Advanced Diesel Research Articles

The role of charge reactivity in ammonia/diesel dual fuel combustion in compression ignition engine

This study investigates the combustion characteristics of diesel–NH3–air mixture in compression ignition engine. Three different levels of ammonia energy ration (AER) were used for the investigation: 0 % AER (pure diesel), 30 % AER, and 50 % AER. Increasing AER leads to a rise in the initial peak of apparent heat release rate and promotes the prevalence of premixed combustion. Numerical simulations effectively capture the abrupt increase in maximum cylinder pressure (Pmax) from 7.4 to 7.9 MPa as AER increases from 0 to 30 %. Additionally, raising AER from 0 to 30 % extends a high-temperature region externally in the squish zone, attributed to the higher knocking propensity of the 30 % AER premixed charge. The ammonia-assisted diesel accomplish advanced diesel direct injection timing (SOID) at both heavy and medium load conditions. Under light load conditions, an increase in ITE is observed for AER = 50 % as SOID varies from −4 °CA to −10 °CA (ATDC). For medium and high load conditions, ITE monotonically increases with advancing SOID. The maximum ITE of 44.5 % is achieved at SOID = −12 °CA (ATDC) and AER = 30 %.

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.

Co-optimization of injection parameters and injector layouts for a methanol/diesel direct dual-fuel stratification (DDFS) engine

Direct dual fuel stratification (DDFS) is a promising combustion mode to achieve satisfactory engine performance with the effective control of ignition and combustion processes. In this study, a DDFS engine fueled with methanol and diesel was investigated at low loads based on a four-stroke light-duty naturally aspirated engine. Both injection parameters and injector layouts of the two fuels were co-optimized by the fast nondominated sorting genetic algorithm (NSGA-II). The results show that the fractions, injection timings, spray half-included angles, and injector positions of the two fuels all showed significant influences on engine performance. Finally, the high methanol fraction, advanced diesel injection timing, methanol injection timing near the top dead center, and large spray half-included angle of methanol were adopted in the optimal case to achieve both low EISFC and NOx simultaneously. Meanwhile, a centrally-mounted methanol injector was beneficial to shorten combustion duration, and the diesel injector can be arranged in a semicircle area with a radius of approximately 1.14 cm to provide the sufficiently high temperature for the complete combustion of methanol.

Reduced commuter exposure to PM2.5 and PAHs in response to improved emission standards in bus rapid transit systems in Mexico

We evaluated impacts of progressive technological updates to bus rapid transit (BRT) systems on in-cabin concentrations of particulate matter with an aerodynamic diameter ≤2.5 μm (PM2.5), and the various polyaromatic hydrocarbons (PAHs) to which commuters were exposed. PM2.5 samples were collected and real-time concentrations measured from October 2017 to March 2020 inside cabins of BRT buses equipped with Euro IV, V and VI diesel emission standards in the Mexico City Metropolitan Area (MCMA). For effective comparison, similar samplings and measurements were carried out on trains in the MCMA underground (MCU) system. Peak in-cabin PM2.5 concentrations decreased significantly (p < 0.05) by 35% from Euro IV to Euro V buses, and by 80% from Euro IV to Euro VI buses. PM2.5 concentrations inside Euro VI buses were significantly lower (p < 0.05) than in Euro IV and Euro V buses and in underground trains. The in-cabin excess (ICE) of PM2.5 relative to ambient concentrations was significantly (p < 0.05) higher for Euro IV than for Euro V buses during morning the traffic peak, and consistently higher than for Euro VI buses. Indeed, ICEs calculated for Euro VI buses were always lower than those for electricity-powered underground trains. The frequency of hotspots decreased from Euro IV to Euro VI buses due to the combined effect of low emissions and closed, air-conditioned cabins. Concentrations of total PAHs including carcinogenic species also decreased from Euro IV to Euro V buses and were below limits of detection aboard Euro VI buses. This work shows that in real-life conditions, advanced diesel technologies and cabin design significantly reduce commuters’ exposure to PM2.5 and to toxic PAH compounds.

