Dead Center Research Articles

Effects of Methanol Addition on the Combustion Process of the Methanol/Diesel Dual-Fuel Based on an Optical Engine

The combustion process of traditional diesel engines is mainly determined by the injection timing of diesel. There is a trade-off relationship between the soot and NOx (nitrogen oxides) during this combustion process, making it difficult to reduce these two emissions simultaneously. The use of methanol can not only solve the above problem, but also replace some fossil fuels. However, the effects of methanol injection into the intake duct on the flame propagation in diesel/methanol dual-fuel engines is not yet clear, and there is relatively little research on it. The effects of methanol addition on the combustion process of diesel/methanol dual fuel (DMDF) were achieved based on a modified optical engine in this paper. One injector is installed on the intake inlet to inject methanol, and the other injector is installed in the cylinder to inject diesel in two stages before the top dead center of compression. There are three tests conducted separately in this paper. Firstly, the effects of the methanol ratio (40%, 50%, 60%, and 70%) on the combustion process are investigated, with the total heat remaining unchanged. Secondly, the effects of the pre-injection mass of diesel (20%, 30%, 40%, and 50%) on the combustion process are investigated, which keeps the total diesel mass unchanged. Finally, the effects of the total mass of diesel on the combustion process are investigated while maintaining the mass of methanol unchanged. The dual-fuel combustion process is recorded by a high-speed camera. A combustion analyzer and other equipment were used to analyze the combustion. The results showed that CA10 is delayed, the pressure and the heat release rate (HRR) are reduced, and the number of pixels of the KL factor (KL) decreases significantly with the increasing methanol ratio. CA10 and CA50 are advanced, the pressure and HRR decrease, and the KL increases when the mass of pre-injected diesel increases. CA10 and CA50 are advanced, respectively, and CA90 is postponed due to the increase in diesel mass. The pressure and HRR increase, and the KL increases when the total mass of diesel increases.

Numerical investigation of the impact of dual spark plug coordinated ignition strategy on the combustion process in a free piston engine generator

The unique motion profile of Free Piston Engine Generators (FPEG) results in a brief dwell period at the top dead centre (TDC). Effectively achieving swift combustion within the cylinder during this limited interval is an urgent challenge that needs to be solved. In this study, a three-dimensional simulation model of FPEG was established and the model underwent calibration utilizing experiment data. Subsequently investigating the impacts of varying ignition positions, distinct spark plug spacing, and distribution on the combustion of the FPEG when subjected to the dual spark plug ignition configuration. The research results show that with the advancement of the ignition position, the maximum combustion duration of the dual spark plug FPEG was shortened by 34 %. With a reasonable spark plug spacing, the dual spark plug FPEG could shorten the flame propagation distance, which is conducive to the realization of constant volume combustion. When the dual spark plugs were arranged on both sides of the auxiliary intake port, the peak pressure in the cylinder could reach up to 49.5 bar. When the dual spark plugs were arranged in the main intake port and the auxiliary intake port, the indicated thermal efficiency reached 34.7 %.

The relationship between fuel reactivity and exergy features in combustion process

