Single-cylinder Heavy-duty Engine Research Articles

Optimization methodology combining Taguchi design and response surface method to maximize a compression ignition engine efficiency fueled with oxygenated synthetic fuel

This research examines the potential of a synthetic e-diesel and oxymethylene dimethyl ether blend in a heavy-duty single-cylinder engine. The main purpose is to find the optimal engine settings that maximize engine efficiency and minimize emissions. As the first step, a methodology was developed and applied to simplify the engine’s map into five characteristic points to be representative of the World Harmonized Transient Cycle, assigning weights to each load region. This simplification reported low error estimations for fuel consumption and NOx emissions over the cycle. After obtaining the five points, a drop-in analysis was assessed, where the fuel was evaluated with the same settings as diesel, revealing more advanced and shorter combustion with great reductions in soot emissions. Then, a group of three air management and three injection parameters was selected for optimization. A novel methodology combining Taguchi Design and Response Surface Methodology is developed and applied to find the best engine settings. By integrating these two methods, the research reduced the number of required experiments if only one method were used and maintained the goal of achieving higher thermal efficiencies with the new fuel blend compared to the diesel baseline. Significant statistical results were obtained in the Taguchi design, revealing the air management factors that most affected the responses; meanwhile, second-order models with high accuracy helped in finding the best injection parameters. Subsequently, the best settings were experimentally evaluated, and optimal conditions determined by the two methods were validated, confirming the effectiveness of the methodology. Optimization results revealed an improvement of around 2% higher efficiencies for the five tested points while achieving important average reductions of 28% less in NOx with additional decreases in CO, HC, and soot levels, all outperforming traditional diesel benchmarks. Finally, a well-to-wheel analysis using the simplified cycle confirmed a substantial reduction in carbon impact when replacing diesel with this alternative fuel. The successful application of this methodology to recalibrate an engine with an alternative fuel blend shows the potential of using these fuels in existing engines and offers a novel methodology that can be escalated and applied under the engine calibration context.

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

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

Ammonia combustion using hydrogen jet ignition (AHJI) in internal combustion engines

The application of ammonia and hydrogen in internal combustion engines (ICE) is a promising zero-carbon technology. This paper investigates ammonia combustion in ICE using hydrogen multiple-injection jet-ignition (MIJI). The experiment was conducted on a single-cylinder heavy-duty engine with a compression ratio of 17 and a cylinder bore of 123 mm. In the passive jet ignition mode, the minimum hydrogen energy ratio for stable operation of the ammonia-hydrogen engine was 15 %. Using H2 active jet ignition could improve the combustion stability significantly. It was found that engine performance was gradually improved by H2 injection strategy in order of single-injection, double-injection to triple-injection. The triple-injection strategy could achieve a more ideal distribution of ammonia-hydrogen mixture: the first injection forms a homogeneous mixture to increase fuel reactivity; the second injection creates a stratified hydrogen mixture, facilitating rapid flame propagation; the third injection forms a relatively rich mixture in the jet chamber conducive to spark ignition. Through the optimization of the hydrogen injection strategy and spark timing, stable combustion (COV = 1 %) and high thermal efficiency (ITE = 42.5 %) in ammonia-hydrogen engines were achieved, with a minimum hydrogen energy ratio less than 3 %.

Experimental study on engine and emissions performance of renewable diesel methanol dual fuel (RMDF) combustion

Methanol (MeOH) and renewable diesel (RD) are being considered promising alternative fuels for the de-fossilization of internal combustion engines (ICE). This study provides an experimental investigation on the use of both fuels under dual-fuel combustion mode: port fuel injection (PFI) of MeOH and direct injection (DI) of RD. The combustion mode is labeled as RMDF (renewable diesel methanol dual fuel). The experiment was performed in a heavy-duty single-cylinder engine (SCE) equipped with combustion and emissions measurements and analysis for engine efficiency and emissions of soot and NOX (oxides of nitrogen). MeOH substitution rate, which is the mass ratio of injected MeOH fuel to total injected fuels of both MeOH and RD, was varied to study its effect on engine efficiency and emissions. Different MeOH substitutions were tested from low (6.9 bar gIMEP) to full (23.5 bar gIMEP) engine load conditions at a fixed engine speed of 1200 RPM.Test results showed that higher MeOH substitution rates can reduce NOX emissions effectively while improving engine thermal efficiency. However, a higher MeOH substitute rate can result in longer ignition delay at low load, and increased emissions of carbon monoxide (CO) and unburned hydrocarbon (UHC). Increased maximum pressure rise rate (MPRR) at high load condition was observed as the MeOH substitution rate increased. MPRR is not sensitive to the change in MeOH at low load condition. While ignition delay became longer at low load, it was shorter at high load as MeOH substitution rate increased. Overall, the results from this study suggest that RMDF can be considered as an option to achieve a cleaner and more efficient engine. However, further optimization of combustion designs and engine operating strategy need to be considered to improve combustion loss from RMDF emissions, possibly due to the lower reactivity of MeOH.