Electric Hybrid Powertrain for Armored Vehicles

The performance of modern, new generation-armored vehicles would greatly benefit from overall engineering, optimization, and integration techniques of advanced diesel engines-electrified transmissions. Modern axial flux electric motors and controllers are perfectly able to replace the classical automatic gearbox and complex steering system of traditional Main Battle Tanks. This study shows a possible design of a serial hybrid electric power pack for very heavy tanks with a weight well over 50 tons. The result is a hybrid power system that improves the overall performance of armored vehicles off-road and on-road, improving the acceleration and the smoothness of the ride. In addition, fuel consumption will be reduced because the internal combustion engine operates at fixed rpm. The electric motors will outperform the traditional engines due to their very high torque output even at “zero speed”. The weight of a hybrid system has also been calculated. In fact, in many cases, it is possible to use all off-the-shelf components. The on-board diagnosis of the subsystems in the hybrid powertrain makes it possible to achieve a Time Between Overhaul (TBO) of 4500 h with a failure probability inferior to one in 10,000.

Application of Model-Based Controller on a Heavy-Duty Dual Selective Catalytic Reduction Aftertreatment

&lt;div&gt;Commercial vehicles require advanced engine and aftertreatment (AT) systems to meet upcoming nitrogen oxides (NO&lt;sub&gt;x&lt;/sub&gt;) and carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) regulations. This article focuses on the development and calibration of a model-based controller (MBC) for an advanced diesel AT system. The MBC was first applied to a standard AT system including a diesel particulate filter (DPF) and selective catalytic reduction (SCR) catalyst. Next, a light-off SCR (LO-SCR) was added upstream of the standard AT system. The MBC was optimized for both catalysts for a production engine where the diesel exhaust fluid (DEF) was unheated for both SCRs. This research shows that the tailpipe (TP) NO&lt;sub&gt;x&lt;/sub&gt; could be reduced by using MBC on both catalysts. The net result was increased NO&lt;sub&gt;x&lt;/sub&gt; conversion efficiency by one percentage point on both the LO-SCR and the primary SCR. The CO&lt;sub&gt;2&lt;/sub&gt; emissions were slightly reduced, but this effect was not significant. Finally, the MBC was used with a final setup representative of future AT systems which included standard insulation on the catalysts and optimal DEF dosing controls. This final configuration resulted in an improved NO&lt;sub&gt;x&lt;/sub&gt; and CO&lt;sub&gt;2&lt;/sub&gt; such that the composite Federal Test Procedure (FTP) NO&lt;sub&gt;x&lt;/sub&gt; was 0.060 g/hp-hr and the composite FTP CO&lt;sub&gt;2&lt;/sub&gt; was 508.5 g/hp-hr. The article details this cycle along with the low-load cycle (LLC) and beverage cycle. More technologies are required to meet the future California Air Resources Board (CARB) 2027 standard, which will be shown in future work.&lt;/div&gt;

Effects of piston shape and nozzle specifications on part-load operation of natural gas–diesel dual-fuel RCCI engine and its application to high load extension

• Effects of piston shape and multi-angle nozzle were evaluated for DF RCCI operation. • Enhanced air utilization w/multi-angle nozzle reduced combustion and HT losses. • The highest GIE of RCCI improved as 51.8 % by hardware modifications. • Intake air amount could be increased by lowering CR (from 17 to 15) at the maximum load. • The maximum load of RCCI could be extended from 81 (reference) to 101 kW of BP. In this study, the effects of modifications of both the piston shape and injector nozzle are experimentally investigated for high load extension of a natural gas–diesel dual-fuel reactivity-controlled compression ignition (RCCI) engine. First, a bathtub shape with a reduced compression ratio is applied to the modified piston which was reported to improve the flame propagation in squish volume, the cooling loss, and the air induction rate under the same limit of in-cylinder pressure from previous studies. In addition, a multiangle two-layer injector is used to extend the maximum load, which has been proven to be effective for unburned hydrocarbon emissions and gross indicated efficiency in part-load operation in our previous study. The experiments are conducted under both 1200 rpm part-load operation (approximately 1950 J/cylinder per cycle of fuel input energy) and 1800 rpm maximum load operation. The objectives are to comprehensively evaluate the effects of the modifications on natural gas–diesel RCCI operation and verify the effects of all load conditions. The experimental results reveal that the changes in the piston—reduction in the compression ratio and a bathtub piston shape—are effective for both NOx and smoke emissions as the diesel injection timing is advanced. Although the multi-hole double layer (combined narrow and wide injection) has less effect on emissions compared to that of the change in piston, it affects the mixing process inside the cylinder, thus retarding the combustion phasing, prolonging the combustion duration, and eventually reducing the cooling loss. Both modifications are highly effective for advanced diesel injection timing corresponding to RCCI operation, which extends high-load operation from 80.9 to 101 kW of brake power, relatively 24.8 % increase, by adopting both the piston and injector modifications. Based on the modifications, the mass fraction of natural gas is suggested to be approximately 80 %. A higher fraction causes the variation in the maximum in-cylinder pressure to be extremely sensitive to allow robust operation. In contrast, if it is lower, the amounts of both NOx and smoke emissions exceed the emission standard levels (0.4 g/kWh and 15 mg/kWh for NOx and smoke emissions, respectively, corresponding to Stage-V of non-road engine operation).

