Light-duty Compression Ignition Engine Research Articles

Technical evaluation of low-carbon fuels as a decarbonization pathway of the light-duty transport sector

The need to rapidly reduce greenhouse gas emissions from the transportation sector has renewed interest in low-carbon fuels, both from the production and utilization standpoint. The maturing of alternative processes to synthesize fuels from atmospheric CO2 and renewable non-edible feedstocks constitutes an interesting proposition, which needs to be matched by favorable drop-in properties and environmental performance once applied to internal combustion engines. To this end, the authors investigate the use of diesel-like high-reactivity and low-reactivity LCFs in a light-duty compression-ignition engine by experimentally assessing their implementation with existing hardware (drop-in) and discussing possible modifications to achieve improved results through calibration. The results revealed that high-reactivity fuels could operate under similar conditions to the standard diesel fuel, exhibiting similar efficiency and soot emissions combined with important reductions in NOx emissions. On the other hand, low-reactivity LCFs show advantages in promoting alternative combustion concepts because of the longer ignition delays, which make it possible to use lower injection pressures and have more stratified air–fuel mixtures, but at the same time, the results revealed that the implementation of these fuels might suffer from hardware limitations which worsens the combustion stability and the operation at low-load. Although the fuels tested exhibited variations in Tank-to-Wheel due to their carbon content and fuel economy, it was found that Well-to-Wheel CO2 intensity is eventually dominated by the renewable content of the fuel and the CO2 is greatly impacted by its production pathway, rather than the fuel consumption optimization. Finally, the study confirmed that, for the successful adoption of oxygenated low-carbon fuels (including alcohols), appropriate material selection in the engine fuel system and fuel additives are necessary to prevent components and seal performance degradation.

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).

Detailed assessment of exhaust emissions in a diesel engine running with low-carbon fuels via FTIR spectroscopy

Low-carbon fuels have been proposed as alternatives that can help with the transition to a sustainable and decarbonized transport sector. This study examines the potential of four different fuel blends with different renewable content to reduce pollutant emissions by evaluating both regulated and unregulated emissions produced by their combustion in a light-duty compression ignition engine. The study distinguishes between two measurement conditions: drop-in and optimized calibration. The drop-in calibration represents the operation of low-carbon fuels using baseline injection settings, while the optimized calibration involves a specific approach to reduce nitrogen oxide emissions. Unregulated emissions were measured using a Fourier Transform Infrared analyzer, which recorded various substances, including aldehydes (acetaldehyde, formaldehyde), saturated hydrocarbons (ethylene, propylene, 1,3 butadiene, and isobutylene), unsaturated hydrocarbons (methane and ethane), aromatics (benzene and toluene), and the greenhouse gas nitrous oxide (N2O). Results indicated that aldehyde production is not affected at low-load operation for fuels with higher oxygen content, but instead, the use of diesel from vegetable origin in the fuel blend could lead to slight increases in this species. On the other hand, the production of saturated hydrocarbons was impacted by the cylinder temperature and combustion duration, being the oxygenated fuels with longer combustion durations at low-load, which reported reductions, but at mid-load, this effect is mitigated. In addition, the production of aromatics and unsaturated hydrocarbon emissions were assessed as soot precursors. The production rate of these species was higher when the calibration was applied due to the reductions in NOx and increases in soot emissions. Lastly, the results of N2O emissions showed slight decreases in the combustion of oxygenated fuels when using the drop-in calibration, but these emissions returned to similar diesel levels when applying the optimized calibration. Overall, the results of the investigation show the potential of these LCFs to meet the regulations but also not sacrificing the emissions performance of unregulated species.

Parametric evaluation of neat methanol combustion in a light-duty compression ignition engine

