Effect Of Injection Timing Research Articles

Experimental Study on the Effect of Injection Timing on a Dual Fuel Diesel Engine Operated With Biogas Derived From Food Waste

Abstract The present work emphasizes the effects of injection timing on the characteristics of a 5.2-kW powered four-stroke diesel engine using biogas and its heat loss analysis. The biogas is obtained from food waste consisting of methane (CH4)—88.1% and carbon dioxide (CO2)—11.8% as the composition. The biogas (BG) is selected by mass basis ranging from 20% to 60% with 10% increments and is used to operate the engine by dual-fuel mode. The effect of three injection timings such as 25.5 deg (retarded), 27.5 deg (actual), and 29.5 deg (advanced) before top-dead center (bTDC) under dual-mode operation to enhance the properties of the engine is studied, and the results are compared with diesel mode at actual injection timing. Maximum brake thermal efficiency of 30.1% was observed for BG20 operated at 29.5-deg bTDC injection timing (IT). The dual mode operated at the injection timing of 29.5-deg bTDC showed an increase in cylinder pressure compared to diesel by 11.9% at full load conditions, whereas carbon monoxide emission was lower by 5.2% at 29.5-deg bTDC IT than diesel, and nitrogen oxide emission was lower at 25.5 deg bTDC IT than diesel mode by 45%. Besides, at 75% engine load, the least amount of heat losses was observed for BG50 exhibiting effective conversion of fuel energy into equivalent work higher than that of diesel by 2.2%, respectively.

Numerical study of turbulent jet ignition process at different injection strategies in a single-cylinder engine with active pre-chamber

ABSTRACT The application of lean-burn technology in engines that aims to meet the low-carbon combustion promotes the development of turbulent jet ignition (TJI) system. A turbulent jet ignition system has great potential in improving ignition stability and accelerating flame propagation. In this study, a numerical investigation of the turbulent injection ignition process in a single-cylinder engine with an active pre-chamber is conducted. The turbulent jet ignition mechanism and the effects of pre-chamber injection timing, injection quantity, and spark ignition timing on the jet ignition process and combustion characteristics are analyzed comprehensively. Based on the temperature and composition at the nozzle, the jet ignition process in the engine can be divided into three main phases:1) cold jet. 2) flame jet. 3) full combustion. It was found that the fuel vapor in the pre-chamber will decrease due to the less time for fuel evaporation when the injection timing is excessively delayed. Larger injection quantities will increase the inhomogeneities in the pre-chamber, which further play an important role in the ignition efficiency of the TJI system. Delaying the spark ignition timing will significantly influence the thermodynamic condition in the combustion and correspondingly change the overall combustion progress. For pollutants, most of the nitrogen oxide emissions in jet ignition engines mainly come from the pre-chamber, while the soot emission is produced in the cylinder.

Corrigendum to “Effects of gas injection timing on combustion instability for a spark ignition natural gas engine under low load conditions” [Appl. Therm. Eng. 206 (2022) 118144

Corrigendum to “Effects of gas injection timing on combustion instability for a spark ignition natural gas engine under low load conditions” [Appl. Therm. Eng. 206 (2022) 118144

Experimental study on the effects of injection timing and n-butanol energy ratio on combustion and emissions of n-butanol/diesel DFDI engine

In this paper, a dual-fuel direct injection (DFDI) system was designed by utilizing two common-rail direct-injection systems in a modified single-cylinder engine. Diesel and n-butanol were directly injected to realize the stratifications of fuel-air mixtures and reactivity. The effects of the n-butanol energy ratio (BER) and fuel injection timing on engine combustion and emission characteristics were studied under low and medium load. The combustion phase was retarded, indicated thermal efficiency (ITE) decreased and COV of IMEP increased as increasing BER under each load. Under low load, the n-butanol injection timing was suggested near 125° CA BTDC to increase ITE, by modifying the stratification of the n-butanol at a favorable level. With an advance of diesel injection timing, the combustion phase was advanced at first and then retarded; ITE was also increased firstly and then decreased. Under medium load, the two-stage high temperature heat release event could be observed. Early n-butanol injection condition was preferred to achieve higher ITE and lower COV of IMEP. The early diesel injection operation was suggested under medium load for increased ITE, together with the decreased nitrogen oxide and soot emissions. In general, compared with pure diesel operation, stable and high-efficient combustion could be achieved in n-butanol/diesel DFDI mode, while the ITE could increase 2.8%; NOx and Soot emission decreased 82% and 79%.

