol blend fuels under different exhaust gas recirculation ratios and injection timings

Cyclohexanol is obtained from abundant lignocellulosic biomass sources at low cost, and it is a promising alternative fuel for diesel engines. In this study, cyclohexanol was blended with diesel at various volume ratios and the mixtures were denoted as D100 (100 % diesel + 0 % cyclohexanol), D90CH10 (90 % diesel + 10 % cyclohexanol), and D80CH20 (80 % diesel + 20 % cyclohexanol), respectively. Subsequently, the effects of exhaust gas recirculation and pilot plus main injections at various pilot injection timings on the combustion and emissions of the diesel engine fueled with various mixtures were evaluated. The results demonstrated that diesel/cyclohexanol blends had a longer ignition delay, but shorter combustion duration. D80CH20 had the highest oxygen content, peak combustion temperature (PCT), and peak heat release rate (PHRR) at medium and high loads. Cyclohexanol blending with diesel significantly decreased the particulate number (PN) and volume concentrations at the expense of higher NOx emissions. Advancing the pilot injection timing prolonged the ignition delay and combustion duration, and increased the PCT and PHRR. Therefore, it emitted higher NOx emissions, but lower PN emissions. D80CH20 with 8 % EGR can simultaneously reduce the PN and NOx emissions at medium and high loads.

Numerical analysis of diesel injection strategies on emissions and performance in CH4/diesel powered RCCI diesel engine with high ratio EGR

In this study, the effects of intake port injection of methane and direct of injection diesel on emissions and the combustion of a light-duty RCCI engine were numerically researched. In this way, AVL Boost software was used for 1-dimensional simulation of the combustion process and emission estimation. Higher octane number methane gas was mixed with air from the intake port, while lower octane number diesel fuel was injected directly into the combustion chamber during the compression stroke. Methane gas was injected at a rate of 65% and diesel fuel at a rate of 35%. The diesel injected directly into the combustion chamber was sprayed at a rate of 5% between 0 and 35 °CA with 8 different injection timings after the main injection. In the model engine, 50% high EGR rate was applied in all combustion modes. The results showed that these parameters have significant effects on performance and emissions. The results in summary; NOx emission reduced at all engine speeds with delayed diesel post-injection timing. The maximum drop of NOx emission was 57.34% with Post15. Although the addition of methane slightly increased the soot emission, it was significantly reduced by the simultaneous addition of methane and application of post-injection strategies of diesel fuel. The soot emission was reduced by 58.85% with the Post35 injection strategy.

Influence of a Novel Mixed Dialkyl Oxalate on the Combustion and Emission Characteristics of a Diesel Engine.

Oxygen-containing alternative fuels have excellent potential to improve diesel fuel economy and reduce particulate matter (PM) emissions. In this study, a novel mixed dialkyl oxalate (mDAO) as an additive was applied to substitute conventional diesel to investigate the effects of mDAO on the combustion and emission characteristics of a high-pressure common-rail diesel engine. The research conducted suggested that the peak pressure rise rate in the main injection stage and the peak in-cylinder pressure presented the rising tendency with the increased mass fraction of mDAO at most test conditions. With the addition of mDAO, the in-cylinder temperature (T) and brake thermal efficiency (BTE) were higher than that of pure diesel. When the mass fraction of mDAO in the mDAO/diesel blend was 30%, the improvement of BTE was most obvious. The ignition delay was prolonged as the mass fraction of mDAO was increased due to the lower cetane number of the mDAO. In addition, adding mDAO into diesel had an effective impact on the reduction of PM emissions, while the nitrogen oxide (NOx) emissions deteriorated. These results indicate that mDAO is a great potential diesel alternative fuel.

