Low Engine Load Research Articles

Comprehensive analysis of particle emissions from miniature turbojet engine

Emission of particulate matter from jet engines contribute to deterioration of air quality in the vicinty of the airports and to formation of contrails in higher layers of the atmosphere. This article presents the results of the measurements of particle emissions from a miniature jet engine GTM-120 fueled conventional aviation fuel Jet A-1. Analysis of particle size distribution, number, mass and volume emission indexes has been made, as well as the analysis of the emission intenisty and mass emission rate. Obtained results were related to LTO cycle phases. The results shows, that the particle number concentration was the lowest for low engine loads, with characteristic diameter of 69.8 nm and the particles concentration of 7.7 x 106 particles/cm3. For thrust increase, the characteristic diameter is smaller, and the particles distribution is no longer single-mode. The highest particles concentration for cm3 is for 100% thrust and is equal to 1.55 x 107 particles, with characteristic diameter of 34 nm.

Role of the Compression Ratio in Dual-Fuel Compression Ignition Combustion with Hydrogen and Methanol.

Renewable hydrogen and e-fuels, synthesized from captured CO2 and renewable H2, are feasible ways to achieve transport decarbonization, particularly in medium/heavy-duty applications and the maritime sector, where compression ignition engines predominate. Hydrogen and methanol are low carbon-intensive fuels, which can be used in these engines by carrying out dual-fuel combustion with a diesel-like fuel. Under low load engine conditions, reaching very high substitutions of the fossil diesel fuel can be a major challenge as the presence of these fuels affects negatively the autoignition process. Therefore, this work explores the substitution limits in dual-fuel mode with hydrogen and methanol under low load conditions (5.2 bar IMEP) for two different compression ratios (15.84:1 and 18.04:1) using a 1.13 L single-cylinder engine. Increasing the compression ratio allowed improvement of the maximum diesel substitution from 55 to 82% (also achieving a significant improvement of the thermal efficiency) with methanol and from 91 to 93% with H2 (but decreasing the thermal efficiency due to higher heat transfer losses).

Study of Efficient and Clean Combustion of Diesel–Natural Gas Engine at Low Loads with Concentration and Temperature Stratified Combustion

The approach for achieving efficient and clean combustion in a diesel–natural gas (NG) heavy-duty engine at low loads was studied by computational fluid dynamics simulation. This study proposed the concentration and temperature-stratified combustion technology and clarified its mechanism. The results revealed that different stratified combustions can be organized by controlling the pressures, timings, and durations of diesel and NG injections, and stratified combustion can be classified into moderate, lean, and rich stratified combustion modes. Efficient and clean combustion can be realized simultaneously at low engine loads: the gross indicated thermal efficiency (ITEg) of engine breakthrough was improved to 47.9%, and the indicated-specific emissions of unburned hydrocarbon (ISUHC) were greatly reduced to 1.6 g/kWh, while the indicated-specific emissions of nitrogen oxide (ISNOx) remained at 0.6 g/kWh. Moreover, the detailed analysis of three typical stratified combustion modes demonstrates that coupling control of the concentration and temperature of the charge is the key to obtaining excellent engine performance. Most of the NG-stratified mixture should burn in the react ratio range of 0.4 to 0.8 for low unburned hydrocarbon emissions, low nitrogen oxides emissions, and rapid combustion. The proper temperature stratification should ensure that a high-temperature charge is around the over-lean NG mixture. This study can provide the fundamentals of stratified combustion control and feasible solutions for commercial applications of NG engines.