Experimental Study of Cyclic Variations of RCCI Diesel–Methanol Engines at Multiple Simulated Elevations

Abstract The cyclic variations of reactivity-controlled compression ignition (RCCI) combustion are studied in this work via experiments conducted in an in-house diesel–methanol dual-fuel (DMDF) engine at multiple simulated elevations. The test engine is maintained at 1800 rpm, with simulated elevations of 10, 700, and 1670 m. Engine load, methanol substitution rate (MSR), and injection parameters are varied to investigate their effects on cyclic variations at multiple elevations. We employ in-cylinder pressure parameters, such as the maximum pressure (Pmax) and indicated mean effective pressure (IMEP), to quantify cyclic variations. According to the results, the stability of DMDF combustion in plateau conditions displays a similar trend to that in plain conditions. However, with the increase in elevation, there is a significant increase in the Pmax coefficient of variation (COVPmax), while that of the IMEP (COVIMEP) shows an opposite trend. The distribution of crank angle at high elevations corresponding to Pmax tends to be more concentrated, and the increase in pilot injections reduces the COVPmax in the plateau environment. At all elevations, there is no effect of injection timing on COVIMEP, while COVPmax is more sensitive to injection timing (range from 10 deg CA before top dead center (BTDC) to 3 deg CA BTDC). Compared with other injection parameters, the cyclic variations caused by injection pressure (range from 92 MPa to 112 MPa) are relatively minor.

Experimental Investigation and RSM Modeling of the Effects of Injection Timing on the Performance and NOx Emissions of a Micro-Cogeneration Unit Fueled with Biodiesel Blends

The (partial or total) substitution of petro-diesel with biodiesel in internal combustion engines (ICEs) could represent a crucial path towards the decarbonization of the energy sector. However, critical aspects are related to the controversial issue of the possible increase in Nitrogen Oxides (NOx) emissions. In such a framework, the proposed study aims at investigating the effects of biodiesel share and injection timing on the performance and NOx emissions of a diesel micro combined heat and power (CHP) system. An experimental campaign has been conducted considering the following operating conditions: (i) a reference standard injection timing (17.2° BTDC), an early injection timing (20.8° BTDC), and a late injection timing (12.2° BTDC); (ii) low (0.90 kW), partial (2.45 kW), and full (3.90 kW) output power load; and (iii) four fuel blends with different biodiesel (B) shares (B0, B15, B30, and B100). Experimental data were also elaborated on thanks to the response surface modelling (RSM) technique, aiming at (i) quantifying the influences of the above-listed variables and their trends on the responses, and (ii) obtaining a set of predictive numerical models that represent the basis for model-based design and optimization procedures. The results show: (i) an overall improvement of the engine performance due to the biodiesel presence in the fuel blend —in particular, B30 and B100 blends have shown peak values in both electrical (29%) and thermal efficiency (42%); (ii) the effective benefits of late SOI strategies on NOx emissions, quantified in an overall average NOx reduction of 27% for the early-to-late injection, and of 16% for the standard-to-late injection strategy. Moreover, it has emerged that the NOx-reduction capabilities of the late injection strategy decrease with higher biodiesel substitution rates; through the discussion of high-prediction-capable, parametric, data-driven models, an extensive RSM analysis has shown how the biodiesel share promotes an increase of NOx whenever it overcomes a calculated threshold that is proportional to the engine load (from about 66.5% to 85.7% of the biodiesel share).