Effect of Diesel Injection Strategy and Ammonia Energy Fraction on Ammonia-Diesel Premixed-Charge Compression Ignition Combustion and Emissions

The utilization of ammonia as a fuel is one of the effective measures to achieve decarbonization and carbon neutrality in internal combustion engines (ICEs). However, its slow laminar flame speed and high ignition energy limit the efficient application of ammonia-only in ICEs. In this study, based on a heavy-duty single-cylinder engine, the impact of ammonia energy fraction (AEF), start of diesel injection (SODI) timing, and diesel injection pressure (DIP) on combustion and emission characteristics of premixed-charge compression ignition mode under low load conditions was investigated. Combined with three-dimensional simulation, the mechanism of how AEF and diesel injection strategy regulation affected the in-cylinder equivalence ratio and reactivity distribution was analyzed. It was found that increasing the AEF and advancing the SODI timing can improve the homogeneity of mixture. However, the spatial distribution of the OH groups deteriorate continuously. Experimental results indicated that with the used of 50% AEF, 60 MPa DIP, and injecting diesel at −40°CA ATDC, a gross indicated thermal efficiency (ITEg) of 49.7% can be achieved. Compared to the diesel-only mode, the greenhouse gas (GHG) emissions reduced by 44%. To further improve the combustion of ammonia/diesel PCCI mode, the DIP was increased to 100 MPa, which optimized the in-cylinder fuel–air mixing process, improving the homogeneity of the mixture and enhancing the reactivity distribution before the ignition, and enabling faster combustion. As a result, an increase in ITEg to 51.4% with using 100 MPa DIP was achieved, and reduced the GHG emissions by 51% compared to the diesel-only mode.

Investigation of the drop-in capabilities of a renewable 1-Octanol based E-fuel for heavy-duty engine applications

This article presents the results of an investigation of neat 1-Octanol and its blends with Diesel, which can be potential drop-in fuels for heavy-duty compression ignition engines. Fuel blends consisting of 10 %, 20 %, and 30 % 1-Octanol by volume in Diesel, including neat 1-Octanol, were investigated for ignition and combustion performances. The ignition behavior was assessed using a constant-volume combustion-chamber-based ignition tester. The experimental investigation was conducted on a heavy-duty single-cylinder engine by varying the combustion center. In addition, injection-rate shaping was performed to understand the effects of various injection-rate shapes, namely square, ramp, and boot rate shapes, on the performance of neat 1-Octanol.The ignition tester results indicated an increased ignition sensitivity of neat 1-Octanol towards the chamber pressure and temperature compared to that of Diesel. At an elevated chamber temperature (650 °C) and pressure (20 bar), the ignition delay of neat 1-Octanol approaches closer to that of Diesel. Engine experiments revealed an improved thermal efficiency with neat 1-Octanol and its blends by up to 1.2 %, owing to their improved mixture homogenization capabilities. Furthermore, neat 1-Octanol and its blend led to a drastic reduction in smoke and carbon monoxide. In addition, it results in the highest peak during the premixed heat release, and with a square injection-rate shape, an additional minor improvement in thermal efficiency was observed. The relative changes in carbon monoxide and hydrocarbon emissions between the injection-rate shapes were negligible. At higher load, the boot-rate shape results in lower NOx formation than the square-rate shape at an almost identical thermal efficiency. Overall, the 10 % 1-Octanol, 20 % 1-Octanol and 30 % 1-Octanol blends, which fulfill the Cetane number requirements for the given fuel norms, can be used as drop-in fuels, as they exhibit a comparable or even better performance than Diesel.

