Injection Diesel Research Articles

Multi-objective optimization of the performance for a marine methanol-diesel dual-fuel engine

Marine methanol-diesel compound combustion (DMCC) engines have received extensive attention in the shipping industry. This work aims to further improve the performance and evaluate the carbon reduction potential of the marine DMCC engine. First, the computational fluid dynamic model of the dual-fuel engine was built. Then, an intelligent regression method based on the grey wolf optimizer (GWO) algorithm optimized support vector machine regression (SVR) was proposed. The methanol substitution rate (MSR), excess air ratio (EAR), and diesel injection timing (DIT) were adopted as the decision variables to establish the regression models for NOx, CO, and CO2 emissions and indicated specific fuel consumption (ISFC). Subsequently, a multi-objective grey wolf optimizer (MOGWO) and entropy weight TOPSIS were employed to obtain the optimal case for achieving low NOx and CO emissions and ISFC. Finally, the maximum MSR was explored to achieve greater carbon reduction benefits while balancing the NOx emission and ISFC. The results showed that after GWO optimization, the coefficients of determination of the SVR regression models are all greater than 0.95, with mean square errors consistently below 0.015. It indicates that the regression models have excellent consistency and applicability. The optimal case calculated by MOGWO and entropy-weighted TOPSIS enables co-optimization of the NOx emission and ISFC while maintaining the CO emission below 600 ppm. Compared to the original case, the optimal case achieves reductions of 26.22 % for NOx and 13.39 % for ISFC. The exploration of the maximum MSR reveals that in the Pareto optimal set, the maximum MSR reaches 56.16 %, at which point the NOx and CO2 emissions reduce by 75.85 % and 59.32 % respectively, while the ISFC increases by 21.67 % compared to the original case.

Experimental Study on the Diesel Injection Pressure of Homogeneous Charge Induced Ignition for Multi-cylinder Operation

Experimental Study on the Diesel Injection Pressure of Homogeneous Charge Induced Ignition for Multi-cylinder Operation

Experimental investigation and gray relational optimization of engine parameters to improve the output characteristics of an ammonia biodiesel powered dual fuel combustion engine

An innovative approach to this research is to evaluate the effects of different concentrations of biodiesel with premixed ammonia energy in a dual-fuel combustion engine and determine the best operating conditions for optimal engine responses. Experimental results of a 40% ammonia energy premixing fraction with direct injection of a biodiesel blend of 30% (40%AEPF + B30) at 80% load improved brake thermal efficiency (BTE) by 8.42% while reducing brake specific energy consumption (BSEC) by 13.28%. It also reduces the hydrocarbon (HC) emission by 16.8%, the carbon monoxide (CO) emission by 15.06%, and the smoke opacity by 26.8%. As opposed to this, carbon dioxide (CO2) and nitrogen oxide (NOx) emissions are elevated by 21.5% and 16.54%, respectively, relative to the 40% ammonia energy premixing fraction with direct injection of diesel (40%AEPF + Diesel). Thereafter, the ANOVA technique is also utilized to analyze the impact of operational parameters, and the findings show that the responses are statistically significant. Additionally, the results are utilized in a grey relational analysis (GRA) based optimization process to determine the appropriate operational variables. According to optimization results, 40%AEPF + B30 at 80% load provides the most efficiency and fuel economy. It is capable of being used as an alternate fuel instead of conventional diesel.

Study of the effect of cavitation flow patterns in diesel injector nozzles on near-field spray atomization characteristics using a LES-VOF method