Methanol is currently considered a promising alternative fuel for energy de-fossilization due to its simplicity and adequacy for renewable production. This study investigates the feasibility of using neat methanol in high-efficiency compression ignition engines, with a focus on its potential to reduce CO2 emissions compared to conventional diesel. However, achieving efficient combustion of neat methanol in compression ignition engines presents challenges due to its low ignition capability, requiring higher compression ratios, intake temperatures, and pressures than diesel for autoignition. Furthermore, the high latent heat of vaporization contributes to significant cycle-to-cycle combustion variability. This work evaluates the combustion characteristics of neat methanol in a light-duty multi-cylinder compression ignition engine with a 19:1 compression ratio, examining its suitability for commercial applications. Performance indicators such as engine efficiency, fuel consumption, and engine-out pollutant emissions are assessed. The findings contribute to advancing research and implementation of methanol fuel as an energy source for internal combustion engine vehicles, addressing both the advantages of the fuel and the challenges that need to be overcome, particularly with respect to its low auto-ignition characteristics. Notably, despite methanol's lower energy density compared to diesel, the achieved combustion efficiency is comparable, with remarkable improvements in NOx and soot emissions trade-off.The study reveals that neat methanol combustion poses difficulties, especially at low loads, speeds, and during engine startup, due to its high ignition energy requirement and long ignition delay. Even with modifications such as increased compression ratio, and the addition of intake heaters and glow plugs, sustaining combustion at low load conditions remains a challenge. However, once the engine is warmed up, methanol combustion can be sustained at medium to high loads without additional heating accessories, although the use of such accessories improves combustion stability.

Evaluation of the Effect of Low-Carbon Fuel Blends’ Properties in a Light-Duty CI Engine

<div class="section abstract"><div class="htmlview paragraph">De-fossilization is an increasingly important trend in the energy sector. In the transport sector the de-fossilization efforts have been centered in promoting the electrification of vehicles, nonetheless other pathways, like the use of carbon neutral or carbon-offsetting fuels under current vehicle fleets, are also worth considering. Low-carbon fuels (LCF) can be synthetized from sources that can take advantage of the carbon already present in the atmosphere (either by technologies like direct carbon capture or biological processes like photosynthesis in biofuels) and use energy from renewable sources for the necessary industrial processes. Although, LCFs can be compared to fossil fuels as energy sources for internal combustion engines, their composition is not the same and their properties can modify the engine combustion and emissions. This work evaluates the use of several diesel-like LCFs in a light duty compression ignition engine and correlates the fuel consumption, NOx, soot and CO<sub>2</sub> emissions to the fuel properties. Results indicate that the combined effect of a low density, low aromatic proportion, high energy density and high cetane number Fischer-Tropsch/FAME fuel blend can maintain the fuel consumption and soot emissions close to results with diesel at most engine conditions and reduce NOx emissions 0.5 - 2.5g/kWh. It was also observed that fuels with higher proportions of OMEx (with lower energy density and increased oxygen proportion) can reduce the soot emissions for the same level of NOx emissions with a fuel consumption penalty. Tank-to-wheel CO<sub>2</sub> emissions show little variation between fuels, while the well-to-wheel emissions are proportional to the renewable content.</div></div>

Development and experimental testing of an integrated prototype based on Stirling, ORC and a latent thermal energy storage system for waste heat recovery in naval application

This paper focuses on an advanced energy system, able to increase the overall efficiency of ships by recovering the heat wasted by the propulsion system. A small-scale prototype has been realized, developed, and tested under realistic operating conditions of boat during a winter and summer cruise. The main novelty of the research that has been presented in this paper lies in a significant contribution by developing an integrated dynamic device for electrical production and thermal energy storage. It is based on a 1000 cm3 light duty compression ignition engine coupled with a properly adapted Stirling Engine (SE), an Organic Rankine Cycle group (ORC) and a latent Thermal Energy Storage system (TES). All the components have been managed by means of a specifically developed electronic control, simulating two standard cruise profiles. Scaled engine power data have been imposed to simulate port, manoeuvring and open sea navigation phases. The consumption of hot water has been obtained by considering the typical hourly use profile of a cruise ship.It has been demonstrated that the proposed integrated system allows recovering all the thermal energy needed to satisfy the hot water request during the cruise, avoiding the use of auxiliary boilers. The results indicate a favourable effect because the recovered thermal energy represents the 7.7 % of the total energy consumed by fuel. The net electrical energy generated by ORC and Stirling engine resulted to be about 1 % of the total fuel energy consumption, respectively 0.8 % and 0.2 %. The developed prototype can be a useful tool in viability analysis and can easily be reproduced for several uses. In conclusion, the integration of different systems with an optimal integration and sizing of the thermal energy storage considerably improve the thermodynamic, economic and environmental results for future clean ships.