Fuel reactivity is a flexible and feasible method to control combustion, thus reactivity-controlled compression ignition (RCCI) has the potential to achieve lower emissions and higher thermal efficiency. However, the exergy loss during combustion hinders the further exergy-work transform, which limits the thermal efficiency further improvement. The present work focuses on the relationship between fuel reactivity and exergy which contains exergy loss (EL) and thermomechanical exergy (Exthermo due to the temperature and pressure imbalance between system and reference state). By varying the reactivity of primary reference fuels (PRFs) with different initial boundary conditions, it is found that different PRFs could not reduce EL and change Exthermo under same condition but could change the exergy loss rate as well as the EL structure by influencing low-temperature combustion. In terms of boundary conditions, both high temperature and lean mixture could improve Exthermo but with different mechanism: high temperature saving EL into Exthermo, lean mixture recovering incomplete combustion exergy (Exincom) into Exthermo. By contrast, equivalence ratio more easily affects EL and Exthermo. In three-dimensional situation, it is found that decreasing reactivity of PRFs leads more in-cylinder area below equivalence ratio 1.0 which benefits for the Exthermo improvement, but it would cause Exthermo structure mutation which is unfriendly for the smooth output of work near top dead center. The conversion of fuel exergy to final useful work is indirect, and there exist two sub-processes: fuel exergy to thermomechanical exergy then thermomechanical exergy to useful work. The final exergy-work transform efficiency is influenced by both processes. Therefore, using low reactivity fuel as PRF90 in engine is favor of the exergy from fuel transforming into Exthermo by more lean mixture, adopting high reactivity fuel as PRF0 is favor of the Exthermo sequential structure which is benefit for the combustion control and useful work extract near top dead center. Therefore, there is potential to further improve the thermal efficiency by using a dual-fuel combination, with the low reactivity fuel creating a low equivalence ratio region to improve the thermomechanical exergy, and the high reactivity fuel achieving precise phase control during the combustion.

Improvement on Thrust Control for Start-Up and Piston Motion of Free-Piston Linear Generator

Free-piston linear generators (FPLGs) without a crank mechanism are promising to be used in hybrid vehicles due to their unique operation characteristics. However, the FPLG currently still faces challenges in the start-up and piston control. In this paper, the start-up and operation process of FPLG are analyzed deeply and the improved thrust control strategies for the linear electric machine (LEM) are presented accordingly. First, the mechanism that the vibration center shifts under the general constant thrust resonance starting method is revealed, considering the asymmetric potential energy caused by non-linear compression spring effect in the combustion chamber. Then, a compensation thrust iteratively adjusted by the vibration offset is added to stabilize the swing center during start-up. Next, the coupling effect between the dead centers under single-stroke independent thrust control method is analyzed, by modeling the piston motion from the aspect of energy flow. Accordingly, an improved thrust control method for coupling suppression is presented to enhance the accuracy and robustness of piston motion. Finally, the performance of the proposed method is verified by controlling a permanent- magnet linear synchronous machine (PMLSM) in experiments and simulations.

Experimental and simulation study on evaporation characteristics of E85 impinging spray under DISI cold-start condition

The direct injection of ethanol-gasoline blended fuel into the engine cylinder near the top dead center (TDC) is evitable to suffer from the wall impingement due to more injection mass required to maintain the same air/fuel ratio with traditional fossil fuels. In this study, the evaporation characteristics of E85 cold-start impinging spray were investigated by experiments and numerical simulation. A constant volume vessel was used to produce the direct-injection spark-ignition (DISI) engine-like conditions. The ultraviolet (UV) – visible (Vis) dual-wavelength laser absorption scattering (LAS) technique was employed to quantitatively measure the individual components evaporation in E85, with the emphasis on the effects of impinging distance, wall temperature and injection pressure on the mixture formation. The results show that although the larger impinging distance rarely influences the evaporation before impingement, it facilitates the E85 evaporation process after impingement due to the better atomization by low boiling point (LBP) components (e.g. ethanol). The effects of cold-start wall temperature on the E85 impinging spray are greatly dependent on the impinging distance. Under the small impinging distance, the ethanol and low boiling point (LBP) components of gasoline evaporate faster after impingement at higher wall temperature, but such effect becomes absent under long impinging distance. Therefore, the smaller impinging distance shows a higher sensitivity to wall temperature. Lower wall temperature leads to a high wall heat transfer, thus potentially extend the evaporation time at the near wall region along the spray axis. At either impingement timing or initial impingement, the LBP component with high latent heat evaporates fast, leading to a decrease of surrounding gas temperature. Increasing injection pressure helps to greatly improve the evaporation of the high boiling point (HBP) component in gasoline under cold-start impingement. The evaporation ratio of E85 increases up to about 18% ∼ 30% than that of E100 at the initial impinging period under cold-start condition.