Influence of Pilot Injection on Combustion Characteristic of Methanol–Diesel Dual-Fuel Engine

An experimental study regarding methanol–diesel dual-fuel (DF) engines was conducted on a modified engine to explore the effects of pilot injection timing and period on the two-stage combustion process caused by the pilot injection strategy. In this study, the two-stage combustion process was determined according to the first two peaks of the second derivative of an in-cylinder pressure (d2p/dφ2) curve. The results show that the peak pressure rise rate (PRR) tended to decrease with advancing pilot injection timing at a high co-combustion ratio (CCR), which reduced combustion noise. The start of the combustion of the main injection diesel (SOC2) could be advanced by increasing the pilot injection period or advancing pilot injection timing at a 42% CCR. At an 18% CCR, the pilot injection timing and period had no significant effect on SOC2. With the advancement of pilot injection timing, the start of the combustion of pilot injection diesel (SOC1) advanced, and generally, the coefficient of variation of the PRR (COVPRR) of the two-stage combustion process increased first and then decreased. However, with the increase in the pilot injection period, SOC1 almost always remained constant and the COVPRR of the two-stage combustion process generally increased.

Optimization of the application of the CRISPR/Cas9 system in Mythimna separata

AbstractMythimna separata (Walker) (Lepidoptera: Noctuidae) is one of the most destructive phytophagous pests. Here we present detailed instructions to achieve successful application of CRISPR/Cas9‐mediated genome editing on M. separata. We optimized procedures, including egg collection and incubation. We further successfully conducted microinjection on the washed eggs by applying water on the egg surface. We then evaluated the effects of injection timing on both egg viability and genome editing efficiency using NPC1b as the target gene. We observed that Cas9 protein injection had significantly less effect on the viability of the eggs at the earlier stage (<2 h old) than at later stages, although no significant effect was observed on the postembryonic development between different egg ages. All larvae were edited when the eggs were <6 h old, and the editing efficiency decreased when older eggs were used. Moreover, mutants were detected among G1 progenies, which demonstrated that the mutation generated by the Cas9/sgRNAs system on M. separata was heritable. As far as we know, this is the first report of CRISPR/Cas9 for this important pest. The successful application of genome editing on M. separata is essential to understanding its biology and developing novel control methods.

Effect of injection timing on combustion, emission and particle morphology of an old diesel engine fueled with ternary blends at low idling operations

Currently, idling emissions and old vehicle emissions have attracted more and more attention. Many countries have made corresponding policies to limit these emissions. In this study, to investigate the combustion, engine performance, and emission characteristics of an old diesel engine fueled with diesel-palm biodiesel-ethanol (DPE) ternary blended fuels according to various multiple injection strategies under low idling conditions, a series of experiments were carried out on an old common-rail direct injection (CRDI) diesel engine. The engine speed and load were fixed at 750 rpm (the lowest speed) and 30 Nm, respectively. Two test modes of A (only pilot injection timing was variable) and B (only main injection timing was variable) were comparative studied. The experimental results show that the main-pilot injection timings and DPE ternary blends have significant impacts on the engine performance, combustion and characteristics. Overall, as the ethanol concentrations in DPE ternary blends increase, brake specific fuel consumption (BSFC), maximum heat release rate (HRRmax), ignition delay, carbon monoxide (CO) and hydrocarbon (HC) emissions increase, while nitrogen oxides (NOx) and smoke emissions are simultaneously reduced. The high volatility, high latent heat of evaporation and high oxygen content of ethanol may play a major role in reducing NOx and smoke emissions. In addition, the primary particle diameter of all tested fuels is distributed in a narrow range of 18–24 nm, and the addition of ethanol is beneficial to reduce the particle diameter.

Effect of injection timing on the performance of CRDI diesel engine fuelled with fish oil biodiesel and its blends doped with pyrogallol antioxidants

In the present study an experimental work has been conducted to characterize the fish oil biodiesel and their blends with diesel and Pyrogallol antioxidant respectively. Fish oil biodiesel (FHOBD) is blended with diesel to produce FHOBD B20. Further to study the effect of antioxidant addition to FHOBD B20, three blends with varied dosage of pyrogallol are prepared. Accordingly, FHOBD B20 is infused with 1, 2, and 3 grams of pyrogallol antioxidant per liter to produce FHOBD B20PG1, FHOBD B20PG2 and FHOBD B20PG3 respectively. Beyond 3 gm deterioration in the blend homogeneity is observed. For the CRDI engine performance evaluation only FHOBD B20PG3 is considered. Advancing the injection timing to 17o BTDC resulted into improved CRDI engine performance powered with fish oil biodiesel. Further adding Pyrogallol antioxidant into FHOBD B20 blends higher BTE, lower emissions of smoke, HC and CO emissions were obtained for the CRDI engine respectively.