The spray atomization process plays a critical role in achieving high efficiency and reducing emissions in internal combustion engines. The fuel injection atomization process, especially the spray primary atomization process, is significantly influenced by turbulent flow and cavitation phenomena within the nozzle. In this study, based on the coupled large eddy simulation(LES) and a volume-of-fluid (VOF)method, the effects of four typical nozzle internal flow patterns on the spray primary breakup in the near-nozzle region were investigated. To realize this objective, the generation of four distinct flow patterns was accomplished through the design and construction of corresponding nozzle structures: (1) nearly single-phase flow in a tapered-orifice nozzle with low orifice location, (2) strong geometry-induced sheet cavitation flow with sheet region extending to the nozzle orifice exit in a normal cylindrical orifice, (3) vortex-induced string cavitation flow in a tapered-orifice nozzle with relative high orifice location, and (4) geometry-induced sheet cavitation is partially suppressed while it is enhanced in the orifice region close to exit in a convergent-divergent orifice. The numerical results unequivocally reveal that the initial atomization of the spray exhibits remarkable efficacy in the case of the conventional cylindrical nozzle, characterized by internal regions of substantial sheet cavitation, despite a relatively minimal flow discharge coefficient. Conversely, the normal tapered-orifice nozzle, lacking significant cavitation, demonstrates a larger flow discharge coefficient, yet its initial atomization performance is notably suboptimal.It is worth noting that the appropriate vortex-induced cavitation in the nozzle can correspond a higher flow rate with a thin string-type cavitation and simultaneously a better spray atomization quality with a strong vortex flow. Also it is concluded that a convergent-divergent nozzle with appropriate transition location can achieve strong atomization .

Experimental Research on the Carbon Dioxides Reduction Potential by Substitution Gasoline with Ethanol and Propane Under Reactivity Controlled Compression Ignition in a Single Cylinder Engine

In this experiment, it was experimentally investigated the combustion and exhaust characteristics, as well as the thermal efficiency, of RCCI combustion using gasoline, ethanol, and propane as low-reactivity fuels under four operating conditions. For each operating condition, gISNOx was limited to 0.15 g/kWh, and gISSmoke was limited to below 15 mg/kWh. The experiment was conducted by determining the operating conditions that satisfied these limitations and resulted in the highest city thermal efficiency. The low-reactivity fuels were supplied by port injection, while diesel was directly injected into the combustion chamber using a diesel injector. As a result, when gasoline is replaced with low-carbon fuels like ethanol and propane, the reduction in CO2 emissions occurred. Under maximum power conditions, using ethanol allowed for a maximum reduction in CO2 emissions of 6.81%. Depending on the driving conditions, ethanol showed a reduction ranging from 3.60 to 6.81%, while propane exhibited a reduction ranging from 3.10 to 5.64%. Additionally, by substituting with ethanol and propane, the GIE could be improved up to 44.73 and 43.56%, respectively.

Optimization of methanol/diesel dual-fuel engines at low load condition for heavy-duty vehicles to operated at high substitution ratio by using single-hole injector for direct injection of methanol

Methanol, as a low-carbon and easily synthesizable fuel, is one of the promising directions for future internal combustion engine (ICE) fuels. However, methanol/diesel engines with high energy substitution ratios exhibit a significant drawback at low loads, namely poor fuel economy, which seriously hinders the development of dual fuel engines. Therefore, this paper conducts an optimization study on the combustion strategy of methanol/diesel in heavy-duty vehicle engines under high energy substitution ratios (70 %) and low loads. Innovatively combines single-hole injection with the direct dual fuel stratification (DDFS) technology. By coupling the longer injection duration of a single hole with higher injection pressure, and tailored combustion strategy adjustments, successfully achieving the goal of optimizing low-load methanol dual fuel engines. The research results indicate that when employing a methanol single-stage injection strategy, setting the start of diesel injection (SODI) of −25°CA after top dead center (ATDC) effectively enhances the combustion efficiency of methanol/diesel, especially when combined with a strategy that the start methanol injection (SOMI) is of −23°CA ATDC. This combination can boost the gross indicated thermal efficiency (ITEg) to 51.95 %. The research on utilizing a methanol two-stage injection strategy found that increasing the methanol premixing appropriately, within the engine's safe range, can effectively enhance ITEg. Specifically, with the methanol pre-injection ratio (MPR) of 10 % and the methanol two-stage injection interval (MII) of 20°CA, ITEg can be improved to 52.07 %. However, excessively of premixing can lead to premature combustion, causing an increase in negative work during the compression stroke and consequently reducing ITEg. This study has unveiled effective solutions for the application of methanol/diesel DDFS technology in the automotive engine field. It offers insights into the selection and optimization of methanol injectors and provides theoretical support and practical references for achieving clean and efficient combustion in engines.