A hybrid predictive maintenance approach for ship machinery systems: a case of main engine bearings

A hybrid maintenance strategy is proposed, combining reliability-centered and condition-based maintenance strategies to prevent engine failures. A case study on the lubrication deficiency of a ship's main engine bearings was conducted. The reliability-centered maintenance phase is based on reliability-increasing rules, equipment facts, and a knowledge base. Then, a strategy is developed where system parameters are continuously monitored. These parameters are evaluated in the inference engine, and maintenance recommendations are provided to the ship operator. The investment cost of th developed system is discussed using a real engine failure case. The study shows that the strategy can improve maintenance on existing ships and system reliability at low costs. The methodology offers a cost-effective approach for the sustainability of the main engine, as demonstrated by a real crankshaft failure report. Unlike existing practices, it provides influential maintenance decisions based on evaluating system parameters within four operation ranges. Simulations show it detects insufficient lubrication faults at low engine loads, superior to current applications. The proposed approach suits different types of existing and newly built ships, engines like dual-fuel, and technologies such as semi-autonomous ships.

Butanol and selective catalytic reduction of gaseous emissions in a heavy-duty diesel engine

The impact of renewable fuels and their blends on vehicle exhaust emissions remains of high interest. In this study, we investigate the effect of butanol on the conversion efficiency of a Selective Catalytic Reduction (SCR) system installed on a commercial Euro V heavy-duty diesel engine (HDDE). Exhaust emissions were measured upstream and downstream of the SCR during dynamometer tests using diesel fuel and various butanol-diesel blends (5/95 %v, 10/90 %v, and 20/80 %v). Steady-state tests according to the World Harmonized Stationary Cycle (WHSC) on an engine bench were conducted including measurements of nitrogen oxides (NOX), total hydrocarbons (THC), and carbon monoxide (CO) emissions utilizing a portable emission measurement system (PEMS). The results showed a reduction in exhaust gas temperature (EGT) of around 4 % for a butanol content of 20 %. The use of butanol increased conversion efficiency of the SCR system by 4 % compared to diesel. The maximum SCR system conversion rate of around 96 % was obtained with a butanol content of 10 %. For all fuels, NOX conversion decreased at high engine loads (above 400 °C), while, as expected, was zero at low engine loads (below 200 °C). Reductions in CO and THC emissions were observed downstream of the SCR system. In general, this study shows that an SCR originally designed for a Euro V diesel engine can be equally effective when the engine is running on a partial blend of butanol.

Blends of Salvinia molesta oil microemulsion with diesel in an unmodified diesel engine for the simultaneous reduction of nitrogen oxide and smoke

In this study, microemulsion synthesized from chemically extracted Salvinia molesta oil with diesel was evaluated as fuel in stationary unmodified diesel engine. The microemulsions from S. molesta oil was prepared using the best combinations of 67% S. molesta oil, 15% ethanol, 13% water and 5% surfactant (span 80) and its properties were compared with that of diesel. The engine test conducted with M10, M20 and M30 blends and reported a brake thermal efficiency of 29.76% and brake specific fuel consumption of 0.3239 kg/kWh with M20. The emissions like NO and smoke reduced by 18.07% and 7.37%, respectively, with marginal increase in CO, CO2 and unburned hydrocarbon by 3.8%, 3.4% and 16.66% respectively, with M20 compared to diesel at maximum engine load of 3.73 kW. At lower engine loads with M10, M20 and M30 slightly lower CO2 emission than diesel. A drop in peak pressure and heat release rate was found to be 1.73% and 8.40%, correspondingly with M20, as that of diesel. Even though a slight reduction in brake thermal efficiency observed with M20 as compared to M10 and diesel by considering the lowest emissions of NO and smoke, it is feasible to use as promising fuel for unmodified diesel engines.

An Innovative Retrofit Design for Energy Efficiency and Emission Reduction: MAN B&W Marine Engine Slide Fuel Injector