Experimental analysis of the effect of hydrogen as the main fuel on the performance and emissions of a modified compression ignition engine with water injection and compression ratio reduction

This study aimed to investigate the combined effects of compression ratio (CR), start of injection angle (SOI) and water injection (WI) on the performance, including NOx emissions, of a modified turbocharged compression ignition engine using H2 as the primary fuel and diesel solely as a pilot ignition source. WI and H2 were both injected into the intake manifold just after the charge heat exchanger. Test conditions varied the engine speed from 1500 rpm to 2750 rpm, covering a wide range of the original engine's operating conditions, water mass flow varied from 0 to 0.795 g/cycle and SOI for pilot ignition was studied in the range 10°, 5°, 0° before top dead center. Subsequently, the study examined the combined effect of reducing the engine's CR from 17.5:1 (base) to 13.5:1, in one-point increments, reducing SOI and water addition to further enhance the hydrogen energy share (HES).HES varied from 0 % to 85 % under different engine conditions, and WI and SOI were employed to prevent knocking and ensure that the maximum combustion pressure did not exceed 160 bar. The test results indicate that NOx emissions increase with HES, but reducing the CR results in a reduction in NOx emissions of approximately 50 %. Additionally, WI further reduces NOx emissions by up to 50 %. The experimental evidence demonstrates that combining WI with CR and SOI reduction can effectively lower NOx emissions, achieving an efficiency greater than 35 % and therefore approaching the base diesel mode's efficiency. This also reduces the maximum in-cylinder pressure, allowing for an increase in turbocharger pressure and consequently enhancing the engine's specific power. The maximum engine power achieved was 31.6 kW at 2500 rpm (mean effective pressure of 10.1 bar), with a CR of 15.5, SOI at 10°, 1.5 kg/kWh of water, a HES of 81 %, and a minimum NOx level of approximately 480 ppm, with a maximum combustion pressure below 120 bar.

Influence of Artificially Altered Engine Oil on Tribofilm Formation and Wear Behaviour of Grey Cast Cylinder Liners

This work investigates the influence of altered engine oil on the tribological performance, focusing in particular on wear and interconnected tribofilm formation. For this purpose, Zinc dialkyldithiophosphate (ZDDP) additivated engine oils of different degradation levels, produced in an artificial oil alteration process, were used in tribometer tests with a nitride steel piston ring against a grey cast iron cylinder liner model contact. Parameters were chosen to simulate the boundary and mixed lubrication regime typical for the top dead centre conditions of an internal combustion engine of a passenger car. Wear of the cylinder liner specimens was continuously monitored during the tribometer tests by the radio-isotope concentration (RIC) method, and tribofilms were posteriorly investigated by X-ray photoelectron spectroscopy (XPS). The results clearly show that the steady-state wear rates for experiments with altered lubricants were significantly lower than for the experiments with fresh lubricants. XPS analysis on the formed tribofilms revealed a decrease in sulphide and an increase in sulphate states for altered oils evaluated at 120 °C oil temperature, correlating with a decrease in steady-state wear rate. This finding emphasizes the role of sulphate species in the tribofilm formation process and its anti-wear capabilities, in contrast to the sulphide species and the (poly-)phosphate species, as outlined in most of the ZDDP literature. Moreover, the RIC signal that represents the amount of wear in the engine oil showed a decrease over time for specific altered lubricants and test conditions. These “negative” trends in the wear signal are remarkable and have been identified as an incorporation of wear particles from the lubricant into the tribofilm. This finding is supported by XPS results that detected an iron-oxide layer with a remarkably similar quantity within the tribofilm on the surface. Based on these findings, an assessment of the minimum film formation rate and particle incorporation rate was achieved, which is an important basis for adequate tribofilm formation and wear models.