Small bubbles formation and contribution to the overall gas holdup in large diameter columns of very high viscosity oil

A limited number of studies are available in literature on the small bubbles which create from gas-very high viscosity oils interaction and its contribution to the gas holdup in the system. The rate of small bubble formation has an important impact on heat and mass transfer in many chemical and industrial processes. The work presented in the current paper provides unique information on the formation of bubbles of millimetre diameter in high viscosity oil. A column of 290 mm diameter and Silicon oil of 330 Pa.s viscosity, were employed besides Electrical Capacitance Tomography and a high-resolution camera to investigate the characteristics of the small bubbles. Mechanism of bubble generation, effect of gas injection time and flowrate were studied. The average void fraction, total gas-liquid height, overall Probability Density Function (PDF) profile, small bubbles volume fractions and diameter were measured. Small bubbles generate from the eruption of large bubbles, at gas injection nozzles, coalescence of large bubbles, and at liquid bridges at transition to churn flow regime. Properties and concentration of the small bubbles are controlled by the location of the bubble generation, gas flowrate, and gas injection time. Small bubbles contribute by 6.6- 30% to the total gas holdup. Bubble diameter increased from 0.68 mm to 0.75 mm and decreased from 1.1 mm to 0.75 mm at the top and the bottom sections of the column respectively after 60 minof gas injection.

Experimental investigation of water injection and spark timing effects on combustion and emissions of a hybrid hydrogen-gasoline engine

This paper aimed to study the effects of water injection and spark timing on performance of a hybrid hydrogen-gasoline engine. For this aim, a modified four-cylinder turbocharged gasoline direct injection (GDI) engine equipped with hydrogen port injection and port water injection system was developed. In this study, the engine speed was maintained at 1300 rpm and the throttle opening of 30% with an excess air/fuel ratio of 1. The hydrogen energy percentage of 15%, water fuel mass ratio of 0.2 and 0.4 was added into the intake port. When the hydrogen energy percentage was changed, the gasoline fraction was also adjusted to keep the mixture at the stoichiometric. For all tested conditions, the spark timing was varied from 1 to 42°CA before top dead center (BTDC) with a fixed interval of 2°CA. Experimental results showed that maximum brake torque (MBT) spark timing varied when water and/or hydrogen is added. With hydrogen addition, the worsened combustion caused by water injection can be improved. Also, the variation of IMEP and COVIMEP versus spark timing became more insensitive with hydrogen addition. With water injection, the high NO emission caused by hydrogen addition can be largely reduced, however with side effect of higher HC and CO emissions.

Effect of injection timing on combustion, performance and emissions characteristics of methanol fuelled DISI engine: A numerical study

In this paper, the effect of the start of injection (SOI) on the engine characteristics of a methanol-fuelled direct injection spark ignition (DISI) engine is numerically studied. The simulations are performed using CONVERGE CFD software on a wall-guided, four-stroke gasoline direct injection (GDI) engine. The SOI is swept from −120° CA ATDC (crank angle after top dead centre) to −100° CA ATDC at a constant step of 5° CA. The engine speed of 2000 rpm and a compression ratio (CR) of 11:1 is used. It is observed that there exists an optimum injection timing for a given spark timing at which the best compromise is obtained between the performance and emissions. A maximum indicated thermal efficiency (ITE) of 41.66% is obtained in the case of −115° CA ATDC SOI. Emissions like formaldehyde and soot are also found to be the lowest in this case. Engine's ITE is 36% higher for methanol fuel than gasoline when simulated by supplying the same energy input, keeping all the other parameters the same. The total hydrocarbon (THC), carbon monoxide (CO), and soot emissions are 58.2%, 68%, and 73.9% lower for optimised methanol injection timing as compared to gasoline. The NOX emissions are found to be higher for methanol than gasoline due to higher in-cylinder temperature in the case of methanol engine, which is due to higher heat release and proper combustion than gasoline.