Experimental investigation on operating light-duty diesel engine using ethanol–gasoline blends in a homogeneous charge compression ignition combustion mode

The advanced diesel combustion mode of homogeneous charge compression ignition (HCCI) provides simultaneous lessening of soot and oxides of nitrogen (NOx) emissions. However, HCCI operations with low volatility and high reactivity diesel fuel require energy-intensive vaporizers and suffer from a restricted operating load range. In this work, high volatility, and low reactivity ethanol–gasoline blends were utilized as fuels in a port fuel injected light-duty diesel engine operated in HCCI mode to address this limitation. To study the effect of adding ethanol to the test fuels, its content was progressively increased from 10% to 60% by simultaneously reducing the gasoline content. 6% of an ignition improver, 2-ethylhexyl nitrate (2-EHN), was added to test fuels to attain stable HCCI combustion in the test engine at lower engine loads. A combined experimental and statistical approach was followed to characterize the HCCI engine combustion, performance and emissions. The impact of independent operating factors of ethanol–gasoline fuel blend composition and engine load on the various response parameters was estimated using multi-regression models developed based on the response surface method (RSM). The optimization of engine parameters was performed using the desirability approach of RSM to maximize performance and minimize emissions. The engine operating load range was extended from 23% (1.22 bar BMEP) to 86% (4.63 bar BMEP) with ethanol–gasoline–2-EHN-fuelled HCCI, which was a substantial improvement over the achievable load range only up to 38% (2.02 bar BMEP) with diesel-fuelled HCCI. All the multi-regression models developed were statistically significant at a 95% confidence level. The results showed that the indicated thermal efficiency improved, and soot and NOx emissions reduced with increased ethanol content in the test fuels. The test engine showed optimal working conditions when operated using 49% ethanol in the test fuels at 75% engine load. To benchmark the HCCI engine performance under optimal operating conditions, it was compared with conventional diesel combustion at 75% engine load. The NOx and soot emissions decreased by 76% and 98%, respectively, while indicated thermal efficiency increased by 20% for HCCI than conventional mode. The optimal fuel reactivity was determined at various engine loads by using the model equation developed for combustion phasing. According to the findings of this study, the fuel management strategy of using ethanol and gasoline blends is a viable method to enhance the performance and emission metrics of HCCI engines.

A numerical study on the effects of bowl and nozzle geometry on performances of an engine fueled with diesel or bio-diesel fuels

Abstract One of the most important trends for advanced diesel engines is downsizing, i.e., higher power density, which means more fuel is burned in a shorter period. In order to achieve rapid combustion for a high-power density diesel engine, the effects of bowl shape, diameter-to-depth ratio of bowl, and arrangement of nozzle holes on combustion and performance were investigated by CFD simulation. The effects of four bowl shapes, two of which were double-layer split bowls (DLSBs), as well as four diameter-to-depth ratios and three arrangements of nozzle holes were numerically assessed. The results show that the DLSB with a shallow dish-like structure yielded a remarkable effect of swirling flow by fuel splitting into upper- and lower-layer zones, which improved fuel–air mixing, shortened combustion duration, thus, resulting in high combustion efficiency and power density. Moreover, with the increase in diameter-to-depth ratio of the B type DLSB, the turbulent kinetic energy and the peak of pressure and heat release rate increased, further increasing power density. Finally, when the DLSB with a diameter-to-depth ratio of 2.0 is coupled with the staggered double-layer arrangement of nozzle holes, the in-cylinder mixtures became more uniform at both the circumferential and radial directions, and the combustion was considerably accelerated, achieving an optimum specific power of 122.6 kW·L−1. Meanwhile, there was a slight decrement for peak pressure and NOx emission, and smoke decreased by 49.1%, which revealed substantial improvement in reduction in mechanical load and emissions.