Experimental study on the effects of injection timing using reuse of waste energy as a fuel on a diesel engine

<p><span>In the course of this study, an eco-friendly alternative fuel was manufactured by transesterifying waste oils with the help of alcohol and a catalyst. As required by the American society for testing and materials (ASTM) requirements, we conducted an analysis on the acquired waste cooking oil biofuel (WOB) to determine its most important properties. We were successful in producing three separate fuel mixes, which we will refer to as BF100WOB0 (100% diesel), BF80WOB20 (80% diesel and 20% biofuel), and BF0WOB100 (100% biofuel) respectively. This research used a diesel engine with direct injection; the engine had a single cylinder, and the computer that operated it was located in the cabin. The results showed that the BF80WOB20 had a 3.8% increase in fuel consumption and a 1.4% loss in thermal efficiency while it was at a temperature of 26.5° b top dead center (TDC) conditions with low injection time led to decreased levels of both nitrogen oxides (NOx) and hartridge smoke level (HSL) emissions. The addition of 20% WOB to the fundamental fuel improved the engine combustion characteristics at 26.5° b TDC. This improvement occurred at the same time.</span></p>

Effects of diesel‐ethanol-waste oil cooking and plastics blends reused in common rail direct injection diesel engine

The purpose of this study was to investigate the feasibility of transesterifying waste oils using alcohol and a catalyst to provide a sustainable fuel alternative. To ensure that the resulting biodiesel met American Society for Testing and Materials (ASTM) criteria, we studied its most important parameters of diesel‐ ethanol-waste oil cooking and plastics blends. We were able to separate out three unique fuel mixtures: BF0 (100% diesel), E20 (20% ethanol and 80% diesel), W20 (20% waste cooking oil and 80% diesel), and P20 (20% waste plastics oil and 80% diesel). In this experiment, a single-cylinder, computer-controlled diesel engine with direct injection was used. Fuel consumption increased by 4.3% for W20, 6.7% for E20, and 0.4% for P20, while thermal efficiency decreased by 2.1% for W20, 4.2% for P20, and 2.1% for E20, based on measurements conducted at 23.5° b Top Dead Center (TDC), Compression Ratio (CR19) under full load. At 23.5° b TDC injection time, NOx emissions were observed to be lower. Adding 20% W to conventional fuel at 23.5° b TDC enhanced the engines combustion characteristics.

Impact of engine control variables on low load combustion efficiency and exhaust emissions of a methane-diesel dual fuel engine

A conventional diesel engine when operated in the reactivity-controlled compression ignition (RCCI) combustion strategy faces challenges of high total hydrocarbon (THC) and carbon monoxide (CO) emissions leading to poor combustion efficiency at low engine loads. The oxides of nitrogen (NOx) versus smoke trade-off, encountered in conventional diesel combustion, is replaced by the NOx-THC trade-off in the RCCI operation. This work focuses on addressing the NOx-THC trade-off issue by systematically investigating the effects of engine control variables, such as, fuel injection timing, exhaust gas recirculation (EGR) and intake throttling, on a light duty compression ignition engine running in a methane-diesel dual fuel mode. The engine is operated at a load of 3 bar gross indicated mean effective pressure and at a speed of 1500 rev/min. Based on relationships identified between engine control variables, combustion parameters, emissions and engine performance, a bottom-up approach is used to combine the control variables synergistically to improve the NOx-THC trade-off. A combination of advanced start of injection timing of diesel (−35 degree crank angle (°CA) after top dead centre), 50% premix ratio and 55% EGR levels along with the end of port fuel injection of methane in the middle of the intake stroke (−270°CA), has resulted in a ∼34 percentage points (from 56% to 90%) improvement in combustion efficiency and a ∼9.5 percentage points improvement in thermal efficiency compared to the baseline low load dual fuel operation while maintaining good combustion stability. THC emission is reduced from 105 to ∼25 g/kWh whilst maintaining low levels of NOx (<0.3 g/kWh).