Parametric assessment of the effect of oxygenated low carbon fuels in a light-duty compression ignition engine

Low carbon fuels (LCF) are proposed as an alternative to help in the reduction of CO2 emissions from the energy sector, specially related to transportation. These fuels, due to their synthesis process, can generate carbon offsets that mitigate the combustion emissions, while at the same time they can have other properties that reduce criteria pollutants like soot. The current study evaluates the combustion characteristics, performance, and emissions of three LCFs with 100%, 66% and 33% renewable content in volume. The fuels are assessed as drop-in alternatives for diesel, using a baseline calibration present in commercially available vehicles, and with an optimized calibration that targets NOx emissions reductions. The optimized calibration is reached by performing a design of experiments (DOE) that allows to create linear models to observe the engine response based on injection and air management settings for each of the LCFs at three operating conditions. Then the cases with similar combustion phasing are evaluated to determine the settings that can provide the lowest NOx and soot emissions without worsening fuel consumption and engine efficiency. It is found that when the LCFs are used as drop-in alternatives soot emissions are reduced when compared to diesel while brake-specific fuel consumption (BSFC) is increased by nearly 10 g/kWh. In contrast, the optimized calibration achieves average NOx reductions of 44% when compared to diesel. Under both calibrations well-to-wheel CO2 reductions of nearly 96% are achieved when the fuel with highest renewable proportion is used.

Effect of Intake Air Temperature and Premixed Ratio on Combustion and Exhaust Emissions in a Partial HCCI-DI Diesel Engine

Homogeneous charge compression ignition (HCCI) is considered an advanced combustion method for internal combustion engines that offers simultaneous reductions in oxides of nitrogen (NOx) emissions and increased fuel efficiency. The present study examines the influence of intake air temperature (IAT) and premixed diesel fuel on fuel self-ignition characteristics in a light-duty compression ignition engine. Partial HCCI was achieved by port injection of the diesel fuel through air-assisted injection while sustaining direct diesel fuel injection into the cylinder for initiating combustion. The self-ignition of diesel fuel under such a set-up was studied with variations in premixed ratios (0–0.60) and inlet temperatures (40–100 °C) under a constant 1600 rpm engine speed with 20 Nm load. Variations in performance, emissions and combustion characteristics with premixed fuel and inlet air heating were analysed in comparison with those recorded without. Heat release rate profiles determined from recorded in-cylinder pressure depicted evident multiple-stage ignitions (up to three-stage ignition in several cases) in this study. Compared with the premixed ratio, the inlet air temperature had a greater effect on low-temperature reaction and HCCI combustion timing. Nonetheless, an increase in the premixed ratio was found to be influential in reducing nitric oxides emissions.

Performance and emissions of renewable blends with OME3-5 and HVO in heavy duty and light duty compression ignition engines

Interest in poly(oxymethylene)dimethyl ether (OME3-5) as an alternative to fossil fuels in compression ignition engines has increased owing to its potential for soot reduction. The high oxygen content of the polymer and lack of carbon–carbon bonds and aromatic structures can help to reduce engine out soot emissions. However, OME3-5 is potentially damaging to engine components, and thus engine modifications are required when using neat OME3-5.In the present study, OME3-5 was blended with hydrotreated vegetable oil (HVO), rapeseed methyl ester and the C8-alcohol 2-ethylhexanol (an isomer of n-octanol) to ensure miscibility. Three blends were designed with an oxygen content of 6.4, 12.8 and 17.8% by mass. Performance and emissions were compared to the reference fuels fossil diesel and HVO in a single cylinder light duty and heavy duty compression ignition engine at different loads.Evaluation of the combustion in both engines showed similar trends: The indicated thermal efficiency was slightly higher for the oxygenated fuel and the combustion duration shorter compared to diesel. Due to the lower heating value of the blends, the indicated specific fuel combustion increased with increasing share of OME3-5 in the blend.For both engines, engine out soot emissions were decreased strongly, whereas NOx emissions were slightly increased. Analysis of the particle size distribution showed a decrease in the particle number of agglomerated particles (>30 nm) for the blends. For the heavy duty engine, an increase in nucleation mode particles (<30 nm) was measured.