Flame characteristics and abnormal combustion of ammonia-diesel dual-fuel engine with considering ammonia energy fractions

Carbon neutrality is a significant challenge but also an essential opportunity for internal combustion engines (ICE), and fueled with low-carbon fuels is the key for ICE to reduce carbon emissions. Ammonia is a carbon-free fuel, whereas ammonia-diesel dual-fuel (ADDF) combustion can provide efficient and clean combustion of ammonia. In this study, the flame characteristics and abnormal combustion of ADDF engines are studied by considering ammonia energy fractions and diesel injection timings. The results show that a high ammonia energy fraction led to an extended period of combustion, while the CA05 first advances and then decreases with the decrease of ammonia energy fraction. This phenomenon indicates that an easily ignitable ammonia-air mixture is also important for ammonia-diesel dual-fuel ignition. Besides, an optimal SOI is needed to maximize the promoting effect of ignited fuel on ammonia combustion, and the optimal SOI changes with the ammonia energy fraction. Flame images confirm that the weightiness of the auto-ignition and flame propagation changes with the SOI, and the auto-ignition kernels gradually reduce and flame propagation plays a more and more important role as the SOI advances. At high loads, knocking combustion will also occur for ADDF engines, although the knock intensity is low. Besides, due to the enhancement effect of the knocking pressure wave, the flames show a strong white light at the knocking onset. The current results can help understand the combustion process and thus find the optimization method of ADDF engines.

Study on the formation and ignition law of ignition core in ammonia atmosphere diesel cylinder

Ammonia fuel does not contain carbon and is a kind of very good zero-carbon alternative fuel for diesel engines. However, ammonia is difficult to be ignited in diesel engine. The dual-fuel combustion mode of ammonia and diesel is an effective technical means to solve the problem. In this paper, the 186FA diesel engine test bench was built, and the ammonia/diesel dual fuel combustion mode was formed by injecting 0 %, 10 %, 20 %, 30 %, 40 %, and 50 % ammonia into the inlet and direct injection of diesel into the cylinder. The in-cylinder pressure and heat release laws were measured and analyzed at 2700r/min, 25 % load and 75 % load. Based on the analysis of the oxidation in ignition process of ammonia gas and diesel, a computational fluid dynamics model of the ignition process was established. By comparing the temperature contour surface in the cylinder and the concentration contour surface of OH radical, the paper put forward the ignition core evaluation index suitable for diesel/ammonia dual fuel. The formation law of the ignition core of diesel injected in homogeneous low reactive ammonia atmosphere in the cylinder was analyzed, and the influence of ammonia on the ignition process of diesel was revealed. The results show that the ignition delay period is prolonged after adding ammonia, and there is an exponential function relationship between the ignition delay period and the atmospheric concentration of ammonia. At 1200 K, there is an obvious parabolic relationship between ammonia concentration and OH radical concentration. The ignition core area was increased with the increase of ammonia concentration. Compared with pure diesel mode, the single ignition core at 75 % load of 2700 r/min is 3.6 times larger at 50 % ammonia atmosphere concentration. The ignition core will move up the diesel bundle with the increase of ammonia concentration. The study of chemical reaction kinetics showed that the reaction NH3 + OH = NH2 + H2O displayed positive sensitivity when ammonia concentration was less than 10 % and negative sensitivity when ammonia concentration was more than 10 %. The difference in sensitivity is the reason why the phase of the maximum burst pressure in the 10 % ammonia atmosphere is slightly earlier.

An experimental study the cross spray and combustion characteristics diesel and ammonia in a constant volume combustion chamber

Recently, the use of ammonia, a carbon-free fuel, in internal combustion engines, particularly in dual fuel dual direct injection engines, has attracted wide attention. However, the spray and combustion characteristics of diesel and ammonia dual direct injection especially on cross injections remain unclear. An optical study of diesel and ammonia spray and combustion was conducted using a constant-volume combustion chamber. The results revealed that spray tip penetration (STP) and spray projected area (SPA) of ammonia are lower than those of diesel, indicating that ammonia has a higher evaporation rate and a smaller diffusion rate than diesel. Besides, diesel and ammonia atomization was promoted through cross injection and collisions. As the cross injection interval increased, the liquid-phase STP of the collision spray increased, and its liquid-phase SPA decreased, while its vapor-phase SPA increased, promoting the diffusion and evaporation rates of the collision spray. In addition, increasing the interval of diesel and ammonia injection can shorten the ignition delay, and increase the flame lift-off length, leading to a more intense combustion process and less soot emissions. Therefore, the combustion and emission characteristics can be effectively improved by adjusting the injection timing of the two fuels reasonably.