A Numerical Methodology for the Design of Active Prechambers in Spark-Ignition Engines

ABSTRACT Active prechamber spark-ignition engines are a feasible and effective solution in reducing fuel consumption and pollutant emissions for internal combustion engines. However, reliable and low-cost numerical approaches need to be developed to support and speed-up their industrial design, considering their geometric complexity and the involved multiple-flow length scales. In this work, a computational fluid dynamics (CFD) methodology is presented for the design of active prechambers (APCHs) in spark-ignition engines. It consists of two connected steps. First, the fuel injection process inside the APCH is simulated inside a constant-volume domain, including only the APCH geometry and considering the main chamber (MCH) as boundary condition. Then, the power-cycle is simulated on the whole closed-valves domain (APCH and MCH). A flame area evolution model is used to describe the flame propagation process. Experimental data from a research single-cylinder heavy-duty engine are used to assess the proposed methodology. Different operating conditions are considered, to evaluate the effects produced by variations of the nozzles diameter, the MCH air/fuel ratio and the load. Satisfactory results were achieved, demonstrating that the proposed methodology is consistent and reliable.

A Novel Surrogate Fuel Approach for the Numerical Simulation of Renewable Fuels for the Transport Sector

The use of fuels made from renewable resources can be beneficial in reducing the CO2 emission balance of the existing vehicle fleet. These fuels should be drop-in-capable, i.e., their properties should correspond as far as possible to those of fossil fuels. In addition, they should be able to be blended with conventional fuels. In order to determine the full potential of new renewable drop-in fuels, numerical investigations can make a significant contribution.A novel Surrogate Fuel Approach (SFA) was proposed to perform the numerical simulations for blends of paraffinic diesel fuel and alcohols. A set of modeling and mixing rules were used to estimate and extrapolate the required thermo-physical and physicochemical properties of renewable fuels. The detailed chemical mechanisms for n-dodecane and n-octanol were merged. A systematic reduction of the detailed chemical mechanisms was performed using the Directed Relation Graph with Error Propagation (DRGEP) method. For the selected target species, the reduced mechanism from the DRGEP and lumping method contains ∼31% species and ∼40% reactions as of the merged reaction mechanism. The blended fuel properties and the reduced reaction mechanism were incorporated into the numerical simulations. The surrogate fuel approach was validated for steady-state as well as transient operating conditions using the experimental results obtained from the optical high-pressure chamber (HPC) and a heavy-duty single-cylinder engine (HD-SCE). The HD-SCE testing shows that the 60% B0-Di/40% RF blend increases ITE by ∼2% in absolute values and lower ISCO2, ISCO, ISHC and smoke emissions as compared to Diesel fuel. This is due to the paraffinic fuel structure, the fuel-borne oxygen, the high calorific value, and the high cetane number. The calibrated 3D-CFD spray models show an excellent agreement with experimental data from the optical investigations of different spray characteristic values — Liquid and Gaseous penetration Length, Lift of Length and ignition delay for the 60% B0-Di/40% RF fuel. Further, the pressure traces, heat release rates, and nitrogen oxides (NOX) emissions from the numerical 3D-CFD simulations showed a good agreement with the results from the HD-SCE experiments. Overall, these results support the suitability of the proposed novel surrogate fuel approach for simulating different blends of renewable drop-in fuels.

Impact of Low Reactivity Fuel Type and Energy Substitution on Dual Fuel Combustion at Different Injection Timings