Background:: The fuel injector is one of the most essential parts in marine diesel engines. For MAN B&W two-stroke engines, the conventional fuel injector, due to the existence of sac volume, can result in problems such as increased emission and fuel consumption and shortened service life of combustion chamber components. Objective:: The MAN B&W marine engine slide-type fuel injector is a structural retrofit of conventional injectors, improving diesel engine combustion conditions, fuel efficiency, and emission reduction in hydrocarbon, NOx, smoke, and particulate matter by eliminating sac volume with patented technology. Methods:: This study employed a comparative analysis approach to evaluate the performance of conventional fuel injectors versus slide-type fuel injectors in MAN B&W two-stroke engines. Data collection involved practical experiences, onboard operations, and analysis of fuel efficiency, emission reduction, and combustion improvement. The structural differences and operational advantages of both injector types were examined to assess the environmental benefits and economic implications of adopting slide fuel injectors. Recommendations for the gradual replacement of conventional injectors with slide-type injectors were based on empirical data and industry best practices. Results:: Slide fuel injectors obtain a reduction of about 75% of the HC emissions at all loads. The slide fuel injector significantly decreases the smoke emission level at low engine load, at 25% load. A reduction in PM of up to 50% has been confirmed, and slide fuel injectors can reduce NOx emission by approximately 15% on average. result: The smoke emission level at low engine load, at 25% load in particular, is greatly decreased by slide fuel injector. Conclusion:: Slide fuel injectors, with a granted patent, are commonly used in marine low-speed engines due to their advantages.

Exploring the passive the pre-chamber ignition concept for spark-ignition engines fueled with natural gas under EGR-diluted conditions

The pre-chamber ignition system has demonstrated to be a suitable technology for increasing burning rates while reducing the cycle-to-cycle variability in spark-ignition engines. This concept offers an improvement in thermal efficiency through an increase in ignition energy and flame surface, allowing it to overcome knocking combustion issues at high engine load/speeds. This fact makes this ignition concept well compatible with the use of dilution strategies to control emissions or to further improve efficiency. However, despite promoting faster combustion, knocking combustion is still a major limitation at low rotational speeds and high engine loads (low-end torque). In this investigation, the performance of the passive pre-chamber concept is evaluated in a single-cylinder turbocharged spark-ignition engine fueled with compressed natural gas in EGR-diluted conditions. Several experiments and numerical simulations are combined to analyze the basis of the pre-chamber operation, while seeking to improve the global performance of the engine. To this end, a new pre-chamber geometry is proposed that is able to achieve better features in the ejected jets, to enhance the performance of the concept in the whole engine map.

Performance and carbon emissions of a diesel/oxy-hydrogen dual-fuel engine with oxy-hydrogen injection variation under low and medium load conditions

Reducing carbon emissions such as carbon dioxide (CO2) and carbon monoxide (CO) from diesel engines struggled with engine performance challenges and fossil fuel limitations. Besides, huge transportation such as ships hardly replaced diesel engines due to the higher thermal efficiency and low operation cost. Oxy-hydrogen gas, as a carbon-free gas, could potentially improve diesel engine performance and carbon emissions. Most of the studies tried to identify the effect of oxy-hydrogen induction into diesel engine combustion on performance and emissions. However, this study evaluated oxy-hydrogen injector sizes to the diesel engine performance and carbon emissions at several loads and several engine speed conditions. Overall, the result showed that the oxy-hydrogen gas injection into the diesel engine’s intake port improved the performance and carbon emissions compared to the single diesel fuel as a baseline. High engine performance with low carbon emissions could be achieved at low and medium engine load conditions with high engine speeds. Moreover, smaller oxy-hydrogen injector sizes were suitable for the medium engine load and vice versa, to improve the performance and carbon emissions. At low load, the engine performance improvement of engine torque, specific fuel consumption, and thermal efficiency were 1800 to 2200 rpm. Moreover, the CO2 and CO emissions reductions were also suitable with 2200 rpm with a bigger oxy-hydrogen gas injector (6 mm). Furthermore, at medium load, the engine performance improved at 1400 rpm but the CO2 and CO emissions were lower at 2200 rpm with a small oxy-hydrogen gas injector (4 mm). The engine operation at 2200 rpm with a 4 mm injector also improved the engine performance regarding carbon emissions reduction. However, injecting oxy-hydrogen gas into diesel engines had the potential to enhance the engine performance and reduce carbon emissions, moving closer to achieving zero emissions