Development of a Control-Oriented Ignition Delay Model for GCI Combustion

Increasingly stringent pollutant emission limits and CO2 reduction policies are forcing the automotive industry toward cleaner and decarbonized mobility. The goal is to achieve carbon neutrality within 2050 and limit global warming to 2 °C (possibly 1.5 °C) with respect to pre-industrial levels as stated in both the European Green Deal and the Paris Agreement and further reiterated at the COP26. With the aim of simultaneously reducing both pollutants and CO2 emissions, a large amount of research is currently carried out on low-temperature highly efficient combustions (LTC). Among these advanced combustions, one of the most promising is Gasoline Compression Ignition (GCI), based on the spontaneous ignition of a gasoline-like fuel. Nevertheless, despite GCI proving to be effective in reducing both pollutants and CO2 emissions, GCI combustion controllability represents the main challenge that hinders the diffusion of this methodology for transportation. Several works in the literature demonstrated that to properly control GCI combustion, a multiple injections strategy is needed. The rise of pressure and temperature generated by the spontaneous ignition of small amounts of early-injected fuel reduces the ignition delay of the following main injection, responsible for the torque production of the engine. Since the combustion of the pre-injections is chemically driven, the ignition delay might be strongly affected by a slight variation in the engine control parameters and, consequently, lead to misfire or knocking. The goal of this work was to develop a control-oriented ignition delay model suitable to improve the GCI combustion stability through the proper management of the pilot injections. After a thorough analysis of the quantities affecting the ignition delay, this quantity was modeled as a function of both a thermodynamic and a chemical–physical index. The comparison between the measured and modeled ignition delay shows an accuracy compatible with the requirements for control purposes (the average root mean squared error between the measured and estimated start of combustion is close to 1.3 deg), over a wide range of operating conditions. As a result, the presented approach proved to be appropriate for the development of a model-based feed-forward contribution for a closed-loop combustion control strategy.

Effects of different main injection timings and injection pressures on combustion and emissions of diesel-THF-ethanol blended fuel

ABSTRACT The effects of additives tetrahydrofuran (THF) and ethanol on combustion, performance and emissions were researched on a six-cylinder turbocharged diesel engine with varying injection strategies. Four fuels were tested, i.e. pure diesel, T15E0, T5E10, and T5E20. Under low load, the maximum cylinder pressure of blended fuel decreased and that of T15E0 decreased with the maximum decrease of 3.35%, from 6.56 MPa to 6.34 MPa. The maximum cylinder pressure was also reduced by 4.24% at most under high load, from 9.90 MPa to 9.48 MPa. With the addition of tetrahydrofuran, the brake specific fuel consumption (BSFC) increased, and the brake thermal efficiency (BTE) decreased. In comparison to pure diesel, the addition of 20% ethanol increased BTE from 35.4% to 35.9%, which was a 1.34% rise. For various injection strategies, the optimized soot emissions of T5E20 decreased by 66.94%, from 0.00289 g/kW·h to 0.00096 g/kW·h, while the maximum increase ratio of NOx emissions was 9.67%, from 9.88 g/kW·h to 10.84 g/kW·h. T5E20 has the potential to increase BTE while decreasing NOx and soot emissions concurrently. The results indicate that tetrahydrofuran is a good cosolvent for diesel-ethanol blended fuel, and ethanol exhibits good performance as the principal component of the blended fuel.

Trade-off characteristic between soot and oxides of nitrogen emission with pre-injected diesel and biodiesel in a SICI-CIDI engine

In this work, SICI mode (Split Injection Compression Ignition) was tested, using diesel as a split injected fuel along with the diesel and biodiesel main injection with various split injected ratios of 0.20, 0.40 and 0.60. Re-circulated Exhaust Gas has been used to analyse the variation in performance and emission, with the exhaust gas rate was varied from 10% to 30% to control nitrogen di oxide and nitrous oxide emissions. The experimental results compared with conventional diesel injection was done in the main chamber. It has been established that hydrocarbons, soot emissions, and carbon monoxide increase as per the experiments carried out on a CIDI engine. With up to 20% recirculated exhaust gas, soot emission decreases and increases when recirculated exhaust gas was increased beyond 20%. So, 20% recirculated exhaust gas would be the optimum use for SICI mode (Split Injection Compression Ignition) with a Split Injected ratio of 0.20%. Compared to CIDI mode, brake thermal efficiency has been slightly decreased. Consequential reduction in NOx can be achieved with the SICI combustion mode due to the lean operation.