Life Cycle Cost Analysis of Ashore Marine Engine Room

This paper aims to present a method for comparing decision options for the ashore marine engine room. Based on the life cycle cost system, the life cycle stages are divided into design, acquisition, installation, operation, maintenance, and scrapping. A model of the life cycle cost of ashore marine engine room considering the time value of money was developed, and a calculation method for sensitivity analysis was developed. Regarding the actual case, the life cycle cost of the two options was estimated, the sensitivity of the cost of the two options was analyzed, and control recommendations were made. The results show that Option 2, with the highest initial investment, is the optimal solution, attributed to using an advanced two‐stroke diesel engine with reduced operation and maintenance costs. This will be useful for reference by maritime academies.

NOx Emission of a Correlation between the PEMS and SEMS over Different Test Modes and Real Driving Emission

The aim of this study is to verify the reliability of NOx emissions measured using Smart Emissions Measurement System (SEMS) equipment in comparison with the NOx emissions measured using certified Portable Emissions Measurement System (PEMS) equipment. The SEMS equipment is simple system, and it is less expensive than the PEMS equipment, as it comprises an On-Board Diagnostics (OBD) signal from the test vehicle and a NOx sensor. The SEMS equipment based on low-cost sensors has an advantage of building big data, but there are insufficient previous studies comparing of NOx emissions with certified the PEMS equipment. Therefore, this study is important in verifying the suitability of the SEMS equipment by comparing the NOx emissions measured by the various test modes and RDE using the two types of equipment. To analyze the correlation between the PEMS and SEMS equipment, the advanced diesel vehicle was equipped with the two types of equipment to simultaneously measure NOx emissions. After installing the equipment on the test vehicle, it was conducted under various test modes in the laboratory and the Real Driving Emission (RDE) test to verify the correlation of NOx emissions measured by the SEMS equipment. The correlation analysis for the NOx emissions measured by the PEMS and SEMS equipment under various test conditions and the RDE test indicated that the slope of the NOx emissions was approximately equal to 1, and the coefficient of determination was 0.9 or higher. Based on these test results, it was concluded that NOx emissions measured by the PEMS and SEMS equipment are highly similar.

Combustion Phenomena and Emissions in a Dual-Fuel Optical Engine Fueled with Diesel and Natural Gas

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The application of dual-fuel combustion in the freight transportation sectors has received considerable attention due to the capability of achieving higher fuel efficiency and less pollutant emissions than the conventional diesel engines. In this study, high-speed flame visualization was used to investigate the phenomena of natural gas/diesel dual-fuel combustion in a single-cylinder heavy-duty engine with optical access. To implement diverse fuel blending conditions, diesel injection timing and natural gas substitution ratio were varied under constant fuel energy input. A novel flame regime separation method was implemented based on color segmentation in HSV color space to characterize the spatial distributions of premixed and non-premixed flame regimes. Flame images for larger natural gas substitution showed a significant reduction in the non-premixed flame regime accompanied by flame propagation along the vaporized diesel sprays. Advanced diesel injection shifted the location of early flames toward the piston bowl wall and created a rapid influx of propagating flame. These changes in fueling parameters resulted in the reduction of soot radiation, which was verified by the particulate matter emissions measured in the performance engine test under identical operating conditions.&lt;/div&gt;&lt;/div&gt;

Parametric investigation on hydrogen driven homogeneous charge compression ignition mode with advanced diesel injection using chemical kinetics based numerical model