Dual fuel combustion leverages a high-reactivity fuel (HRF) to ignite a premixed low reactivity fuel (LRF)–air mixture to achieve high efficiencies and low engine-out emissions. The difference in the relative amounts of these fuels and in-cylinder fuel reactivity stratification profoundly impacts dual fuel combustion. The effect of increasing LRF energy substitution on dual fuel combustion at various fixed HRF (diesel) quantities was experimentally studied for two different LRFs (natural gas and propane) on a heavy-duty single cylinder engine at a constant intake pressure of 1.5 bar and injection pressure of 500 bar. Further, this effect was studied for three different HRF start of injection (SOI) timings of 310 CAD (50° BTDC), 330 CAD (30° BTDC), and 350 CAD (10° BTDC). For 310 CAD SOI, increasing the LRF substitution at a fixed HRF resulted in higher loads, peak cylinder pressures, and peak apparent heat release rates (AHRR). The onset of low temperature heat release (LTHR) was advanced as the LR fuel flowrate increased at a given pilot quantity for diesel–NG but remained constant for diesel–propane dual fuel combustion at these SOIs due to the impact of propane on the temperature at which the onset of LTHR occurs. The indicated fuel conversion efficiency (IFCE) ranged from 35% at 4 bar IMEPg to 47% at 9 bar IMEPg with NG as the LRF and from 35% at 3 bar IMEPg to 51% at 8 bar IMEPg with propane as the LRF. For 330 CAD SOI, the HC and CO emissions decreased at a higher fixed HRF quantity and an increasing LRF substitution. However, this was accompanied by significantly higher oxides of nitrogen (NOx) emissions for both NG and propane as LRFs. For 350 CAD SOI, increasing the LRF substitution at constant HRF consistently led to a higher second stage AHRR, whereas the first stage AHRR remained relatively unchanged for both NG and propane as LRFs. This was accompanied by higher IFCE for all fixed HRF quantities as LRF substitution was increased. For all SOIs studied, the HC and CO emissions were substantially lower and combustion stability was significantly improved as the LRF substitution (and consequently, the load) was increased. To the best of the authors’ knowledge, the present work is unique in that it involves the first systematic experimental study of the impact of LRF energy substitution at fixed HRF quantities over a range of SOIs, providing comparative results for two different LRFs (NG and propane) on the same engine platform.

Impact of renewable fuels on heavy-duty engine performance and emissions

The transport sector faces two critical issues: a limited supply of fossil fuels and high greenhouse gas (GHG) emissions. Additionally, the demand for freight transport is steadily increasing, ultimately leading to higher GHG emissions. Since these emissions promote climate change, reducing the GHG emissions from the transport sector is necessary. Renewable drop-in fuels can play an essential role in this regard as those are CO2 neutral. Since these fuels come from so-called renewable sources, this represents a way to reduce carbon dioxide emissions from the current vehicle fleet to meet the EU’s Green Deal goals to become climate neutral by 2050. The drop-in fuels from renewable sources and later the purely renewable fuels serve as a bridging technology in this context.With this in mind, experiments were conducted with a Heavy-Duty Single Cylinder Engine (HD-SCE). The effects of four different renewable fuels or fuel blends – 93% RF/7% UCOME, 60% B0-Diesel/40% RF blend, 70% Diesel/30% Octanol blend and 100% Octanol – on engine performance and raw emissions were studied in comparison to fossil Diesel fuel. The investigations were conducted at three different load points — Rated Power (RP), best Brake Thermal Efficiency (BTE) and Cruise Point, covering all the relevant load points for HD engines. For all load points, the use of renewable fuels resulted in lower carbon dioxide (CO2), hydrocarbon (HC), carbon monoxide (CO) and FSN compared to fossil Diesel due to the fuel-borne oxygen and the lower C/H ratio of these alternative fuels. The blend of 60% B0-Diesel-40% RF shows the highest efficiency due to the paraffinic fuel structure, the fuel-borne oxygen, the higher calorific value, and the high cetane number. 100% Octanol resulted in a reduction in FSN by a factor of 3. All renewable fuels show a GHG emission reduction potential of around 2.5% to 5.5% in the Tank-to-Wheel (TtW) analysis.

Experimental and numerical investigation of a direct injection spark ignition hydrogen engine for heavy-duty applications

The H2 internal combustion engine is gaining increasing interest especially for commercial vehicles. Regarding the optimization of the combustion process, results of experimental investigations on a H2 heavy-duty single-cylinder engine in combination with numerical 3D-CFD investigations are presented. In addition to a Direct Injection (DI) Spark Ignited (SI) configuration, Port Fuel Injection (PFI) is explored to provide a reference with near homogeneous cylinder charge. The main objective is to assess a 3D-CFD-RANS framework based on ECFM and state-of-the art sub-models to describe the most important phenomena occurring in H2 spark ignition engines and to support the experimental analysis. Experimental results show that the PFI configuration provides efficiency and emissions benefits at the expense of volumetric efficiency. The proposed CFD model demonstrates the ability to successfully simulate different engine operating conditions for both PFI and DI systems. In particular, it is shown that the charge stratification typical for DI systems is not beneficial for the studied configuration as it increases wall heat losses and NOx formation.