Prediction of split injection strategy assisted diesel engine combustion, performance and emission characteristics fuelled waste frying oil methyl ester through central composite design

The objective of this study is to use response surface methodology to forecast the performance, combustion, and emission characteristics of an advanced injection strategy-assisted diesel engine running on waste frying oil methyl ester. The experiment was carried out on a diesel engine using a high-pressure fuel injection system. The main injection timing ranges varied from 16 to 24 °CA bTDC, whereas the post-injection ranges from −6 °CA bTDC to 6 °CA aTDC. The injection quantity for the main and post injections quantity varied from 70 % to 90 %, 10 % to 30 %, and the injection pressure is set at 500 bar. Experiments were carried out using a design matrix developed by the design of experiments. At 100 % load, B100-90 %-10 % obtained the highest BTE of 33.87 % and the lowest fuel consumption of 0.268 kg/kW-hr. At the main injection timing of 22 °CA and post-injection timing of −4 °CA, D100-80 %-20 % achieved the lowest unburned hydrocarbon, Smoke emission of 13 ppm, and 1.613 FSN respectively. The point prediction approach was used to forecast the combustion and emission parameters of a diesel engine, and the predicted results were in good agreement with the experimental results. Furthermore, when compared to advance injection timing for biodiesel fuel, retarded injection timing reduces nitric oxide emission. The Split injection strategy is one of the most effective techniques to reduce soot and NO × emissions while maintaining diesel engine efficiency.

Effects of EGR combined with DOC on emission characteristics of a two-stage injected Fischer-Tropsch diesel/methanol dual-fuel engine

Fischer-Tropsch (F-T) diesel and methanol are widely regarded as promising clean alternative fuels for engines. The emergence of reactivity controlled compression ignition (RCCI) combustion mode provides new approaches to the application of F-T diesel and methanol in diesel engines, but there is a pressing need to further reduce engine emissions. To this end, a dual-fuel engine test bench was built based on a high-pressure common rail diesel engine with a methanol injection system at the intake manifold combined with a two-stage in-cylinder direct injection (pre-injection + main injection) F-T diesel. The combined effects of methanol substitution ratio (MSR), exhaust gas recirculation (EGR) and diesel oxidation catalyst (DOC) on the combustion and emission characteristics of the dual-fuel engine was investigated at 2000 rpm and 75 % load. The results show that EGR improves the combustion characteristics of the F-T diesel/methanol dual-fuel engine while adding a DOC significantly reduces engine gaseous emissions. However, as the MSR and EGR rate increase, NOx emissions decrease, but other emissions increase. NOx emissions were reduced by 73 % compared to the original engine emissions for an MSR of 30 % and an EGR rate of 15 % without a DOC. When the MSR is 0 %, the DOC promotes the conversion of NO to NO2. While, when the MSR greater than 0, the DOC promotes the conversion of NO2 to NO. When equipped with a DOC, CO, NO, NO2, NOx, MeOH, and HCHO emissions decrease as the EGR rate increases, with the reduction of CO and MeOH emissions being greater than 99.5 % and 93 %, respectively, and the maximum conversion efficiency for HCHO emissions being 82 %. The present study showcases the key challenges as well as advantages in the use of EGR combined with a DOC assisting the application of coal-based alternative fuels in dual-fuel engines.

Application of pilot injection strategies for enhanced ignition and combustion of a low reactivity fuel in a compression-ignition engine