In the present study, a numerical model based on chemical kinetics was developed to investigate the effect of different parameters on characteristics of hydrogen diesel homogeneous charge compression ignition (HDHCCI) mode. The results showed that the combustion process was retarded with diminished cool flame as increasing hydrogen energy share (HES) due to reduction of H2O2, H2O and OH radicals with hydrogen addition. Thus, it increased the indicated thermal efficiency (ITE) and decreased the indicated specific energy consumption (ISEC). The levels of NOx and soot emissions were reduced by 22% and 63% at maximum HES. A spray angle of 10° decreased the total fuel impingement compared with a spray angle of 74° because of improvement in air-fuel mixing phenomena. Incomplete combustion was recovered at HES of 25% when increasing the charge temperature or adapting the twin-pulse in HDHCCI mode, consequently the ITE was improved with a decrease in ISEC.

An Eco-Efficiency Assessment of Bio-Based Diesel Substitutes: A Case Study in Thailand

The development of new bio-based diesel substitutes can improve their compatibility with diesel engines. Nevertheless, for actual implementation, their environmental and economic performance needs to be studied. This study quantified the eco-efficiency of three bio-based diesels, viz., fatty acid methyl ester (FAME), partially hydrogenated FAME (H-FAME), and bio-hydrogenated diesel (BHD), to address the perspective of producers as well as policymakers for implementing the advanced diesel alternatives. The eco-efficiency was assessed as a ratio of life cycle costing as the economic indicator and three different environmental damages—human health, ecosystem quality, and resource availability. The eco-efficiency of FAME was the most favorable among all the potential substitutes with regard to human health and ecosystem quality, but the least favorable for resource availability impact. Even though BHD was beneficial in terms of life cycle costing, it was the least preferable when considering human health and ecosystem quality, though it performed the best for resource availability. H-FAME was also promising, in line with FAME. It is suggested that the technologies for BHD production should be improved, especially the catalyst used, which contributed greatly to environmental impacts and costs.

A Study on the High Load Operation of a Natural Gas-Diesel Dual-Fuel Engine

Diesel fueled compression ignition engines are widely used in power generation and freight transport owing to their high fuel conversion efficiency and ability to operate reliably for long periods of time at high loads. However, such engines generate significant amounts of carbon dioxide (CO2), nitrogen oxides (NOx), and particulate matter (PM) emissions. One solution to reduce the CO2and particulate matter emissions of diesel engines while maintaining their efficiency and reliability is natural gas (NG)-diesel dual-fuel combustion. In addition to methane emissions, the temperatures of the diesel injector tip and exhaust gas can also be concerns for dual-fuel engines at medium and high load operating conditions. In this study, a single cylinder NG-diesel dual-fuel research engine is operated at two high load conditions (75% and 100% load). NG fraction and diesel direct injection (DI) timing are two of the simplest control parameters for optimization of diesel engines converted to dual-fuel engines. In addition to studying the combined impact of these parameters on combustion and emissions performance, another unique aspect of this research is the measurement of the diesel injector tip temperature which can predict potential coking issues in dual-fuel engines. Results show that increasing NG fraction and advancing diesel direct injection timing can increase the injector tip temperature. With increasing NG fraction, while the methane emissions increase, the equivalent CO2emissions (cumulative greenhouse gas effect of CO2and CH4) of the engine decrease. Increasing NG fraction also improves the brake thermal efficiency of the engine though NOx emissions increase. By optimizing the combustion phasing through control of the DI timing, brake thermal efficiencies of the order of ∼42% can be achieved. At high loads, advanced diesel DI timings typically correspond to the higher maximum cylinder pressure, maximum pressure rise rate, brake thermal efficiency and NOx emissions, and lower soot, CO, and CO2-equivalent emissions.