Effects of pre-mixed gas composition on combustion characteristics of micro pilot dual fuel (MPDF) in a heavy-duty dual fuel engine

The effects of premixed gas compositions on the combustion characteristics in micro pilot duel fuel (MPDF) conditions were investigated. Propane, hydrogen, and carbon dioxide gases were added to methane gas, and engine experiments were conducted under various premixed gas compositions. A single-cylinder heavy-duty engine with a combustion chamber volume of 1100 mm3 and compression ratio of 17.0 was used. A 55 kW DC dynamometer was used to operate the single-cylinder dual-fuel engine at a constant engine speed. At high propane mixture ratios, knocking combustion occurred, accompanied by intense engine vibrations, owing to the low octane number of propane. Knocking combustion led to an increase in the combustion variation and ringing intensity (which represents the knocking combustion intensity). In contrast, at high ratios of hydrogen, which has a high octane number, knocking combustion was suppressed, and the speed of combustion was lower than that in the case of high propane mixture ratios. The optimum conditions corresponded to a ringing intensity of 3–5 MW/m2. The addition of even a small amount of propane gas enhanced the engine performances in misfiring conditions. In contrast, a considerable amount of hydrogen gas was required to prevent abnormal combustion because of the low density of hydrogen gas. The presence of carbon dioxide effectively stabilized MPDF combustion by suppressing knocking combustion.

Effects of split injection strategy on the combustion, emission and economic performance of the low-octane gasoline fueled MPCI engines

Application of diesel fueled partially premixed compression ignition (PPCI) engines are limited due to its excessive pressure rise rate at high load. Multiple premixed compression ignition (MPCI) engines fueled with low octane number gasoline (LON) has the potential to operate at both low and high load, while effects of split injection strategy on performance of such engines have not been discovered yet. In the present study, comparisons of LON and commercial diesel are first conducted in a heavy-duty single cylinder engine. Then, pilot injection timing and main injection timing are varied individually to reveal their effects on the combustion, emission, and economic performance of the MPCI engine. Comparing with diesel, MPCI engines with LON merits a low pollutants emission due to the long ignition delay and good volatility of LON. Split injection strategy can reduce the NOx and PM emissions simultaneously for MPCI engine with LON, and also reduce fuel consumption.

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

<div class="section abstract"><div class="htmlview paragraph">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.</div></div>

Potential of miller timing with synthetic diesel fuels on a single cylinder heavy-duty engine

Upcoming emission limits such as Euro VII will make it necessary to further reduce the NOx emission level of internal combustion engines while stricter CO2 limits demand lower fuel consumption. Early closing of the intake valves (Miller timing) leads to reduced combustion temperatures due to lower effective compression ratio, and therefore lower formation and emission of nitrogen oxides. Miller timing is frequently used in gasoline engines, while in Diesel engines it competes with exhaust gas recirculation (EGR). When both measures are applied simultaneously, this may lead to increased emission of soot using standard Diesel fuel, as combustion temperature and oxygen content of the charge become too low. This work shows the investigation of different intake valve timings on an externally supercharged single-cylinder heavy-duty Diesel engine, stationary operated with hydrogenated vegetable oil (HVO), oxymethylene ether (OME), and standard Diesel fuel (DF). The synthetic fuels have a higher cetane number than DF, which supports ignition at lower temperatures. Moreover, OME has a soot-free combustion, which allows an extension of the operating limits without increased emissions. The results show that especially with Miller timing a high-performance turbocharging system is crucial, since higher boost pressure is required to compensate for the filling losses due to the earlier intake closing. The application of a high EGR rate is limited in this case, leading to a trade-off between Miller timing and EGR. All fuels show a reduction in nitrogen oxides of up to 40% with an improved efficiency of more than 3% at a typical road-load point. Measures to reduce ignition delay were found to be necessary, especially for DF. For OME, increased soot formation does not occur when combining Miller timing with low rail pressure, reduced boost pressure or EGR, which promotes simultaneous application of the measures resulting in minimized emissions of nitrogen oxides.

