bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly Efficient and Clean Combustion Engine for Synthetic Fuels
Authors: Kraus Christoph , Thamm Fabian , Retzlaff Mario , Gadomski Bartosch , Fitz Patrick , Härtl Martin , Hoppe Steffen , Jaensch Malte
Published: April 2023

This paper provides an overview of possible engine design optimizations by utilizing highly knock-resistant potential greenhouse gas (GHG) neutral synthetic fuels. Historically the internal combustion engine was tailored to and highly optimized for fossil fuels. For future engine generations one of the main objectives is to achieve GHG neutrality. This means that either carbon-free fuels such as hydrogen or potential greenhouse gas neutral fuels are utilized. The properties of hydrogen make its use challenging for mobile application as it is very diffusive, not liquid under standard temperature/pressure and has a low volumetric energy density. C1-based oxygenated fuels such as methanol (MeOH), dimethyl carbonate (DMC) and methyl formate (MeFo) have properties like conventional gasoline but offer various advantages. Firstly, these fuels can be produced with renewable energy and carbon capture technologies to be GHG neutral. Secondly, the C1-based fuels burn with significantly less pollutant emissions. A third advantage is the high knock resistance of those fuels. This inherits a drastic efficiency potential for spark ignition engines as the compression ratio and therefore the potential thermal efficiency can be directly increased. In the single cylinder engine, a compression ratio (CR) of ~20:1 is investigated proving the high knock resistance as well as the efficiency potential of MeOH and a mixture containing 65 vol% DMC and 35 vol% MeFo (C65F35). Special attention is paid to the direct injection strategy, which utilizes up to quadruple injections and 35MPa fuel pressure. Later on, a more moderate CR increase to 15:1 with a CFD optimized piston design is investigated at a state of the art four-cylinder engine (4CE) utilizing C65F35. The whole engine map is presented proving the real-world usability and efficiency potential of this fuel type in combination with the optimized piston. WLTC and RDE tests were performed, underling both the practicality and the efficiency potential in dynamic conditions. The 4CE tests are rounded off by showcasing the potential of lean operation with two different high-energy ignition systems (Corona and passive pre-chamber ignition). The performance investigation on both engines is accompanied by emission measurements utilizing standard exhaust analyzers, an FTIR-device and particle number counting systems.
Understanding Interaction between Reactive Jets in Pre-Chamber Ignition of Gaseous Fuel
Authors: Zhang Yixiao , Ma Xiao , Mao Jianshu , Fang Yuwen , Li Yanfei , Shuai Shijin
Published: April 2023

In order to improve the ignition capacity and burning rate for spark-ignited engines, pre-chamber jet ignition is a promising technique to achieve fast premixed combustion and low pollutant emissions. However, few studies focus on the interaction between multiple reacting (i.e. flamelet) or reacted (i.e. radical) jets, its effect on ignition, exotherm and flow behaviors also remain to be revealed. This paper investigated two types of jet interaction under different pre-chamber structures, including the jet-crossing and unequal nozzle designs. Optical experiments under different conditions were conducted in a constant volume combustion chamber with CH4 as fuel, using simultaneous high speed schlieren and OH* chemiluminescence method. Meanwhile, computational fluid dynamics (CFD) simulations with CH4 and NH3/CH4 blend fuels were carried out using Converge software to provide further insights of turbulent flow and ignition process. For the jet-crossing structure, it was found that ignition can be controlled in the jet-crossing zones under different initial conditions, with more repeatable and stable developments than the parallel structure case. The cross angles in the range of 20°-30° with respect to the pre-chamber axis show similar performances and more favorable for ignition control overall, while the cross region too closed to the nozzles reduce the overall burning rate. The simulation results show that local Da number around ignition zone is in the range of 0.2-0.4, and with the addition of NH3, the flame regime is located in thickened and broken reaction zone during early jet evolution. For the unequal nozzle design with the diameter of 2 mm and 4 mm, the ignition delay time of the radical jet will be reduced by 60 % than the two equal nozzles with the diameter of 2 mm, because of the suppression of quenching in presence of the flame jet. And the flame expansion in horizontal direction is also improved. In addition, the ignition patterns are also influenced by different equivalence ratios due to the changes of temporal sequence of two jet evolution.
Investigation of Solenoid-Controlled Piston Cooling Jet Benefits for a 1.5l, 3 Cylinder Tcic Diesel Engine
Authors: vinaya murthy Vijayendra , Sithick basha Abubakker , Dharan R Bharani , Rengaraj Chandrasekaran , VIGNESH A. C.
Published: April 2023