Optimizing CI Engine Ethanol Fuel Induction Techniques Using the AHP-PROMETHEE II Hybrid Decision Model

Ethanol along with nanoparticles stands out as a promising alternative in the pursuit of environmentally sustainable fuel options, offering a potential solution to the dual challenge of curbing NOx and PM/soot emissions while optimizing engine performance in compliance with stringent pollution regulations for compression ignition (CI) engines. The research study aims to optimize ethanol fuel induction techniques for CI engines. It utilizes a hybrid decision-making approach that integrates the analytic hierarchy process- AHP- for problem structuring and the derivation of preference weights. Subsequently, the preference ranking organization method for enrichment evaluations-PROMETHEE II is applied to assess and rank the existing alternatives. The study entails a methodical assessment of diverse ethanol induction methods across varying engine load ranges, considering multiple criteria including engine performance, emissions, combustion behavior, and exhaust after-treatment efficiency. Hybrid AHP-PROMETHEE II model provides criteria weights and ranks ethanol induction techniques and fuel blends across low, medium, and high engine loads for decision-making. It ensures that the method chosen aligns with goals, such as reducing NOx and soot emissions, optimizing engine performance, enhancing combustion, and minimizing exhaust after-treatment costs for CI engines. According to the research findings, the hybrid AHP-PROMETHEE II model identifies the CI engine operating at medium load with ethanol blending (DE10) and without the use of nanoparticles as the preferred choice. Additionally, AHP-PROMETHEE II (AHP derived criteria weights) and PROMETHEE II (direct rating derived criteria weights) models, suggested DE10 with nanoparticle (DE10_NP) using blending technique at low load and combined blending-fumigation technique with nanoparticles at high load. However, at medium load, PROMETHEE II recommends DE10_NP, while AHP-PROMETHEE II recommends DE10 blending technique. To assess the performance and reliability of this model, the consistency ratio and Spearman's rank correlation coefficient indices were computed, yielding values of 0.05 and 0.59, respectively. Both indices fall below the predetermined threshold limits, indicating a high level of consistency of the model.

Evaluation of ammonia-gasoline co-combustion in a modern spark ignition research engine

Ammonia (NH3) is emerging as a potential favoured fuel for longer range decarbonised heavy transport, particularly in the marine sector, predominantly due to highly favourable characteristics as an effective hydrogen carrier. This is despite generally unfavourable combustion and toxicity attributes, restricting end use to applications where robust health and safety protocols can always be upheld. In the currently reported work, a spark ignited thermodynamic single cylinder research engine equipped with gasoline direct injection was upgraded to include gaseous ammonia port injection fuelling, with the aim of understanding maximum viable ammonia substitution ratios across the speed-load operating map. The work was conducted at varied effective compression ratios under overall stoichiometric conditions, with the spark timing re-optimised for maximum brake torque at all stable logged sites. The experiments included industry standard measurements of combustion, performance, and engine-out emissions (including NH3 “slip”). With a geometric compression ratio of 11.2:1, it was found possible to run the engine on pure ammonia at low engine speeds (1000-1800 rpm) and loads of 12 bar net IMEP. When progressively dropping down below this load limit an increasing amount of gasoline co-firing was required to avoid engine misfire. When operating at 1800 rpm and 12 bar net IMEP, all emissions of carbon (CO2, CO, unburned hydrocarbons) and NOx decreased considerably when switching to higher NH3 substitution ratios, with NOx reduced by ~ 45% at 1800 rpm/12 bar when switching from pure gasoline to pure NH3 (associated with longer and cooler combustion). By further increasing the geometric compression ratio to 12.4 and reducing the intake camshaft duration for maximum effective compression ratio, it was possible to operate the engine on pure ammonia at much lower loads in a fully warmed up state (e.g., linear low load limit line from 1000 rpm/6 bar net IMEP to 1800 rpm/9 bar net IMEP). Under all conditions, the indicated thermal efficiency of the engine was either equivalent to or slightly higher than that obtained using gasoline-only due to the favourable anti-knock rating of NH3. Ongoing work is concerned with detailed breakdown of individual NOx species together with measuring the impact of hydrogen enrichment across the operating map.