Comprehensive Analysis of Compression Ratio, Exhaust Gas Recirculation, and Pilot Fuel Injection in a Diesel Engine Fuelled with Tamarind Biodiesel

The global automotive industry is facing significant challenges, including dwindling fossil fuel reserves, rising crude oil prices, and increasingly strict emission regulations. To address these concerns, this study investigates the impact of the compression ratio (CR) and exhaust gas recirculation (EGR) on the performance and emissions of a common rail direct injection (CRDI) diesel engine fuelled with a 20% blend of tamarind seed methyl ester (TSME 20) biodiesel. The study employed an open-type electronic control unit to implement pilot fuel injection at a rate of 30%, 23° before the top dead centre (TDC), and at a higher pressure of 600 bar. Three CRs (16:1, 18:1, 20:1) and two types of EGR (hot and cold EGR at 10%) were evaluated. Diesel fuel at CR 18 was used as a baseline for comparison. The experimental procedure involved conducting tests with TSME 20 at CR 16, 18, and 20. Subsequently, TSME 20 at CR 20 + Hot EGR 10% and TSME 20 at CR 20 + Cold EGR 10% were examined. The results showed that TSME 20 operated at a higher CR (CR 20) exhibited improved diesel engine performance and significant reductions in harmful exhaust emissions. Additionally, cold EGR at 10% was more effective in reducing CO, CO2, and NOx emissions from TSME 20 than hot EGR. The findings of this study provide valuable insights into optimizing diesel engine operation to achieve a balance between performance enhancement and emission reduction through tamarind seed biodiesel blends and different EGR techniques. The implementation of these strategies holds considerable potential in addressing the automotive industry’s challenges, including ecological considerations and fuel price fluctuations.

Experimental study on effects of pilot injection mass strategy on combustion, Performance and emission characteristics of CRDI Engine

This experimental work reports how different pilot masses of biodiesel-blended fuel in Common Rail Direct Injection (CRDI) engines affect engine performance, combustion, and emissions. This experiment used 20MEWCO (20 % Methyl Esters of Waste Cooking Oil + 80 % Diesel) as the test fuel. Several parameters, such as timing and injection mass, affect how the CRDI system delivers fuel. In this work, the pilot injection mass was varied by 5 %, 7.5 %, and 10 %, keeping other factors such as injection pressure at 500 bar and the timing of the pilot and main injections at 36°Crank Angle before Top Dead Centre (bTDC) and 15°Crank Angle before Top Dead Centre (bTDC), respectively. This work reveals that when pilot mass is increased in steps of 2.5%, the combustion performance parameters like cylinder pressure, heat release rate and specific fuel consumption values decrease. Also, it gave off less smoke, carbon monoxide and hydrocarbons than regular diesel with more nitrous oxide. Also, it was found that at 10 % of the pilot mass, carbon monoxide, hydrocarbon, and smoke emissions were significantly reduced, with a slight rise in oxide of nitrogen emissions at the same time, without affecting the engine performance.

Enacted Offstage Images, Reported Onstage Action, and Parallel Fictional Worlds in Dead Centre’s Chekhov’s First Play (2015) and Tim Crouch and Rachana Jadhav’s Total Immediate Collective Imminent Terrestrial Salvation (2019)

This essay addresses how the collision of image, text, and speech in contemporary scripted performances discloses something significant about both being in and thinking about the theatre. It examines cases wherein recent examples of theatre practice disrupt long-standing expectations about the form and function of reported offstage action. While Tim Crouch and Rachana Jadhav’s Total Immediate Collective Imminent Terrestrial Salvation (2019) literalises the relationship between text and performance by putting the play script in the hands of the audience and employing illustrations as a means of reporting that inverts established ekphrastic modes, Dead Centre’s Chekhov’s First Play (2015) literalises offstage presence through the audio narration of a figure named as ‘The Director’. These acts of staging literally key conceptual and practical challenges of theatrical representation work in both cases to reveal instances of mimetic disjuncture. Audiences are not sure which version of each performance to invest in: the staged action or illustrated text of Terrestrial Salvation and the onstage adaptation or The Director’s critical reporting in Chekhov’s First Play. By making available different versions of the same theatrical event, each production connects resonantly to a cultural moment wherein we are often exposed to alternative narratives but may not always recognise or acknowledge these alternate perspectives. Reviewed together, these two productions present a wide-ranging sensorial problematising of theatrical representation. They construct points of meaningful divergence through unscripted performances and the disaggregation of actor and character. Methodologically, this essay works to address these questions of representational multiplicity through a form of discursive practice that reports between the two case study examples. This approach serves to reveal the discourse of theatre and performance studies as frequently grounded in ekphrastic reportings that recount theatrical images no longer available to view. The argument marks out first how reported action and other forms of ekphrastic representation have historically been about what cannot be staged in order to propose that what comes to be unrepresentable in these examples – even as it is the means of representation – is theatrical performance itself. The essay then traces how these metatheatrical questions related to the representational affordance of these performances – in this case to do with impossibility of representing the theatre itself – ripple into wider consequences that can have substantial implications related to race, freedom, and collective endeavour.