On the Variation of the Effect of Natural Gas Fraction on Dual-Fuel Combustion of Diesel Engine Under Low-to-High Load Conditions

Natural gas-diesel dual fuel (NDDF) engine has the potential to significantly reduce carbon dioxide (CO2) and particulate matter (PM) emissions, while retaining diesel engine’s high efficiency and reliability. The operation and performance of NDDF engine depend on natural gas energy fraction (%NG), which ranges from low %NG, where diesel fuel provides most of the combustion energy, to high %NG where diesel fuel is used only to initiate combustion. Although pertaining published studies demonstrated that the effect of %NG on the combustion performance and emissions of NDDF engine depend upon the engine load, none of these studies discussed the reasons behind this dependence. The present study attempts to shed light on this issue by experimentally and numerically investigating the effect of different %NGs on NDDF engine under different load conditions. Both experimental and numerical results revealed that the peak pressure rise rate (PPRR) first increases and then drops with increasing %NG under all load conditions. The calculated local equivalence ratio and charge temperature contours showed that increasing %NG to a certain limit increases local equivalence ratio inside the ignition kernel which implies that more premixed natural gas – air mixture participates in reactions during the premixed combustion stage. This results in an increased flame temperature and higher PPRR right after ignition. However, increasing %NG beyond this range decreases local equivalence ratio inside the ignition kernel which leads to lower PPRR. Increasing %NG retards the combustion phasing at low to medium load conditions. However, increasing %NG generally advances the combustion phasing under medium to high load conditions due to the fact that the flame propagation speed of natural gas – air mixture increases with %NG at medium to high load conditions. Methane emissions grow with increasing %NG under all examined engine load conditions. However, this growth becomes much smaller under medium to high engine load conditions. Increasing %NG significantly increases GHG emissions under lower load conditions. However, using advanced diesel injection timing decreases GHG emissions of NDDF engine under lower load conditions. Increasing %NG decreases GHG emissions by 6 to 11% under medium to high load conditions.

Influence of fuel injection pressure and injection timing on nanoparticle emission in light-duty gasoline/diesel RCCI engine

This work investigates the influence of fuel injection events on the nanoparticle emission characteristics of light-duty gasoline-diesel RCCI engine. The formation of nanoparticle emissions strongly depends on fuel injection events. The present study experimentally investigates the influence of diesel injection pressure, injection timing, and port-injected gasoline mass on the nanoparticles emitted from the gasoline-diesel RCCI engine. For this purpose, the engine is tested at different engine speeds and a fixed load of 1.5 bar BMEP without exhaust gas recirculation. The particle-size and number distribution (PSD) and total particle number (total PN) concentration are measured using a differential mobility spectrometer. The results depict that at higher diesel injection pressure (IP) operation, the peak of the NMP increases while the AMP peak decreases for neat diesel operation as well as RCCI engine. Nucleation, as well as accumulation mode particles, increases with advanced diesel injection timing in RCCI combustion. An increase in port fuel injected mass also leads to an increase in the total particle concentration and total unburned hydrocarbon (THC) emissions.

Cycle-to-Cycle Multipulse Fuel-Injection Control for Advanced Diesel Combustion in Changing and Disturbed Operating Points

Abstract When controlled in an open-loop fashion, both stationary and dynamical diesel engine performance can deteriorate due to disturbances. Although cycle-to-cycle fuel injection control has the potential of reducing the performance degradation by manipulating the fueling profile in real time, this potential has not been thoroughly studied. This is especially true for multipulse fuel injection, due to the lack of a controller design method with closed-loop reference tracking performance guarantees. In this paper, we introduce a systematic design method for multivariable cycle-to-cycle fuel injection control. The design method is based on several local linearizations to address varying combustion behavior due to different engine speeds, torques, and disturbances. This leads to a controller that is robust with respect to all the local linearizations. Experimental results show that the controller works well in both stationary and dynamical operating conditions, and has fast dynamical performance (settling time less than 1.5 (s)). Moreover, experimental data show that cycle-to-cycle fuel injection control is robust against the uncertainties introduced by disturbed rail pressure and swirl valve position.