A comparative study on the performance of partially premixed combustion (PPC), reactivity-controlled compression ignition (RCCI), and RCCI with reverse reactivity stratification (R-RCCI) fueled with gasoline and polyoxymethylene dimethyl ethers (PODEn)

To solve the challenges of the high heat release rate of partially premixed combustion (PPC) and low combustion efficiency of reactivity-controlled compression ignition (RCCI), RCCI with reverse reactivity stratification (R-RCCI) fueled with gasoline and polyoxymethylene dimethyl ethers (PODEn) was investigated at low and medium loads in a light-duty compression-ignition engine in this study. The results indicated that R-RCCI has moderate combustion rate and combustion efficiency between PPC and RCCI. At both low and medium loads, R-RCCI has the highest indicated thermal efficiency (ITE) due to its relatively lower heat transfer losses compared with PPC. Moreover, the nitrogen oxides (NOx) and soot emissions of R-RCCI are significantly lower than that of PPC. Although RCCI has the lowest heat transfer losses, its considerably low combustion rate leads to substantial exhaust losses and thereby yields a low ITE. Compared with RCCI, R-RCCI has a better balance between the degree of premixed combustion and combustion temperature, which is crucial for soot oxidation, so it has very low soot emissions at both low and medium loads.

Effect of a novel piston geometry on the combustion process of a light-duty compression ignition engine: An optical analysis

The development of new piston geometries has shown great potential to achieve the low levels of soot emissions required by regulation. Thus, the present paper aims to characterize the influence of a new piston design over combustion process. It is characterized by the introduction of protrusions around the periphery of the bowl, evenly spaced. The performance of this geometry is compared to other geometries that have been extensively analyzed in literature, under similar operating conditions. To achieve this objective, a single cylinder optical compression ignition engine was used with full-quartz pistons representing three bowl geometries: re-entrant, stepped lip and wave-stepped lip. Two optical techniques (OH∗ chemiluminescence and Natural Luminosity-NL) were applied for identifying the near-stoichiometric zones and the differences in the combustion evolution. The flame movement was analyzed by applying the combustion image velocimetry (CIV) algorithms. In addition, an in-cylinder pressure analysis was performed for each piston at 4.5 bar and 7.5 bar IMEP and the differences in terms of Rate of Heat Release were highlighted. A more intense reverse flow was clearly identified when using wave protrusions inside the bowl. The stepped lip and wave-stepped lip bowl present faster late cycle oxidation with much near-stoichiometric zones than re-entrant piston.

Experimental Assessment on Exploiting Low Carbon Ethanol Fuel in a Light-Duty Dual-Fuel Compression Ignition Engine

Compression ignition (CI) engines are widely used in modern society, but they are also recognized as a significative source of harmful and human hazard emissions such as particulate matter (PM) and nitrogen oxides (NOx). Moreover, the combustion of fossil fuels is related to the growing amount of greenhouse gas (GHG) emissions, such as carbon dioxide (CO2). Stringent emission regulatory programs, the transition to cleaner and more advanced powertrains and the use of lower carbon fuels are driving forces for the improvement of diesel engines in terms of overall efficiency and engine-out emissions. Ethanol, a light alcohol and lower carbon fuel, is a promising alternative fuel applicable in the dual-fuel (DF) combustion mode to mitigate CO2 and also engine-out PM emissions. In this context, this work aims to assess the maximum fuel substitution ratio (FSR) and the impact on CO2 and PM emissions of different nozzle holes number injectors, 7 and 9, in the DF operating mode. The analysis was conducted within engine working constraints and considered the influence on maximum FSR of calibration parameters, such as combustion phasing, rail pressure, injection pattern and exhaust gas recirculation (EGR). The experimental tests were carried out on a single-cylinder light-duty CI engine with ethanol introduced via port fuel injection (PFI) and direct injection of diesel in two operating points, 1500 and 2000 rpm and at 5 and 8 bar of brake mean effective pressure (BMEP), respectively. Noise and the coefficient of variation in indicated mean effective pressure (COVIMEP) limits have been chosen as practical constraints. In particular, the experimental analysis assesses for each parameter or their combination the highest ethanol fraction that can be injected. To discriminate the effect on ethanol fraction and the combustion process of each parameter, a one-at-a-time-factor approach was used. The results show that, in both operating points, the EGR reduces the maximum ethanol fraction injectable; nevertheless, the ethanol addition leads to outstanding improvement in terms of engine-out PM. The adoption of a 9 hole diesel injector, for lower load, allows reaching a higher fraction of ethanol in all test conditions with an improvement in combustion noise, on average 3 dBA, while near-zero PM emissions and a reduction can be noticed, on the average of 1 g/kWh, and CO2 compared with the fewer nozzle holes case. Increasing the load insensitivity to different holes number was observed.