Effect of direct methanol injection based on low-flow injector on knock of gasoline engine under heavy load condition

Under appropriate strategies, direct methanol injection can suppress the knock effectively. In this paper, methanol was injected as an anti-knock agent by modified low-flow direct injectors into the cylinder of a high-load port injection gasoline engine. The effects of methanol injection timing and methanol ratio on knock suppression were investigated. The knock intensity (KI), knock probability, and auto-ignition timing were used as the primary basis for quantifying the knock. The results show that methanol injection timing has a significant impact on combustion. Maximum knock suppression can be achieved when methanol is injected near the bottom dead center. The too-early and too-late injections will affect the knock suppression. There was an apparent knock phenomenon when methanol was injected near the end of the compression stroke. When the ratio of methanol is meager, methanol will instead increase the intensity of the knock. As the methanol ratio rises, the knock is gradually and effectively suppressed. There is a specific methanol ratio beyond which higher methanol ratios do not significantly increase the knock suppression effect. When methanol was injected late in the compression stroke, low methanol ratios did not seriously increase the knock intensity, but high methanol ratios did not eliminate the knock either.

Analysis of influences of injection parameters on combustion process based on 2-stroke rod-less opposed piston diesel engine

Global concerns about environmental pollution and fuel consumption are increasing, and as emissions regulations become more stringent, exploring new power and structural forms to optimise diesel engines is the way forward for future breakthroughs in diesel engines. The 2-Stroke Rod-less Opposed Piston (2S-ROPE) has been extensively studied for its vibration-free and simple construction. Compared to conventional four-stroke engines, it has a smaller bore, shorter cycle time, higher power and lower fuel consumption in the same time, making it an ideal power source for small engines. In this paper, the rod-less structure is applied to a two-stroke opposed-piston diesel engine for the first time. Based on experimental verification by spraying, a dynamic high-precision three-dimensional model of computational fluid dynamics (CFD) is established, using lateral injection, to clarify the various airflow patterns that occur in the cylinder during the intake and exhaust of the 2S-ROPE, and investigates the effects of injection timing and injection pressure on the oil–gas mixing and combustion processes in the 2S-ROPE cylinder. The results show that the in-cylinder turbulent kinetic energy is highest at an injection timing of 15° BTDC (Before Top Dead Center) and that fuel injection has the greatest effect on in-cylinder airflow disturbance at this time. At 17.5° BTDC, the duration of in-cylinder combustion was the longest. The effect of injection timing on the burst pressure is linear, for every 2.5° advance, the maximum pressure in the cylinder increases by about 2 MPa. 20 MPa of injection pressure increases, the stall period is shortened by less than 1°, the combustion duration CA10-90 is shortened with the increase in injection pressure, and for every 20 MPa increase in injection pressure, the burst pressure increases by 1 MPa, which is a significant increase.