Impact of thermal swing piston top land coatings on gasoline engine performance and raw emissions

Upcoming legislations aim to significantly reduce carbon dioxide and hydrocarbon emissions compared to current regulations. Accordingly, options have to be evaluated to not only convert the raw emissions in a catalytic converter, but also to reduce the raw emissions from the combustion process in the first place. Therefore, thermal piston top land coatings, which lead to an oscillating piston surface temperature were investigated on a single cylinder research engine using a gasoline RON95E10 fuel. Measurements were conducted at a compression ratio of 12.2 and a long Miller intake event. In this manuscript the results achieved with yttria stabilized zirconia in comparison to an uncoated piston are displayed. Significant effects of the coatings on the indicated efficiency could be observed mainly at low engine speeds and loads due to the high share of fuel energy in the wall heat losses and incomplete combustion. At these operating points, the reduction of wall heat losses can almost be fully transferred into indicated efficiency, leading to an increase in indicated efficiency of 6.3% by the yttria stabilized zirconia coating. At higher engine speeds and loads, the advantage in indicated efficiency vanishes and a decrease of 0.5% can be observed. Near full load operation the indicated efficiency slightly lower. However, the effects of a thermal swing coating on combustion efficiency and wall heat losses strongly depend on the operation conditions.

Experimental study on combustion, performance, and emission characteristics of a homogeneous charge compression ignition engine fuelled with multiple biofuel-gasoline blends

For sustainable future mobility and power generation applications, there is a compelling need to develop flex-fuel engines that operate with multiple regional or season-specific biofuels. The present investigation focussed on mitigating agricultural diesel engines’ pollutant emission and performance problems. A systematic experimental study is carried out in a modified agricultural diesel engine to compare and evaluate the engine characteristics of the biofuel-gasoline blends fuelled Homogeneous Charge Compression Ignition (HCCI) mode. Seven different oxygenated biofuels: acetone, ethanol, methanol, isopropanol, isobutanol, ethyl acetate, and diisopropyl ether blended in gasoline, were investigated. 2-Ethylhexyl nitrate was used to improve the reactivity of fuel blends to the extent that lower engine loads could be reached. All the investigated biofuel-gasoline blends could produce permissible emission levels by suitably tuning the fuel proportions. The total nitrogen oxides and smoke emissions were below 2.8 and 0.0007 g/kWh, respectively, for all the investigated biofuel-gasoline blends at all the HCCI engine load conditions. The highest indicated thermal efficiency of 42% was attained using 60% ethanol/34% gasoline/6% 2-EHN blend in the HCCI engine at 4.63 bar BMEP (86% rated load), a notable 25% improvement compared to the conventional diesel engine. A detailed investigation was done to elucidate the HCCI engine performance (indicated thermal efficiency) trend variations with biofuel type and engine load. The Response Surface Method was adopted to correlate the maximum and the minimum engine load with the fuel composition and properties. The Desirability Approach provided the optimum fuel composition and properties to maximize the engine load range. The optimum solution achieved the engine load range of 20%–89% rated load. Overall, a compact, efficient, and clean HCCI combustion-based engine technology was developed that could be operated using multiple biofuels over an expanded load range.