Exploring the effects of pilot injection timing and natural gas flow rates on the performance of twin-cylinder compression ignition engine

ABSTRACT Alternative fuels offer various advantages over traditional fossil fuels, including the fact that they are recyclable, sustainable, Contribute to energy independence, and reduce emissions. Renewable fuels such as Compressed natural gas and biodiesel were used in this study. Natural gas is an appealing and appealing fuel because of its vast availability, low Cost, and Clean-burning qualities. The use of biodiesel, namely mustard oil biodiesel, aids in making it Cleaner and more Cost-effective. The present study aims to reduce tailpipe emissions from diesel engines using dual-fuel Combustion, which employs a Combination of fossil and renewable fuels. An experimental analysis was Carried out to evaluate the effectiveness and tailpipe emissions of a twin-cylinder diesel engine fueled by pilot Mustard oil biodiesel (MOB) and CNG, with variations in the rate of CNG flow and time of pilot injection. According to the findings, advanced pilot injection timing (PIT) at 24°CA bTDC (degree Crank angle before top dead Center) and using a lower rate of CNG flow (0.2 kg/h) resulted in the highest brake thermal efficiency (31.21%), while brake specific fuel Consumption decreased by nearly 10% at this setting. Increasing pilot fuel injection to 24°CA bTDC and maintaining a modest rate of CNG flow at 0.2 kg/h in a dual-fuel model decreased NOx emissions by 26% when Compared to diesel alone mode, but resulted in a minor rise in CO emissions. The Current study may aid in the Conversion of a significant number of small to mid-segment diesel engines used in irrigation and the industrial sector in the Indian subcontinent. The study helps in minimizing NOx emissions while also lowering import fossil fuel Costs.

Effects of gas injection timing on combustion instability for a spark ignition natural gas engine under low load conditions

• The entire cycle of in-cylinder pressure time series is applied to study the CCV. • The return maps and phase space reconstruction are used as the analysis methods. • The gas injection timing is used as the impact factor. • The chaotic behavior is stronger when the GIT is near 60°CA ATDC. Experiments are carried out with different GITs under 10% and 25% load conditions to reveal the influence of gas injection timing (GIT) on combustion instability for a spark ignition natural gas engine under low load conditions. The phase space reconstruction and coefficient of cyclic variation (CCV) of the entire cycle in-cylinder pressure time series, the return maps of indicated mean effective pressure (IMEP) and CA50, the distributions of CA5 and CA90 are applied to analyze the combustion instability of the natural gas engine qualitatively and quantitatively. Results show that the combustion process of the natural gas engine presents chaotic characteristics. With increasing GIT from 0°CA to 90°CA ATDC, the CCV and the separation degree of phase space attractor initially increase and then decrease. The distributions of return map points for IMEP and CA50 initially disperse and then concentrate, and the combustion instability and chaotic characteristics are initially enhanced and then weaken. When the GIT is near 60°CA ATDC, the chaotic characteristics of combustion instability for the natural gas engine is the strongest. The reasons for the influence of GIT on combustion instability of the natural gas engine are identified based on 3D computational fluid dynamic (CFD) simulation, showing that the pressure difference between in-cylinder and the intake manifold under different GITs leads to the difference in the mixing degree of the natural gas and air as well as the CH 4 concentration distribution of in-cylinder. This finding provides a theoretical basis for improving the lean-burn stability of natural gas engines.

Effect of split injection strategies on diverse characteristics of a common rail direct injection diesel engine operating with diesel-palm oil-ethanol micro-emulsions