Exploring the high load potential of diesel–methanol dual-fuel operation with Miller cycle, exhaust gas recirculation, and intake air cooling on a heavy-duty diesel engine

Legislations concerning emissions from heavy-duty diesel engines are becoming increasingly stringent. This requires conventional diesel combustion to be compliant using costly and sophisticated aftertreatment systems. Preferably, diesel–methanol dual-fuel is one of the suitable alternative combustion modes as it can potentially reduce the formation of nitrogen oxide and soot emissions which characterised the diesel mixing-controlled combustion. This is primarily due to the high latent heat of vaporisation and oxygen content of the methanol fuel. At high engine loads, however, the potential of diesel–methanol dual-fuel operation is constrained by the excessive combustion pressure rise rate and peak in-cylinder pressure, which limits both the engine efficiency and the percentage of methanol that can be used. For the first time, experimental studies were conducted to explore advanced combustion control strategies such as Miller cycle, exhaust gas recirculation, and intake air cooling for improving upon high load diesel–methanol dual-fuel combustion. Experiments were carried out at 1200 r/min and 18 bar indicated mean effective pressure on a single-cylinder heavy-duty diesel engine, which equipped with a high pressure common rail diesel injection, a methanol port fuel injection, and a variable valve actuation system on the intake camshaft. Results showed that the methanol energy fraction of a conventional diesel–methanol dual-fuel operation with a baseline intake valve closing timing was limited to 28%. This was due to the high combustion temperature at a high load which advanced the ignition timing of the premixed charge, resulting in high levels of pressure rise rate. The application of lower effective compression ratio and intake air temperature ( Tint) effectively decreased the compression temperature, which successfully delayed the ignition timing of the premixed charge. This allowed for a more advanced diesel injection timing to achieve improvement in the thermal efficiency and potentially enabled a higher methanol substitution ratio. Although the introduction of exhaust gas recirculation demonstrated very slight impact on the ignition timing of the premixed charge, a higher net indicated efficiency was observed due to a relatively lower local combustion temperature which reduced heat transfer loss. Moreover, the optimised diesel–methanol dual-fuel operation allowed a higher methanol energy fraction of 40% to be used at an effective compression ratio of 14.3 and Tint of 305 K and achieved the highest net indicated efficiency of 47.4%, improving by 3.7% and 2.6%, respectively, when compared to the optimised conventional diesel combustion (45.7%) and conventional diesel–methanol dual-fuel (46.2%). This improvement was accompanied with a reduction of 37% in nitrogen oxide emissions and little impact on soot emissions in comparison with the conventional diesel combustion.

Impacts of advanced diesel combustion operation and fuel formulation on soot nanostructure and reactivity

Advanced diesel combustion, accomplished via a single pulse fuel injection and high levels of exhaust gas recirculation (referred to as “PCCI”, partially-premixed charge compression ignition), is shown to be a path to reduce oxides of nitrogen and particulate matter simultaneously. This is well established in the literature. Less established is the extent to which such dilute combustion processes influence soot formation and affect soot that is emitted from diesel engines under such combustion modes. This work focuses on characterization of the nanostructure and oxidative reactivity of soot generated by a light-duty turbodiesel engine operating under a PCCI combustion mode, a dilute, low-temperature combustion process. Previous work on a type of PCCI combustion, referred to as high-efficiency clean combustion (HECC), showed soot samples having a fullerenic nanostructure, characterized by high levels of tortuosity of the fringe layers as seen in transmission electron micrograph images and as quantified using an image processing algorithm. Thermogravimetric analysis of the HECC mode soot samples showed that they displayed higher rates of oxidation than soot samples from a conventional diesel combustion mode. The present work returns to PCCI combustion, considering the timing of the main fuel injection, and the effects of operating on fuels rich in n-alkanes, particularly a fuel produced from a low temperature Fischer-Tropsch process (LTFT) and a renewable diesel fuel (RD) produced via hydrodeoxygenation of a plant oil. PCCI combustion conditions yield soot that shows higher reactivity compared to soot from the conventional combustion mode regardless of fuel type. LTFT and RD fuels produce soots with lower reactivity compared to ULSD. Soots produced from PCCI combustion have higher surface oxygen concentration and higher proportion of amorphous carbon. In addition, TEM images show that PCCI soots from all three fuels have smaller primary particle and particle aggregate sizes, and smaller graphene layers. These properties explain the higher reactivity of soot from PCCI combustion. The less reactive soots, which are produced from LTFT and RD fuel under conventional combustion, show internal burning during oxidation. However, soots with higher reactivity which are produced from late injection PCCI combustion and ULSD show shrinking core oxidation, likely because of their overall amorphous structure.