Characterizing the gaseous and particulate SVOC emissions of a commercial light-duty compression ignition engine via GCxGC-ToF-MS

Semi-volatile organic compounds (SVOCs) in gaseous and particulate states from a commercial light-duty compression ignition (CI) engine burning diesel fuel have been investigated by adopting two dimensional Gas-Chromatography Time-of-Flight Mass-Spectrometry (GC × GC-ToF-MS) coupled with a thermal desorption technique. Owing to the enhanced separation capability of the multidimensional gas chromatography, the SVOCs including 21n-alkanes (C12-C32), 16n-alkylcyclohexanes (C11-C25 and C33) and 13 polycyclic aromatic hydrocarbons (PAHs) (2–5 rings) have been identified and quantified under different steady engine loads. The experimental results demonstrated that at high engine load (8 bar BMEP @ 1800 rpm), SVOC emissions were higher than those at low engine load (2 bar BMEP @ 1800 rpm) by factors of 2.74 and 2.02 for gaseous and particulate states respectively. The impact of the diesel oxidation catalyst (DOC) on engine-out SVOCs was also analyzed. The results demonstrated that SVOCs did not reduce significantly (less than 16% for different compounds) at low engine load but decrease more dramatically at high engine load (by 37%–55%) when the DOC was above its light-off temperature. At high engine load, it turned out to be that the DOC mitigating effect was more remarkably on the gaseous SVOCs (38%–62%) than on the particulate SVOCs (26%–46%). Limited SVOC reductive capability of the DOC spurs the need of catalyst improvement, especially for capturing high molecular weight (HMW) organic compounds. Therefore, it would be desirable to further investigate the relationship between SVOC emissions and different types of aftertreatment techniques (i.e. DPF) in a more specific way.

The classification of gasoline/diesel dual-fuel combustion based on the heat release rate shapes and its application in a light-duty single-cylinder engine

In this research, there are two major sections for analysis: the characteristics of gasoline and diesel dual-fuel combustion and their application to operating load extension with high thermal efficiency and low emissions. All the experiments were completed using a single-cylinder compression ignition engine with 395 cc displacement. In the first section, the dual-fuel combustion modes were classified into three cases by their heat release rate shapes. Staying at 1500 r/min with a total value of 580 J of low heat for each cycle condition, the diesel injection timing was varied from before top dead center with a 6–46 °crank angle with 70% of gasoline fraction based on the low heating value. Among the modes were two suitable dual-fuel combustion modes for a premixed compression ignition. The first suitable mode shows multiple peaks in the heat release rate (mode 2) and the second suitable mode shows a single peak with a “bell-shaped” heat release rate (mode 3). These two dual-fuel combustion types showed a high gross indicated thermal efficiency of up to 46%. Based on the results in the first section, the practical application of dual-fuel premixed compression ignition combustion was investigated considering a high thermal efficiency and a high-load condition. At a 1500 r/min/gross indicated mean effective pressure of 6.5 bar, 48% of the gross indicated thermal efficiency was obtained by using dual-fuel premixed compression ignition combustion mode 3. This mode was typical of a “reactivity controlled compression ignition,” while the nitrogen oxides and the particulate matter emissions satisfied the EURO-6 regulation (0.21 g/kW h and 2.8 mg/m3, respectively). In addition, a high thermal efficiency (45%) with low maximum pressure rise rate, NOx (nitrogen oxides), and particulate matter emissions was obtained at 2000 r/min/gross indicated mean effective pressure 14 bar condition by the adjustment of dual-fuel premixed compression ignition combustion mode 2. As a result, this research contributes to the understanding and practical application of dual-fuel combustion for a light-duty compression ignition engine.