Machine Learning Prediction and Optimization of Performance and Emissions Characteristics of IC Engine

In this work, a study was conducted to investigate the effects of different biodiesel blends with hydrogen peroxide additive on the performance and emissions of an internal combustion engine under various operating parameters. A CI engine was operated with diesel, four dissimilar biodiesels, and H2O2 at various proportions. The biodiesel blends used were Jatropha (D60JB30A10, D60JB34A6, D60JB38A2, D60JB40), Honge (D60HB30A10, D60HB34A6, D60HB38A2, D60HB40), Simarouba (D60SB30A10, D60SB34A6, D60SB38A2, D60SB40), and Neem (D60NB30A10, D60NB34A6, D60NB38A2, D60NB40). The engine was tested at different injection operating pressures (200, 205, and 210 bar), a speed of 1500 rpm, and a CR of 17.5:1. From the experiments conducted, it was highlighted that, under specific conditions, i.e., with an injection pressure of 205 bar, 80% load, a compression ratio of 17.5, an injection timing set at 230 before top dead center, and an engine speed of 1500 rpm, the biodiesel blends D60JB30A10, D60HB30A10, D60SB30A10, and D60NB30A10 achieved the highest brake thermal efficiencies of 24%, 23.9675%, 23.935%, and 23.9025%, respectively. Notably, the blend D60JB30A10 stood out with the highest brake thermal efficiency of 24% among these tested blends. Similarly, when evaluating emissions under the same operational conditions, the D60JB30A10 blend exhibited the lowest emissions levels: CO (0.16% Vol), CO2 (7.8% Vol), HC (59 PPM), and Smoke (60 HSU), while NOx (720 PPM) emissions showed a relative increase with higher concentrations of the hydrogen-based additive. The D60HB30A10, D60SB30A10, and D60NB30A10 blends showed higher emissions in comparison. Additionally, the study suggests that machine learning techniques can be employed to predict engine performance and emission characteristics, thereby cutting down on time and costs associated with traditional engine trials. Specifically, machine learning methods, like XG Boost, random forest regressor, decision tree regressor, and linear regression, were utilized for prediction purposes. Among these techniques, the XG Boost model demonstrated highly accurate predictions, followed by the random forest regressor, decision tree regressor, and linear regression models. The accuracy of the predictions for XG Boost model was assessed through evaluation metrics such as R2-Score (0.999), Root Mean Squared Error (0.540), Mean Squared Error (0.248), and Mean Absolute Error (0.292), which allowed for a thorough analysis of the algorithm’s performance compared to actual values.

Study on the Effect of Secondary Injection on the Combustion and Emission of n-Butanol Engines.

n-Butanol, as a biological alternative fuel containing oxygen, has similar physical and chemical properties to gasoline and has a wide range of sources, which has attracted more and more attention and research. Direct injection technology has been widely used in the field of internal combustion engine due to its advantages of flexibility and control ability. In this paper, the secondary injection of n-butanol engine under the mode of in-cylinder direct injection is discussed to organize stratified combustion of the mixture, optimize combustion to improve the thermal efficiency, and reduce emission. A four-cylinder four-stroke spark ignition (SI) engine was selected to carry out the secondary injection experiment of n-butanol under the excess air ratio (λ) of 1, an engine speed of 1500 r/min, and a low load, and the variables were the second injection ratio and timing. The results show that the secondary injection of n-butanol can achieve stratified combustion of the mixture, but only at a specific second injection timing such as 100°CA before compression top dead center (BTDC) or 125°CA BTDC, the combustion effect is the best. A small second injection ratio can optimize combustion, improve brake thermal efficiency, and reduce hydrocarbon and carbon monoxide emissions. When the second injection ratio is greater than 60%, it results in incomplete fuel combustion, a 3 to 4% reduction in thermal efficiency, and an increase in emissions. Coefficient of variation (COV) was increased by secondary injection, but the effect was insignificant in the small injection ratio, and it will increase with the increase of the second injection ratio. The change of particle number is mainly affected by the nuclear particle number, and with the increase of the second injection ratio, the total particulate number is more affected by the second injection timing. The second injection ratio of 40% can reduce the total particle number under the mixed-gas stratification condition.