• Pilot injection can enhance combustion of a low reactivity fuel. • Pilot mixtures merging with main jet is a cause for studied mixture conditions. • Earlier pilot injection achieves enhanced reaction for studied mixture conditions. • Higher pilot proportion and shorter pilot-main dwell have higher effects. • HCHO formation is higher and its consumption to form OH is increased. The impact of pilot injection on ignition and combustion of a low-reactivity fuel is systematically investigated in an optically accessible light-duty compression-ignition engine. The role of key pilot-main injection control parameters, including the pilot injection timing, proportion and pilot-main injection dwell time, is found through line-of-sight integrated high-speed imaging of cool-flame and OH* chemiluminescence signals as well as planar laser-induced fluorescence imaging of formaldehyde (HCHO-PLIF) and hydroxyl (OH-PLIF). This suite of diagnostics enables visualisation of low-temperature reaction and high-temperature reaction during the extended ignition delay period of a selected low reactivity fuel with only 30 cetane number. The results show significant combustion enhancement associated with the pilot-main injection strategy for all injection timings tested. The enhanced ignition is most effective in the case of retarded injection timings with almost misfiring single injection operation recovered for stable and strong combustion due to the pilot mixture merged with the main fuel jet. This enhancement effect is further promoted when the proportion of pilot injection mass to the total fuel mass is increased or the dwell time between the pilot and main injection is decreased as the pilot mixture interaction with the main fuel jet is enhanced. Compared to the single injection, measured HCHO-PLIF signals are higher and OH-PLIF signals develop at a higher rate due to the pilot injection, indicating the pilot mixture addition enhanced both the low-temperature reaction and high-temperature reaction of the tested low-reactivity fuel.

ASSESSMENT OF THE QUADRUPLE INJECTION STRATEGY OVER TRIPLE INJECTIONS TO IMPROVE EMISSIONS, PERFORMANCE AND NOISE OF THE AUTOMOTIVE DIESEL ENGINE

The present study aims at investigating effectiveness of the quadruple (early-pilot-main-after [epMa]) injection strategy over three different triple [early-main-after (eMa), early-pilot-main (epM) and pilot-main-after (pMa)] injection scheduling in terms of emissions, performance [brake specific fuel consumption (BSFC), torque, brake thermal efficiency (BTE) and fuel economy] and noise. The experimentation was carried out on a heavy-duty BS-IV diesel engine with 45% EGR fraction and fixed main injection (Crank-angle) scheduling at eight different RPMs and three loads of engine (20%, 60% and 100%) using design of experiments(DOE). This comprehensive study showed that the quadruple injection strategy provides optimum results in both performance and emissions compared to the promising three triple injection strategy. The quadruple injection strategy exhibits the best BTE at all operating conditions and best BSFC at medium to high-speed zone around 0.5–1% inline to reduce combustion noise (CN) level, especially at low speeds and low to medium load of 0.2–2.2 dBA. Among triple injections, the pMa shows the best performance in BSFC, BTE, smoke and THC emissions. The epM is the best in the CO emissions and torque performance in the low-speed zone. Smoke value is marginally higher for the epMa at low to medium speed than the pMa, although average smoke emissions were the best. Taken together, the overall PM emission level was marginally better than Triple Injections, due to the impact of double pilots in combination with post-injection. In addition, NOx emissions were improved (around 3–6%) significantly with quadruple than with triple injections. The epMa injection scheduling also showed improvement in constant speed fuel economy and in pass-by-noise at the vehicle.

Optical and computational investigations of the effect of Spray-Swirl interactions on autoignition and soot formation in a compression ignition engine fuelled by Diesel, dieseline and diesohol

Diesel engine injection strategy plays a crucial role in fuel–air mixing and consequent soot formation, requiring optimisation. Fuel properties affect the combustion characteristics of the engine significantly. In this study, the fundamental mechanisms of pilot-main injection interactions and the effects of fuel properties have been investigated using a combined approach of optical diagnostics in an optical engine and computational fluid dynamics (CFD) tools. A single-cylinder optical research engine (SCORE) with a cylindrical piston bowl was used for the optical engine investigations. Simulations were carried out using a re-entrant piston geometry model. Reynolds-Averaged Navier-Stokes (RANS) based Re-Normalization Group (RNG) k-ε model was adopted and solved using CONVERGE CFD solver. SAGE detailed chemistry solver was used for the calculations of combustion kinetics. The adaptive mesh refinement (AMR) strategy was used for improved grid resolution. The investigation results highlighted a striking difference between the combustion mechanisms of the pilot injection and the main injection. The pilot-main injection interactions became crucial for igniting the main fuel spray. The swirl intensity was dominant in the pilot-main injection interactions and the combustion initiation. The impinging spray jet and swirl interactions improved the radial mixing and reduced the soot in the up-swirl direction. Dieseline (a blend of diesel and gasoline) and diesohol (a blend of diesel and alcohol) resulted in lower soot formation than baseline diesel. This study demonstrated that in-cylinder swirl and oxygen concentration could be optimised to simultaneously reduce oxides of nitrogen (NOx) and soot emissions using oxygenated fuels.