This study investigated the effect of pilot injection timing (PIT) and pilot injection quantity (PIQ) on the performance of a common rail direct injection (CRDI) diesel engine with two-stage injection system operating with diesel-palm oil-ethanol micro-emulsions. The results indicated that, at low engine load, the maximum in-cylinder pressure (Pmax) and peak of heat release rate (HRR) of D35P35E30 were highest, and those of D100 were lowest. At high engine load, the Pmax of D100 was highest, that of D60P30E10 was lowest, and the peaks of HRR were almost identical for all test fuels. The Pmax and peak of HRR were slightly increased with the advance of PIT. Increasing PIQ increased the first peak of HRR and reduced the second one. At low engine load, the coefficient of variation (COV) of Pmax and the indicated mean effective pressure (IMEP) presented a slight decrease for the micro-emulsions, but did for D100 at high engine loads. The brake specific fuel consumption (BSFC) of the micro-emulsions was higher, and the brake thermal efficiency (BTE) was also slightly higher when compared with diesel (D100). With the advance of PIT and the increase of PIQ, BSFC was increased, BTE was decreased, and hydrocarbon (HC) emissions were reduced. The variation of PIT and PIQ had little effect on the particle number concentration (PNC), but had evident effect on nitrogen oxides (NOx) emissions. It was concluded that the micro-emulsions can be used to reduce NOx and particulate matter (PM) simultaneously combined with injection strategy in a diesel engine.

Effects of multiple injections on the combustion and hydrocarbon emission characteristics of the start cylinder in direct-start process

Improving the engine starting strategy is of great significance for enhancing its combustion and emission performances. Compared with conventional start-stop systems, the direct-start process has been widely considered an efficient, viable, and low-cost solution for gasoline direct injection (GDI) engines to guarantee frequent startups. This paper proposes a novel direct-start process by introducing multistage and split injection strategies to improve the fuel–air mixture preparation, in which the effects of injection numbers and split injection timings on combustion, motion, and hydrocarbon (HC) emission characteristics are experimentally investigated. Results show that both multistage and split injection strategies achieve better starting performances than the traditional single injection approach, with the significantly advanced start points of heat release and cylinder pressure, increased peak heat release rate (HRR), enhanced accumulative heat release, shortened CA50, and promoted start combustion efficiency. The faster and more complete combustion leads to a lower bottom point of the piston. Meanwhile, the HC emissions decrease, especially under equivalence ratios of 0.6–0.8. Comparing the two strategies, the direct-start process with a three-stage injection possesses an earlier start point of heat release, while that with a split injection timing of 1 ms holds a shorter CA50 (18.91 ms), higher peak HRR (∼200 J/ms), and higher start combustion efficiency (52.16%). Moreover, under the optimal equivalence ratio range of 0.6–0.8, the engine with the split injection timing of 1 ms has better motion and HC emission characteristics.

Evaluating the effect of variable methanol injection timings in a novel co-axial fuel injection system equipped locomotive engine

Methanol has been identified as a potential substitute for conventional fuels (diesel, petrol) from scalability, sustainability, and an economic viewpoint. Economically, methanol could be cheaper than conventional fuels based on the price per MJ energy. This study evaluated the possibility of displacing the diesel (90% on an energy basis) by methanol in the locomotive engine using a novel co-axial injection concept while evaluating the different methanol injection timings. Pilot diesel injection (10% on an energy basis) ensured the combustion of injected methanol. A 1-D model of a 16-cylinder locomotive engine was developed for the parametric study to identify a suitable methanol injection strategy corresponding to co-axial injector configuration. Three different parameters were selected to investigate the effect of the new co-axial injection system on the engine performance, combustion, and emissions. These were (i) methanol injection timing, (ii) nozzle design parameters (hole diameters and the number of holes) for methanol injection, and (iii) nozzle design for diesel injection. Three different methanol injection strategies (ITM1, ITM2, ITM3) were evaluated at eight different notches of the locomotive engine for identical diesel injection timings of the validated base model. ITM1 emerged as the best strategy to inject methanol into the engine cylinder because of relatively higher in-cylinder pressure and comparable heat release rate (HRR). The maximum in-cylinder pressure (Pmax), the crank angle at maximum pressure (°CA Pmax), the start of combustion (SoC) duration, combustion duration (CD), and torque were comparable to the baseline diesel-only fuelling. For this strategy, co-axial injector design parameters [diesel's nozzle diameters (HDD) = 0.2 mm, number of nozzles for diesel (NHD) = 4, methanol nozzle diameters (HDM) = 0.35, number of nozzles for methanol (NHM) = 9)] exhibited promising results. Overall, the first injection strategy emerged as the best for direct methanol injection in the locomotive engine at all engine loads. The main finding of this study was that since methanol had a higher latent heat of vaporization, it should not be injected too late after the diesel pilot injection. This means that methanol must be injected in a sufficiently hot environment to easily vaporize it to ensure its participation in combustion without struggling for evaporation due to the colder in-cylinder environment. The methanol showed relatively lower environmental impact in all three strategies by significantly reducing the NOx emissions. NOx control is a major challenge for the surface transport industry. It could be resolved using methanol, which may expedite its use in internal combustion engines (ICEs), cleaning up the combustion engine based transportation. This simulation study demonstrated that petroleum usage and its negative environmental impact could be reduced by using cleaner/greener methanol.