RCCI combustion of ammonia in dual fuel engine with early injection of diesel fuel

Ammonia has gained considerable attention as a valuable, carbon-free alternative fuel for internal combustion engine (ICE) applications. The growing interest in ammonia's potential as an energy source stems primarily from its advantageous storage and transport properties. The reactivity-controlled compression ignition (RCCI) combustion mode presents a promising avenue for overcoming the challenges intrinsic to conventional diesel engines, such as elevated nitrogen oxides (NOx) and particulate matter (PM) emissions. Additionally, it addresses the limitations of both homogeneous charge compression ignition (HCCI) combustion (limited operational range) and premixed charge compression ignition (PCCI) combustion (diminished power output). The application of an ammonia-based RCCI combustion strategy emerges as a viable pathway for harnessing ammonia as a fuel. In this study, a numerical simulation on a single-cylinder heavy-duty engine operated in RCCI mode is conducted utilizing ammonia and diesel as fuels. The engine is operated at medium load and 910 RPM. The simulation results are validated against experimental data sourced from existing literature. The study investigates the impact of varying ammonia energy fractions, injection timing, and intake valve close temperature (TIVC) on key operational characteristics of the engine including in-cylinder pressure, heat release rate (HRR), combustion efficiency (CE), indicated mean effective pressure (IMEP), and emission levels. The results indicated that increasing the ammonia energy fraction within the RCCI combustion mode, transitioning from 30 % to 70 %, leads to a notable enhancement in IMEP, while maintaining low levels of carbon monoxide (CO), hydrocarbons (HC), unburned ammonia, and nitrous oxide (N2O) as greenhouse gases (GHG). Furthermore, increasing ammonia's energy fraction yielded a discernible reduction in NOx emissions and carbon dioxide (CO2). Conversely, the RCCI combustion mode attained superiority over the dual fuel combustion mode by simultaneously elevating CE and diminishing emissions of GHG, (CO2 and N2O) as well as unburned NH3.

Optimization of Combustion Cycle Energy Efficiency and Exhaust Gas Emissions of Marine Dual-Fuel Engine by Intensifying Ammonia Injection

The capability of operational marine diesel engines to adapt to renewable and low-carbon fuels is considered one of the most influential methods for decarbonizing maritime transport. In the medium and long term, ammonia is positively valued among renewable and low-carbon fuels in the marine transport sector because its chemical elemental composition does not contain carbon atoms which lead to the formation of CO2 emissions during fuel combustion in the cylinder. However, there are number of problematic aspects to using ammonia in diesel engines (DE): in-tensive formation of GHG component N2O; formation of toxic NOx emissions; and unburnt toxic NH3 slip to the exhaust system. The aim of this research was to evaluate the changes in combustion cycle parameters and exhaust gas emissions of a medium-speed Wartsila 6L46 marine diesel engine operating with ammonia, while optimizing ammonia injection intensity within the limits of Pmax, Tmax, and minimal engine structural changes. The high-pressure dual-fuel (HPDF) injection strategy for the D5/A95 dual-fuel ratio (5% diesel and 95% ammonia by energy value) was investigated within the liquid ammonia injection pressure range of 500 to 2000 bar at the identified optimal injection phases (A −10° CAD and D −3° CAD TDC). Increasing ammonia injection pressure from 500 bar (corresponding to diesel injection pressure) in the range of 800–2000 bar determines the single-phase heat release characteristic (HRC). Combustion duration decreases from 90° crank angle degrees (CAD) at D100 to 20–30° CAD, while indicative thermal efficiency (ITE) increases by ~4.6%. The physical cyclic deNOx process of NOx reduction was identified, and its efficiency was evaluated in relation to ammonia injection pressure by relating the dynamics of NOx formation to local combustion temperature field structure. The optimal ammonia injection pressure was found to be 1000 bar, based on combustion cycle parameters (ITE, Pmax, and Tmax) and exhaust gas emissions (NOx, NH3, and GHG). GHG emissions in a CO2 equivalent were reduced by 24% when ammonia injection pressure was increased from 500 bar to 1000 bar. For comparison, GHG emissions were also reduced by 45%, compared to the diesel combustion cycle.