Optical characterization of stratified-premixed natural gas direct-injection combustion regimes.

Gaseous fuels for heavy-duty internal combustion engines provide inherent advantages for reducing CO2, particulate matter (PM), and NOX emissions. Pilot-ignited direct-injected NG (PIDING) combustion uses a small pilot injection of diesel to ignite a late-cycle main direct injection of NG, resulting in significant reduction of unburned CH4 emissions relative to port-injected NG. Previous works have identified NG premixing as a critical parameter establishing indicated efficiency and emissions performance. To this end, a recent experimental investigation using a metal engine identified six general regimes of PIDING heat release and emissions behavior arising from variation of NG stratification through control of relative injection timing (RIT) of the NG with respect to the pilot diesel. The objective of the current work is to provide comprehensive description of in-cylinder fuel mixing of direct injected gaseous fuel and its impacts on combustion and pollutant formation processes for stratified PIDING combustion. In-cylinder imaging of OH*-chemiluminescence (OH*-CL) and PM (700 nm), and measurement of local concentration of fuel is considered for 11 different , representing 5 regimes of stratified PIDING combustion (performed with MPa and ). The magnitude and cyclic variability of premixed fuel concentration near the bowl wall provides direct experimental validation of thermodynamic metrics ( , , ) that describe the fuel-air mixture state of all 5 regimes of PIDING combustion. The local fuel concentration develops non-monotonically and is a function of RIT. High indicated efficiency and low CH4 emissions previously observed for stratified-premixed PIDING combustion in previous (non-optical) investigations are due to: (i) very rapid reaction zone growth ( m/s) and (ii) more distributed early reaction zones when overlapping pilot and NG injections cause partial pilot quenching. These results connect and extend the findings of previous investigations and guide the future strategic implementation of NG stratification for improved combustion and emissions performance.

Influence of different biodiesel fuels on the PCCI-DI combustion concept for constant speed genset application

Homogenous charge compression ignition (HCCI) is a technology for concurrently reducing nitrogen oxides (NOx) and particulate matters (PM) emissions. Since, the pure HCCI lags in control over combustion phasing, Pre-mixed charge compression ignition (PCCI) method is proposed. To achieve partial homogeneity in PCCI combustion, the air is pre-injected with fuel. The main injection is required for the combination to take place. This paper investigates the impact of using the varying percentages and types of bio-diesels for the constant speed genset application engine. The paper first discus the effect of various ratios of diesel and biodiesel mixtures on the performance parameters like engine power, specific fuel consumption (sfc) and the break thermal efficiency. These effects are caused by the combustion happening inside the combustion chamber which can be seen in pressure, temperature and heat release curves. The result of the simulation finally discusses the formation of NOx and PM emissions during the combustion. These results also provide guidelines for actual testing of the engine with bio-diesel.

Numerical study on the effect of multiple injection strategies on ignition processes for low-temperature diesel spray

The multiple-injection strategies can significantly improve the diesel engine startability at low-temperature conditions, but the processes are extremely complex due to the effect of various factors simultaneously. To find out how the pilot injection affects the main injection, the spray and ignition with different injection strategies at low temperatures, and the effect of the interaction of the pilot and main injections on mixing and ignition are studied numerically. The results show that the main injection fuel can catch up with the pilot injection which has been pre-heated, making the peripheral fuel of the main injection has a higher temperature and equivalence ratio compared to the single injection, which can accelerate the chemical reaction process and thus shorten the ignition delay. The products of the pre-reacted pilot fuel are mixed with the peripheral fuel of the main injection and affect the reaction process. The pre-injected fuel can promote the combustion and shorten the ignition delay of the main injection fuel because the remaining species of pre-injected fuel can make n-dodecane dehydrogenated with the intermediate products such as OH in preference to O2. However, mixing the injections too late prevents the pre-injected fuel from promoting the combustion of the main injection. The concentration of CH2O increases rapidly during the first heat release, and the species at this moment significantly inhibit the combustion of the new fuel.