Performance and emissions of diesel-biodiesel-ethanol blends in a light duty compression ignition engine

An approach to reduce CO2 emissions while simultaneously keeping the soot emissions down from compression ignition (CI) engines is to blend in short chained oxygenates into the fuel. In this work, two oxygenated fuel blends consisting of diesel, biodiesel and EtOH in the ratio of 68:17:15 and 58:14:30 has been utilized and studied in a single cylinder light duty (LD) CI engine in terms of efficiency and emissions. The reasons of utilizing biodiesel in the fuel blend is due to the emulsifying properties it has while the origin of the fuel is biomass. When performing the experiments, the control parameters were set as close as possible to the original equipment manufacturer (OEM) EU5 calibration of the multi-cylinder engine to study the possibility of using such blends in close to stock LD CI engines. The oxygenates, in particular the fuel with the higher concentration of EtOH, showed an net indicated efficiency of ∼52% at high load in comparison to diesel which never exceeded ∼48%. Regarding the emissions, several trends were observed; the soot-NOX trade-off diminished significantly when utilizing the fuel with the highest concentration of EtOH. The charge cooling effect reduces the NOX emissions while the exhaust particles are reduced both in terms of mean diameter and quantity. At lower loads, the THC and CO emissions were higher for the oxygenated blends than for the diesel due to the earlier mentioned charge cooling negatively affecting the combustion process. However, this trend seized at the higher loads when the in-cylinder temperature is higher and oxidation of the fuel is enhanced.

Performance and emissions of diesel-gasoline-ethanol blends in a light duty compression ignition engine

An approach to reduce CO2 emissions while simultaneously keeping the soot emissions down from compression ignition (CI) engines is to blend in short chained oxygenates into the fuel. In this work, two oxygenated fuel blends consisting of diesel, gasoline and ethanol (EtOH) in the ratio of 68:17:15 and 58:14:30 have been utilized and studied in a single cylinder light duty (LD) CI engine in terms of efficiency and emissions. The reasons of utilizing gasoline in the fuel blend is due to the emulsifying properties it has while increasing the total octane rating of the fuel to be able to run the engine with a higher fraction of premixed flame. When performing the experiments, the control parameters were set as close as possible to the original equipment manufacturer (OEM) EU5 calibration of the multi-cylinder engine to study the possibility of using such blends in close to stock LD CI engines. With the oxygenates, in particular the fuel with the higher concentration of EtOH achieved an indicated net efficiency of ∼51% inf comparison to ∼47% for diesel at 8 bar BMEP. The NOX emissions increased slightly for the double injection strategy at 13 bar BMEP from ∼13.5 g/kW h to ∼14.5 g/kW h when going from diesel fuel to the higher ethanol blend. However utilizing single injection strategy at lower loads reduces the NOX. Highest soot mass measured for diesel was ∼0.46 g/kW h in contrast to ∼0.1 g/kW h for the oxygenates. Also, soot production when running the engine on the ethanol containing fuels was not significantly affected by EGR utilization as in the case of diesel. Considering particle size distribution, the particles are reduced both in terms of mean diameter and quantity. At 1500 rpm and 2 bar BMEP an increase of over ∼300% in THC and CO was measured, however, increasing the speed and load to above 2000 rpm and 8 bar BMEP respectively, made the difference negligible due to high in-cylinder temperatures contributing to better fuel oxidation. Despite having lower cetane numbers, higher combustion stability was observed for the oxygenates fuels.

Influence of spatial and temporal distribution of Turbulent Kinetic Energy on heat transfer coefficient in a light duty CI engine operating with Partially Premixed Combustion

Emission regulations together with the need of more fuel-efficient engines have driven the development of promising combustion concepts in compression ignition (CI) engines. Most of these combustion concepts, lead towards a lean and low temperature combustion potentially suitable to achieve lower emission and fuel consumption levels compared to conventional diesel combustion. In this framework, Partially Premixed Combustion (PPC) using gasoline as fuel is one of the most accepted concepts. There are numerous studies focused on studying concepts such as PPC from the emissions point of view. Nonetheless, there is a lack of knowledge regarding changes in heat transfer introduced by the use of these combustion concepts. It is worth noting that heat transfer can be considered as a key aspect behind possible engine performance improvements. Thus, the reliable estimation of this parameter is of considerable importance. Additionally, a better understanding of how events such as injection and combustion might affect heat transfer is also relevant.To gain insight into gasoline PPC heat transfer coefficient, its evolution during late compression and early expansion were studied. In particular, this work aims to analyze Turbulent Kinetic Energy (TKE) spatial and temporal evolution influence on heat transfer coefficient. The analysis is based on experimental TKE maps derived from Particle Image Velocimetry (PIV) data. For the heat transfer coefficient estimation a modified Woschni correlation has been used. Results from several injection strategies and a reference motored case have been analyzed. It has been found that injection strategy has a considerable influence on the TKE field and hence on heat transfer coefficient evolution.