Advancing RCCI engine performance via optimal acetylene premix ratios and advanced diesel injection timing: An experimental investigation

AbstractReactivity controlled compression ignition (RCCI) stands out as an innovative combustion strategy, effectively reconciling stringent emission regulations with precise combustion management and optimal engine performance. In this research, the influence of injection timing of diesel, acting as highly reactive fuel (HRF), alongside variable premix ratios of acetylene, a low reactive fuel (LRF), operating within the RCCI framework has been investigated. In a first‐of‐its‐kind attempt, with a thorough experimental design, the present investigation encompasses a progressive advancement of HRF injection timing, extending up to 110° CA bTDC with 20° CA increments, coupled with LRF integration at premix ratios of up to 70%. Optimal operational conditions materialize at an HRF injection timing advancement of 90° CA bTDC, complemented by a 40% LRF contribution. This configuration yields substantial gains, including a 28.2% upsurge in the cylinder pressure and an 18.6% elevation in the cylinder temperature compared to conventional diesel (CDC) operations. Additionally, the combustion process exhibits an advanced start of combustion (SoC) relative to the CDC baseline, with an 8.53% decline in heat release rate, at 40% LRF enrichment. Under optimal circumstances, moderate hydrocarbon (HC) emissions are noted, while smoke emissions experience a noteworthy reduction of 55.9%, all the while upholding overall output performance. A remarkable 69.8% peak increase in brake thermal efficiency is attained, underscoring the merits of judiciously advancing HRF injection timing and extending LRF utilization within the RCCI paradigm. Thus, the study underscores the synergistic potential between augmented HRF injection timing and controlled LRF integration, offering a promising avenue for elevating the RCCI approach.

Split injection strategies for a high-pressure hydrogen direct injection in a small-bore dual-fuel diesel engine

Hydrogen-diesel dual direct-injection (H2DDI) engines present a promising pathway towards cleaner and more efficient transportation. In this study, hydrogen split injection strategies were explored in an automotive-size single-cylinder compression ignition (CI) engine, with a focus on varying the injection timings and energy fractions. The engine was operated at an intermediate load with fixed combustion phasing through adjustments of pilot diesel injection timing. An energy substitution principle guided the variation in energy fraction between the two hydrogen injections and then diesel injection while keeping the total energy input constant. The findings demonstrate that early first hydrogen injection timings lead to characteristics indicative of premixed combustion, reflecting a high homogeneity of the hydrogen-air mixture. In contrast, hydrogen stratification levels were predominantly influenced by later second injection timings, with mixing-controlled combustion behaviour apparent for very late injections near top dead centre or when the second hydrogen injection held high energy fractions, which led to decreased nitrogen oxides (NOx: NO and NO2) emissions. The carbon dioxide (CO2) emissions did not show high sensitivity to the hydrogen split injection strategies, exhibiting about 77 % reduction compared to the diesel baseline due primarily to increased hydrogen energy fraction of up to 90 %.

An optical study on the cross-spray characteristics and combustion flames of automobile engine fueled with diesel/methanol under various injection timings

The fundamental research on the spray and combustion characteristics of diesel/methanol dual injection was explored in this study. A constant-volume combustion chamber was modified to accommodate cross-fuel injection by adding another fuel supply and an injection system. The effects of diesel/methanol injection timings on cross-spray and flame development were analysed for various injection intervals and pressures. The results showed that as the injection pressure increased, the high atomisation of the diesel–methanol mixed spray plume promoted its combustion. After diesel–methanol impingement at injection pressure of 100 MPa, a significant increase in the spray area occurred up to 62.5 % compared to its value at 60 MPa, resulting in a shortened combustion ignition delay, increased flame lift-off length and reduced soot generation. In addition, when methanol was used prior to diesel injection, the combustion ignition delay and flame lift-off length increased and soot generation decreased, as the diesel injection timings delay increased. Soot generation can be reduced by up to 33.3 % compared to that generated via the simultaneous injection of diesel/methanol at 60 MPa, by utilising a high injection pressure and proper injection timing. The study findings will provide a theoretical basis for the development of diesel/methanol dual-fuel direct-injection engines.