Effects of methane ratio on MPDF (micro-pilot dual-fuel) combustion characteristic in a heavy-duty single cylinder engine

In this study, the characteristics of micro-pilot dual-fuel combustion with respect to the fuel mixture ratio in a single cylinder dual-fuel engine have been investigated. In order to analyze the characteristics of micro-pilot dual-fuel combustion, a metal engine and an optical single cylinder dual-fuel engine were used. The fuel mixture ratio was varied for experimental purposes; the diesel was directly injected into combustion chamber and the methane gas was supplied via intake port. The present study reports that increasing the methane mixture ratio from 0 to 97.67% changes the diesel combustion to pre-mixed combustion. As a result, the peak cylinder pressure was increased from 184 to 198 bar, and the rate of heat release was greatly advanced. In the MPDF condition, the nitrogen oxides emissions were reduced by about 90%p, and the fuel conversion efficiency increased about 5%p because of the low combustion temperature of pre-mixed combustion. However, for the same reason, the hydrocarbon emissions were increased about 95%p. The fastest combustion speed was found form the results of methane mixture ratio between 40 and 80%. In the condition of diesel combustion and micro-pilot dual-fuel combustion, the combustion periods of middle and initial were increased, respectively, resulting in the low combustion speed. The standard deviation of peak cylinder pressure, which represents the combustion variation, was correlated with initial combustion period. While the condition of methane gas mixture ratio between 40 and 80% shows the lowest combustion variation, the highest combustion variation was occurred by MPDF condition. Through the optical engine experiment, it can be found that the cycle to cycle combustion variation is ascribed to the turbulent flow and the variation of ignition position. The combustion images show that the unpredictable characteristics of the ignition position and slow flame propagation speed caused the combustion variation in micro-pilot dual-fuel combustion.

Influence of the diesel pilot injector configuration on ethanol combustion and performance of a heavy-duty direct injection engine

Thanks to its properties and production pathways, ethanol represents a valuable alternative to fossil fuels, with potential benefits in terms of CO2, NOx, and soot emission reduction. The resistance to autoignition of ethanol necessitates an ignition trigger in compression-ignition engines for heavy-duty applications, which in the current study is a diesel pilot injection. The simultaneous direct injection of pure ethanol as main fuel and diesel as pilot fuel through separate injectors is experimentally investigated in a heavy-duty single cylinder engine at a low and a high load point. The influence of the nozzle hole number and size of the diesel pilot injector on ethanol combustion and engine performance is evaluated based on an injection timing sweep using three diesel injector configurations. The tested configurations have the same geometric total nozzle area for one, two and four diesel sprays. The relative amount of ethanol injected is swept between 78 – 89% and 91 – 98% on an energy basis at low and high load, respectively. The results show that mixing-controlled combustion of ethanol is achieved with all tested diesel injector configurations and that the maximum combustion efficiency and variability levels are in line with conventional diesel combustion. The one-spray diesel injector is the most robust trigger for ethanol ignition, as it allows to limit combustion variability and to achieve higher combustion efficiencies compared to the other diesel injector configurations. However, the two- and four-spray diesel injectors lead to higher indicated efficiency levels. The observed difference in the ethanol ignition dynamics is evaluated and compared to conventional diesel combustion. The study broadens the knowledge on ethanol mixing-controlled combustion in heavy-duty engines at various operating conditions, providing the insight necessary for the optimization of the ethanol-diesel dual-injection system.

Effects of ethane addition on diesel-methane dual-fuel combustion in a heavy-duty engine

The present study is a continuation of the previous work by Ahmad et al. (2020), in which ethane (C2H6) enriched diesel-methane (CH4) dual-fuel (DF) combustion was experimentally investigated in a single-cylinder heavy-duty engine. Here, the experiments of ethane enriched DF combustion are carried out with new details together with supporting zero-dimensional (0D) and one-dimensional (1D) chemical kinetics simulations. Three port-fuel injected (PFI) gaseous blends of pure methane with varying ethane concentrations of 0%, 10%, and 20% are used as the main fuels. The PFI gaseous blend provides 97% of the total-fuel energy (TFE), which is ignited by a small 3% (TFE based) pilot diesel. Experiments are performed under lean condition (∅gas = 0.52) for two engine speeds while keeping the TFE and other operating conditions constant. Calculated results from 0D and 1D simulations under engine relevant conditions including theoretical combustion mode analysis (β-curve) are used to deepen the phenomenological understanding of the experimental results. The results reveal that adding ethane into pure methane has minor effects on the pilot-diesel ignition timing. However, ethane addition greatly enhances the ignitability of methane after the start of combustion. Ethane enriched gaseous blends yield higher thermal efficiency and reduce combustion duration compared to pure methane. According to combustion mode analysis, ethane tendency to promote spontaneous autoignition may be one of the reasons for improving overall combustion performance. It is observed that ethane enriched gaseous blends produce lower unburned methane (UB-CH4) and unburned hydrocarbons (THC) accompanied with higher nitrogen oxides (NOx) because of the higher combustion efficiency. Furthermore, ethane addition considerably helps to reduce cycle-to-cycle variations under lean conditions compared to pure methane.