Comparative evaluation of different operating parameters on performance, combustion, and emission characteristics in gasoline compression ignition (GCI) engine by using carbon neutrally biofuels

The stringent emission regulations and energy shortage put forward strict requirements for highly efficient and clean combustion for internal combustion engines. The gasoline compression ignition (GCI), which is a new advanced combustion concept, can obtain high efficiency and low emissions simultaneously without many modifications of standard diesel engines. However, little research has been carried out to synergistically optimize the operation parameters in a wide load range, especially fueled with the carbon neutrally biofuels. Therefore, in this paper, the effects of various operating parameters on engine performance, combustion, and emission characteristics of the gasoline compression ignition (GCI) strategy fueled with a blend of butanol and biodiesel were investigated. Specifically, the impact of butanol energy ratio, fuel direct injection timing, and exhaust gas recirculation (EGR) at the indicated mean effective pressure (IMEP) of 4, 8, and 14 bar and the butanol energy ratio of 60%, 70%, and 80% were examined. Result shown that the increase in butanol energy ratio decreased the fuel reactivity and worsen the combustion process, while the lower butanol energy was also disadvantage to the engine performance. The indicated thermal efficiency could achieve 48.5% when the butanol energy ratio was 70% at medium engine load. The earlier fuel injection timing was needed at low engine load, the EGR was necessary to inhibit the in-cylinder pressure rise at high engine load, in which the EGR rates of 20% at the IMEP of 8 bar and 30% at the IMEP of 14 bar could achieve the optimum engine performance, respectively. Meanwhile, the nitrogen oxides emissions shown a greatly decrease with the EGR rates increase, and it was less than 200 ppm at the IMEP of 14 bar when the EGR rates were 50%.

Effects of pre-chamber flow-field on combustion stability in a spark-ignition engine using large-eddy simulations

Significant efforts are under way to develop innovative ignition systems for spark-ignition engines used in transportation. Within this context, passive pre-chamber technology has emerged as a promising alternative for passenger cars. However, several uncertainties remain regarding the operation of this concept at low engine loads and speeds, as well as the impact of specific design features on combustion stability. Previous investigations have indicated that the tangential angle of the pre-chamber holes can play a vital role in stabilizing the combustion process. Nonetheless, the underlying thermo-physical phenomena responsible for these results have not yet been thoroughly studied. To address these knowledge gaps, this paper presents a numerical study using a computational fluid dynamics model that has been validated with experimental results. An alternative modeling methodology was developed to conduct multi-cycle large-eddy simulations and investigate two different pre-chamber configurations, one with tangential holes and the other with radial holes. The results revealed an intriguing correlation between the combustion stability and the spatial distribution of the flame inside the pre-chamber. The cycle-to-cycle dispersion of pre-chamber flow variables was significantly higher when using radial holes compared to tangential holes, potentially explaining the unstable behavior of the former design. Additionally, the undesirable flow-field of the radial-hole pre-chamber caused the flame to evolve asymmetrically, resulting in substantial variations in the ejected jets. This asymmetry can significantly affect the morphology of the main chamber ignition in each cycle.

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).

A Comparison of Hydrogen and Gasoline Piston Ring Simulations

This paper presents a transient mixed-lubrication hydrodynamic and gas flow simulation model for a piston ring pack for a four-stroke internal combustion engine. The analyses carried out compare two fuel types, hydrogen and gasoline, at a 2000 rpm low engine load (20%), as well as 3000 rpm low (20%) and high (100%) engine loads, to investigate the effects of the different fuels and loading conditions on the ring pack. In particular, the minimum oil film thickness at the top compression ring, the total ring friction of the ring pack, the friction power loss and the blow-by are studied. The simulation shows that, under the high load conditions at 3000 rpm, the hydrogen variant exhibits larger friction power losses, around a 200 W peak difference and larger blow-by throughout the expansion stroke of the engine cycle. A similar trend can be observed for the low loads, where larger friction power losses with peak differences of 30 W and 40 W for 2000 rpm and 3000 rpm, respectively, are observed. The blow-by results for the low load at 2000 rpm show a slight increase of approximately 22% more gas flow into the crankcase, while the 3000 rpm simulation shows a 50% increase in blow-by for the hydrogen variant at low load and a 40% increase at high load. The findings that are presented indicate that, although alternative fuel sources such as hydrogen are very attractive alternatives to fossil fuels such as gasoline, there can be unwanted side effects that could lead to the permanent damage of components through quicker wear or hydrogen embrittlement from the blow-by gas.