Impact of spray interaction on ammonia/diesel dual-fuel combustion and emission under engine relevant conditions

This study investigates the combustion characteristics of ammonia and diesel sprays in a constant-volume vessel under conditions typical of internal combustion engines, focusing on the interplay between evaporation dynamics and flame interactions within the framework of the Direct Dual Fuel Stratification (DDFS) concept. Under non-evaporation conditions, ammonia and diesel sprays exhibit comparable evaporation profiles, but under evaporation scenarios, ammonia’s higher evaporation rate results in faster mixing with ambient gas than diesel despite the similar liquid penetration lengths of these two fuels. By utilizing meticulously designed arrangements of diesel and ammonia spray injectors, two distinct interaction scenarios between diesel spray and ammonia spray, early and late interaction, are explored. In the early interaction scenario, fuel-rich ammonia-air mixtures ignite directly by the diesel flame, achieving self-sustained propagation and significant heat release, thereby maintaining a high-temperature region for continuous combustion. Conversely, in late interaction scenarios, rapid ammonia evaporation leads to a fuel-lean ammonia/air mixture that cannot be ignited by the diesel flame, eventually leading to ammonia flame extinction. The study reveals that NOx and N2O emissions are sensitive to the diesel/ammonia flame interaction. N2O emissions, formed predominantly at the forefront of the quenching ammonia flame, pose a significant challenge due to the fast evaporation rate and slow oxidation rate in fuel-lean mixtures. These findings provide insights into the physics of ammonia–diesel combustion, highlighting the challenges and potential strategies for efficient and clean combustion in ammonia-fueled DDFS engines.

Effects of diesel injection timing and methanol substitution ratio on combustion and exhaust emission characteristics of a dual fuel compression ignition engine

Effects of diesel injection timing and methanol substitution ratio on combustion and exhaust emission characteristics of a dual fuel compression ignition engine

Enhancing ammonia engine efficiency through pre-chamber combustion and dual-fuel compression ignition techniques

In pursuit of unleashing ammonia’s potential in internal combustion engines, an extensive computational study was conducted to explore the effects of two advanced combustion techniques: pre-chamber combustion (PCC) and dual-fuel compression ignition (DF−CI) on a heavy-duty ammonia engine. In the PCC mode, hydrogen was introduced into the pre-chamber (PC) to generate distributed reacting jets, with a small energy fraction of 0.5%. The case featuring a slightly narrower PC throat (diameter of 5.4 mm) yielded the highest indicated thermal efficiency (ITE) of 50.4%, owing to the rapid distribution of reacting jets and advanced combustion phasing. Further increase in hydrogen energy fraction and reduction in throat diameter resulted in a lower ITE because of the enhanced wall heat transfer loss. The DF−CI mode also exhibited significant potential for achieving high efficiency. Through a systemic optimization of parameters such as diesel injection timing, spray included angle, injection pressure, swirl ratio, and piston shape, a significantly enhanced ITE of 50.3% was attained, 7.2% higher than the baseline scenario. The improvement was primarily attributed to the promoted mixing of diesel with air. Among the design parameters, the swirl ratio and spray included angle exhibited the most significant impact on the engine performance. Overall, both the PCC and DF−CI modes were found to yield high ITE and low ammonia emissions. However, because 20% of the diesel energy fraction was utilized to mitigate ammonia slip in the DF−CI mode, notably higher greenhouse gas emissions (carbon dioxide of 96 g/kW-h) were generated than in the PCC mode. In this regard, the ammonia-hydrogen PCC mode should be a more promising solution to achieve zero-carbon emissions for future ammonia engines.