A Computational Investigation of the Impact of Multiple Injection Strategies on Combustion Efficiency in Diesel–Natural Gas Dual-Fuel Low-Temperature Combustion Engines

AbstractDual-fuel diesel–methane low-temperature combustion (LTC) has been investigated by various research groups, showing high potential for emissions reduction (especially oxides of nitrogen oxide (NOx) and particulate matter (PM)) without adversely affecting fuel conversion efficiency in comparison with conventional diesel combustion. However, when operated at low load conditions, dual-fuel LTC typically exhibits poor combustion efficiencies. This behavior is mainly due to low bulk gas temperatures under lean conditions, resulting in unacceptably high carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. A feasible and rather innovative solution may be to split the pilot injection of liquid fuel into two injection pulses, with the second pilot injection supporting CO and UHC oxidation once combustion is initiated by the first one. In this study, diesel–methane dual-fuel LTC is investigated numerically in a single-cylinder heavy-duty engine operating at 5 bar brake mean effective pressure (BMEP) at 85% and 75% percentage of energy substitution (PES) by methane (taken as a natural gas (NG) surrogate). A multidimensional model is first validated in comparison with the experimental data obtained on the same single-cylinder engine for early single pilot diesel injection at 310 crank angle degrees (CAD) and 500 bar rail pressure. With the single pilot injection case as baseline, the effects of multiple pilot injections and different rail pressures on combustion and emissions are investigated, again showing good agreement with the experimental data. Apparent heat release rate and cylinder pressure histories as well as combustion efficiency trends are correctly captured by the numerical model. Results prove that higher rail pressures yield reductions of HC and CO by 90% and 75%, respectively, at the expense of NOx emissions, which increase by ∼30% from baseline still remaining at very low level (under 1 g/kWh). Furthermore, it is shown that postinjection during the expansion stroke does not support the stable development of the combustion front as the combustion process is confined close to the diesel spray core.

Experimental Investigation of Performance and Emissions of Ethanol and n-Butanol Fuel Blends in a Heavy-Duty Diesel Engine

Alcohol fuels are potential alternative fuels for low-temperature combustion concepts in internal combustion engine applications. In this work, 80 vol% of ethanol and 80 vol% of n-butanol are blended with 20 vol% of n-heptane, respectively. These two alcohol fuel blends are investigated in a combustion research unit and a single-cylinder heavy-duty engine to compare the combustion and emission characteristics. The effects of EGR rate and achievable operating load range when using ethanol and n-butanol are the major goals of this investigation. The results show that the ethanol fuel blend requires much higher temperatures to auto-ignite than do the n-butanol blend and diesel. Both alcohol fuel blends show negligible soot emissions in the medium load range when operated with a 40% EGR rate. However, the ethanol fuel blend produces more nucleation mode particles and fewer accumulation mode particles compared to the n-butanol fuel blend under the same operating condition. Furthermore, the particulate size distribution shows that diesel generates more particles with larger particle diameters and thus more soot mass compared to alcohol fuel blends. Still, both alcohol fuel blends can be operated from low to high load with simultaneous reduction of NOx and soot emissions but at the cost of increased HC and CO emissions. The Euro VI-regulated soot mass and particle number are achieved from low to medium-high load for alcohol fuels. Diesel has the great advantage of achieving high combustion efficiency but shows a NOx/soot tradeoff at a high EGR rate. Generally, the ethanol fuel blend yields the lowest gross indicated efficiency in the whole test range compared to diesel and the n-butanol fuel blend due to the necessity of inlet heating, which decreases the thermal efficiency. The n-butanol fuel blend achieves the highest gross indicated efficiency (above 50%) in the medium-high load range.