The effect of intake port shape on in-cylinder flow field and turbulence distribution in a high-tumble production engine with endoscope accesses

Three cylinder heads with varied intake port shapes are experimentally investigated to evaluate intake flow structures and their influence on near top dead centre (TDC) flow fields and turbulence distributions in a motored high-tumble engine. The endoscopic high-speed particle image velocimetry (eHS-PIV) is implemented in multi-cylinder engines with two laser endoscopes and a camera endoscope installed in the cylinder head. For a range of engine load and speed conditions, particle seeded and laser illuminated high-speed movies are recorded for 100 cycles with which ensemble-averaged flow fields and spatial-filtered high-frequency flow magnitude distributions are analysed. The results show that a straighter intake port producing a more lateral flow direction results in a larger swinging arc, which is related to enhanced flow later in the compression stroke. The tumble vortex shows an asymmetric structure; the flow field during the compression stroke exhibits higher magnitude vectors at the leading head. This surging flow head becomes stronger with a straighter intake port, which leads to enhanced tumble vortex formation near TDC. As it becomes very strong, the flow vectors originally directed towards the exhaust valves bounce back towards the intake valves, causing a very complex flow structure involving multiple flow components. The result is enhanced turbulence throughout the late compression stroke including the spark timing. However, the impact of the straighter intake port shape on TDC turbulence becomes less significant at lower engine load and speed conditions as the lower intake air momentum limits the enhancement.

Multi-injection investigation of a high-volatility diesel in advanced compression ignition combustion for NOx control

Traditional selective catalytic reduction aftertreatment technologies used to reduce [Formula: see text] are very limited at exhaust temperatures below [Formula: see text]. Therefore, under these low engine load conditions, having effective in-cylinder control of [Formula: see text] emissions is important. Previous work by the authors explored the effect of fuel physical properties on the ability to control [Formula: see text] in-cylinder. That work was limited to one direct injection near top dead center. Modern diesel high-pressure fuel systems have the capability of five or more injections in one engine cycle. A higher-volatility diesel fuel and high amounts of exhaust gas recirculation to delay ignition could provide an opportunity for reduction in engine-out [Formula: see text] through an increased level of fuel premixing. By appropriately timing multiple short injections, a more optimal distribution of fuel in-cylinder may be achieved, which could reduce [Formula: see text] while maintaining an efficient combustion phasing. A computational fluid dynamics model previously validated against experimental data was used to explore several injection strategies with increased levels of fuel premixing to assess the potential trade-offs between [Formula: see text] and CO/unburned hydrocarbon (UHC) emissions and thus reduce reliance on the aftertreatment system for [Formula: see text] control. The results show that the devised injection strategies resulted in an increased level of fuel premixing. However, none of the attempted injection strategies resulted in significant [Formula: see text] reductions, and all strategies showed a significant increase in CO and UHC emissions.

Research on active modulation of gas turbine cooling air flow

Gas turbines are the core power equipment for efficient energy conversion and clean utilization. Their hot components operate in environments that largely exceed the heat resistance limit of materials, using cooling air to maintain operation, but the cooling air is often in excess at low engine loads. Therefore, this paper proposes the active modulation of turbine cooling air flow to improve their cycle efficiency by appropriately reducing the cooling air flow rate at low engine loads. Accordingly, a dynamic gas turbine model applicable for the active modulation of turbine cooling air flow is established, along with an analytical turbine vane cooling model considering air-film cooling and thermal barrier coating. For the first time, this paper distinguishes between the hot gas parameters on the pressure and suction surfaces of turbine blades. Additionally, a new concept of equivalent air-film coverage is proposed and optimized by genetic algorithms to make the model calculation results closer to actual temperature distribution. A cooling air active modulation system combining open-loop and closed-loop control is the first ever designed. Studies indicate that active coolant modulation can significantly improve gas turbine efficiency at partial loads. Finally, the possibility of active coolant modulation to suppress blade overheating and enhance blade’s service life under off-design conditions is analyzed.