Investigation of bifurcations in cyclic combustion dynamics of a CNG-diesel RCCI engine

This study uses nonlinear dynamical and chaotic methods to investigate the cyclic combustion dynamics of a CNG-Diesel reactivity control compression ignition (RCCI) engine. The experiments of RCCI combustion mode are conducted on a single-cylinder automotive diesel engine with the development ECU. Low reactivity fuel (i.e., CNG) is injected into the intake manifold, and high reactivity fuel (i.e., diesel) is injected directly into the engine cylinder during the RCCI experiments. Mass of fuel injection per cycle and their injection events are controlled by using ECU. The engine is tested for fixed engine load and speed of 3 bar BMEP and 1500 rpm, respectively. A double diesel injection strategy is used for injecting the diesel fuel into the engine cylinder. In-cylinder pressure is measured using a piezoelectric pressure transducer on a crank angle basis with a resolution of 0.1 CAD. Combustion parameters are calculated on a cyclic basis from measured in-cylinder pressure. In this study, the effect of diesel injection timing (SOI-2) on the behavior of combustion dynamics for two different masses of port-injected CNG fuel (mc) is investigated. The CA50 time series of 1000 consecutive engine cycles is analyzed for combustion dynamics analysis using symbol sequence analysis, return maps, recurrence plots (RPs), recurrence quantitative analysis (RQA), and 0–1 test. The peaks in symbol sequence histograms and the corresponding symbol series depict the period-2 nature of the cyclic combustion dynamics at the intermediate SOI-2 of 30° and 40° bTDC. Return maps also confirm the onset of noisy period-2 bifurcation at 30° bTDC SOI-2. The dominance of deterministic period-2 characteristics is found in the cyclic combustion dynamics at 30° and 40° bTDC SOI-2 using recurrence plots. The 0–1 test method depicts stronger chaotic cyclic combustion dynamics at 20° and 50° bTDC SOI-2. In summary, the present study supports the existence of a periodic window in between the chaotic combustion for the intermediate values of SOI-2. The dominance of the deterministic characteristics makes this regime of intermediate SOI-2 values suitable for a better cycle resolved control.

Numerical simulation and experimental investigation on pollutant emissions characteristics of PODE/methanol dual-fuel combustion

The current study focuses on the effects of methanol ratio, injection timing and intake temperature on emission performance of a common-rail engine with polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel combustion mode. Then, the numerical model of dual-fuel combustion is established using CFD software CONVERGE coupled with PODE/methanol chemical kinetic mechanism, and the distribution and evolution characteristics of important radicals, methanol and temperature fields inside cylinder are calculated and analyzed. The results show that the NOx and soot emissions of dual-fuel mode decrease by 12.4% and 26.0% compared with pure PODE at 50% load, but CO and HC emissions increase. With the methanol ratio increasing, the NO and N2O emissions decrease, while the methanol, NO2, HCHO, C2H4, CH4 and C2H6 emissions increase, and the peak HO2 mass of dual-fuel increases by 156.2% compared with pure PODE. With the advance of injection timing and the increase of intake temperature, the generation rate of H and OH radicals in dual-fuel combustion raise, the emissions of NO and NO2 increase, while the emissions of methanol, HCHO, C2H4, CH4 and C2H6 decrease. Therefore, compared with traditional diesel engine, more attention should be paid to the unregulated emissions of NO2, methanol and HCHO for PODE/methanol dual-fuel engine.