A numerical and experimental study of dual fuel diesel engine for different injection timings

The dual-fuel technology has the potential to offer significant improvements in the CO2 emissions from light-duty compression ignition engines, and in this sense, such a concept represents a viable solution to reduce emissions from diesel engines by using natural gas as an alternative fuel. In light duty, high-speed engines, where the combustion event can be temporally shorter, the injection timing plays an important role on the performance and emissions. Following a methodology that has been proposed in previous authors' papers, this article summarizes the results of a combined numerical and experimental study on the effect of injection timing on performance and pollutant fractions of a common rail diesel engine supplied with natural gas and diesel oil. The study of dual-fuel engine carried out in this paper aims at the evaluation of the CFD potential to predict the main features of this particular technology. The experimental investigations allow the validation of the CFD modeling and, at the same time, highlight the major aspects that arise from the actual engine operation with different diesel injection advances. The fluid-dynamic calculations are extremely useful to put into evidence the key phenomena that take place during the dual-fuel operation, say the typical flame propagation throughout the premixed methane–air medium that is activated by the early self-ignition of the diesel fuel. While previous papers have discussed the effect of the NG/diesel fuel ratio, this paper focuses the attention on different conditions that have been induced by varying the injection timing at fixed brake torque and diesel amount. Actually, the start of injection timing can considerably influence the combustion development and therefore THC and NOx fractions production. Calculations making use of the fluent code have been compared with the experimental data and a comparison between full diesel and dual fuel operation has been made, in terms of performance and pollutant levels.

Effect of Premixed Diesel Fuel on Partial HCCI Combustion Characteristics

This study investigated the effects of premixed diesel fuel on the auto-ignition characteristics in a light duty compression ignition engine. A partial homogeneous chargecompression ignition (HCCI) engine was modified from a single cylinder, four-stroke, direct injection compression ignition engine. The partial HCCI is achieved by injecting diesel fuel into the intake port of the engine, while maintaining diesel fuel injected in cylinder for combustion triggering. The auto-ignition of diesel fuel has been studied at various premixed ratios from 0 to 0.60, under engine speed of 1600 rpm and 20Nm load. The results for performance, emissions and combustion were compared with those achieved without premixed fuel. From the heat release rate (HRR) profile which was calculated from in-cylinder pressure, it is clearly observed that two-stage and three-stage ignition were occurred in some of the cases. Besides, the increases of premixed ratio to some extent have significantly reduced in NO emission.

Computational Analysis of Combustion of High and Low Cetane Fuels in a Compression Ignition Engine

Past research has shown that the combustion of low cetane fuels in compression ignition (CI) engines results in higher fuel conversion efficiencies. However, when high-cetane fuels such as diesel are substituted with low-cetane fuels such as gasoline, the engine operation tends to suffer from high carbon monoxide (CO) emissions at low loads and combustion noise at high loads. In this paper, we present a computational analysis of a light-duty CI engine operating on diesel, kerosene and gasoline. These three fuels cover a range of cetane numbers (CNs) from 46 for diesel to 25 for gasoline. Similar to experiments, the model predicted higher CO emissions at low load operation with gasoline. Predictions of in-cylinder details were utilized to understand differences in combustion characteristics of the three fuels. The in-cylinder mass contours and the evolution of model predicted in-cylinder mixture in Φ–T coordinates were then used to explain the emission trends. From the analysis, overmixing due to early single injection was identified as the reason for high CO emissions with low load gasoline low temperature combustion (LTC). Additional simulations were performed by introducing techniques like cetane enhancement, adding hot exhaust gas recirculation (EGR), and variation of the injection scheme. Their effects on low load gasoline LTC were studied. Finally, it is shown that use of a dual pulse injection scheme with hot EGR helped to reduce the CO emissions for low load gasoline LTC while maintaining low NOx emissions.