ENHANCED DIAGNOSTIC TECHNIQUES FOR MARINE DIESEL ENGINES: ACHIEVING IMO DECARBONIZATION COMPLIANCE

This paper discusses hardware-based methods for monitoring the operational parameters of marine diesel engines and online mathematical modeling techniques (digital twins) for calculating the emissions of CO2, NOx, soot, and other harmful pollutants. It is demonstrated that measuring and analyzing the engine's vibrational diagrams in parallel with gas pressure diagrams in the cylinders allows the evaluation of the actual fuel injection and gas distribution timings. The obtained data is used to refine the mathematical model of the engine's working process, which determines the engine's indicator parameters and power, as well as the emission of harmful substances that need to be monitored in compliance with current IMO requirements. The authors have accumulated experience in using the discussed hardware-based methods for diagnosing marine engines during operation. The hardware and software methods discussed have been implemented into a real-time system for in-service diagnostics of marine engines. The system is designed based on a modern dual-core controller with high performance and low power consumption, incorporating a high-speed ADC with sufficient capability to monitor the working process with a 0.1-degree crankshaft rotation resolution for all types of marine main and auxiliary engines. The system also utilizes wireless data transmission technology. A contemporary Android/iOS smartphone or tablet serves as the computational and graphical component of the system. This real-time system enables the utilization of all the advantages of parallel pressure and vibroacoustic analysis, including real-time determination of key operating parameters, identification of top dead center position, and evaluation of fuel delivery and gas distribution phases. Additionally, it harnesses the benefits of employing a digital twin—an online mathematical model of the engine cylinder's working process. These solutions will enhance diagnostic quality and, ultimately, improve the operational efficiency of marine engines by reducing operational costs and extending the period of reliable, trouble-free operation.

Fuel reactivity stratification assisted jet ignition for low-speed two-stroke ammonia marine engine

Ammonia (NH3) has gained much attention as a carbon-free fuel due to its great potential to reduce carbon emissions in the shipping industry. However, ammonia is difficult to use directly in existing marine engines due to its low flame propagation speed and high auto-ignition temperature. In this work, a new combustion mode for low-pressure injection low-speed two-stroke ammonia marine engines: Reactivity Stratification Assisted Jet Ignition (RSAJI) is proposed and explored. The results of the study show that the RSAJI mode is very promising. Especially at low and medium loads, the peak pressure can be increased by 27.3%, and NH3 and N2O emissions in the exhaust gas can be reduced by 87.1% and 99.7%. Two key parameters: direct injection timing and ammonia substitution rate (ASR) determine the reactivity stratification in the main-chamber, which directly affects the jet ignition effect and turbulent flame speed. A thorough analysis of engine performance shows that the injection timing should be appropriately far from the Top Dead Center (75°CA BTDC & 86.4°CA BTDC). Further increases in ammonia substitution rates (ASR = 90%, 95%) will result in a reduction in power performance gains but will improve the indicated thermal efficiency (>50%).

Experimental observation of the TJI-initiated HPDI gas combustion: Vertically crossed flame jet and methane jet

In the field of natural gas marine engines, the high-pressure direct injection (HPDI) technology is widely used to achieve emission reduction while maintaining equivalent thermal efficiency and power output compared to diesel engines. In these engines, the in-cylinder combustion is primarily initiated by the diesel spray flame near the top dead center (TDC). In the present work, pre-chamber turbulent jet ignition (TJI) is employed to substitute diesel injection to initiate the combustion of HPDI methane jets. The optical experiments of ignition and flame development in the TJI-HPDI system with various injector configurations and injection/ignition control parameters are conducted in a constant-volume combustion chamber (CVCC). It is revealed that with the increase of injection-ignition delay(ti), three ignition modes are observed sequentially: methane jet suppresses ignition, methane jet first suppresses ignition then promotes flame propagation, and direct ignition and promoted flame propagation. The effect of various injection-ignition delays and injection pulse width were explored. The injection-ignition delay significantly influences the combustion characteristics such as heat release rate, while the injection pulse width influences the duration of the lifted jet flame. The flame lift-off length first decreases and then increases due to variations in thermodynamic conditions and oxygen concentration. With a larger-nozzle injector, the critical injection-ignition delay to initiate the main chamber combustion is significantly reduced. Moreover, the use of different nozzle diameters leads to varying levels of turbulent intensity in the methane jet, which in turn affects the combustion behavior.