Numerical analysis and optimization of combustion and emissions in an ammonia-diesel dual-fuel engine using an ammonia direct injection strategy

To reduce greenhouse gases in accordance with stringent emission regulations, interest in ammonia, a carbon-free fuel, is increasing in the heavy-duty engine industry. Pre-mixed ammonia-diesel dual-fuel combustion showed better results than diesel combustion in efficiency and greenhouse gas emissions, but NO and unburned NH3 levels were significant. Therefore, a liquid ammonia direct injection strategy should be considered, and that requires detailed combustion and emission formation process analyses. Therefore, in this study, a numerical analysis of the direct injection ammonia-diesel combustion process was conducted, and an optimal injection strategy was sought. Compensating for the slow flame speed of ammonia by supplying additional momentum to the ammonia through direct injection could improve combustion characteristics. Furthermore, NO removal could be promoted by widening the thermal DeNOx reaction region compared to that in pre-mixed ammonia-diesel combustion. At injection timing was −7 CAD for the ammonia injection and −15 to −10 CAD for the diesel injection, the efficiency increased by 8 %, NO emissions were reduced by up to 13.5 %, and GHG emissions were reduced by about 91 % compared with diesel alone. In addition, unburned ammonia was reduced to least 58.4 ppm, a significant improvement over pre-mixed ammonia combustion.

Study on the impact mechanism of ammonia energy fraction on in-cylinder combustion and pollutant generation under wide operation conditions of medium-speed diesel engines

To expedite the utilization of ammonia in the domain of marine medium-speed diesel engines. The computational fluid dynamics (CFD) model combined with the ammonia/n-dodecane reaction mechanism were conducted to explore the impact mechanism of ammonia energy ratio (AER) and diesel injection timing on in-cylinder combustion and pollutant emission at low-mid-high loads of marine medium-speed diesel engines. Further, the formation laws of Thermal and Fuel nitrogen oxides (NOX) at various AER conditions were analyzed. At 10 % load, the rising AER advanced the CA50 by 57 % and increased the in-cylinder peak pressure by 3.5 % due to the enhanced premixed combustion stage. Whereas, at higher loads (50 % & 100 %), the effect of high specific heat capacity of ammonia played a crucial role in combustion progress with the increasing AER, which reduced the in-cylinder peak pressure by 1–3 %. The sensitivity of key combustion phases (CA10-CA90) to AER also gradually decreased with the rising loads because of the inhibited diffusion combustion stage. When the IT was 6°BTDC, the peak temperature in the cylinder decreased by 10 % at 10 % engine load; and the charge of excessive temperature in the cylinder was significantly reduced at 50 % and 100 % engine load. In terms of emission characteristics, HC and CO emission significantly reduced when AER was 45 %. And the proportion of Fuel NH3 in the fuel rose from 75.5 % to 91.4 % with the increasing AER. This means that the generation conditions of Thermal NOx were inhibited in the large proportion of ammonia-doped combustion conditions.

Measurements and analyses on the two-phase fuel transient flow characteristics of dual fuel co-direct injector

In this research, an innovative two-phase fuel transient flow coefficient measurement system is proposed to investigate the flow characteristics and coupling effects of two-phase fuel, and to fill the gap of the two-phase fuel flow characteristics measurement technology of dual fuel injector. For this purpose, microphotography technology is used to obtain the original image of the injector hole, and the accurate area of the injector hole can be obtained by image processing. The two-phase injection momentum and the transient injection pressure are measured by the impact force sensor and the pressure sensor respectively, and the two-phase fuel transient flow coefficient is obtained. Due to the change of the increasing rate of the effective flow area at the nozzle, the gas transient flow coefficient shows two different increasing trends during the upward stage of the gas needle valve. With the background pressure increase, the maximum gas transient flow coefficient decreases and injection duration increases. The influence of pilot diesel injection on subsequent gas injection stages is mainly reflected in that when the gas energizing time is 0.8 ms, the fluctuation range of gas mass flow caused by diesel injection is 52.6%, and the fluctuation range is 14.9% when the gas energizing time is 2 ms, but the influence of diesel injection on the peak value of gas transient flow coefficient can be ignored.