The fuel economy of the internal combustion engine becomes progressively critical, especially with the stringent standards set by the government. To meet the government norms such as CAFE (Corporate Fuel Average Economy), different technologies are being explored and implemented in internal combustion engines. Several technologies such as variable oil pump, map controlled PCJ (Piston Cooling Jet), variable or switchable water pump & ball bearing turbocharger etc. This study investigates the effectiveness of implementing map-controlled PCJ implemented for a 1.5-litre 3-cylinder diesel engine.

PCJ’s are major consumers of oil flow and map-controlled PCJ is used by many OEM’s e.g., Ford EcoSport to reduce the oil pump flow. In map-controlled PCJ, the oil to the PCJ is controlled using a solenoid valve. The solenoid valve can be completely variable or ON/OFF type. In our application, the ON/OFF type solenoid value is used to regulate the oil flow to PCJ. Conventionally, the oil to the PCJ is supplied at all operating conditions of the engine, even when the piston temperature is within the material acceptable limit. This adds to the parasitic loss of the internal combustion engine, due to the high friction power consumed by the oil pump to meet the oil flow rate requirement. Using the solenoid-controlled PCJ along with Variable Displacement Oil Pump (VDOP), the flow to the PCJ can be shut down at certain operating conditions such as high speed, and low load conditions. Using the VDOP, the total oil flow rate can be reduced whenever there is no flow to the PCJ, this will help to reduce engine friction load & improve the overall fuel economy.

The objective of the paper is to show the systemic approach, design modifications & challenges involved in the implementation of the map controlled PCJ. The final engine with the map-controlled PCJ along with VDOP is evaluated in the NEDC (New European Driving Cycle) drive cycle to understand the benefits & an overall fuel economy of 1 – 2 % was observed. Results are discussed in detail, which have enabled to take required decision on implementation of Map Controlled PCJ in the specific engine application.
Isolated Low Temperature Heat Release in Spark Ignition Engines
Authors: White Samuel , Bajwa Abdullah , Leach Felix
Published: April 2023

Low temperature heat release (LTHR) has been of interest to researchers for its potential to mitigate knock in spark ignition (SI) engines and control auto-ignition in advanced compression ignition (ACI) engines. Previous studies have identified and investigated LTHR in both ACI and SI engines before the main high temperature heat release (HTHR) event by appropriately curating the in-cylinder thermal state during compression, or in the case of SI engines, timing the spark discharge late to reveal LTHR (sometimes referred to as pre-spark heat release). In this work, LTHR is demonstrated in isolation from HTHR events. Tests were run on motored single-cylinder engines and inlet air temperatures and pressures were adjusted to realise LTHR from n-heptane and iso-octane (2,2,4-trimethylpentane) without entering the HTHR regime. LTHR was observed for a lean n-heptane-air mixture at inlet temperatures ranging from 60°C to 100°C and inlet pressures of 0.9 bar (absolute). For temperatures below 60°C LTHR was not detected and for temperatures above 100°C measurements could not be taken due to the presence of HTHR. No LTHR was detected for iso-octane at 0.9 bar inlet pressures for the same conditions. Following predictions from chemical kinetics modelling in CHEMKIN (and previous studies), intake pressures were increased to 1.1 bar and 1.5 bar, which successfully led to the realisation of LTHR from iso-octane. The effect of temperature, pressure, and engine speed on the presence, intensity and phasing of LTHR are presented alongside pressure-temperature trajectories of the in-cylinder gases to explain the trends.
Increasing Engine Efficiency with Hydrogen Assisted Lean Burn Operation on a Small Bore, Long Stroke DISI Engine
Authors: Wenz Erich , Eilts Peter
Published: April 2023

Internal combustion engines fall under increased environmental and social pressure. However, they will still play an important role in future transport, especially in hybrid propulsion systems. As a consequence, efficiency of SI engines has to be further increased. Lean burn operation provides a promising way to reach this target.

An extremely downsized SI single cylinder research engine is used for the investigations. The engine features a stroke-to-bore ratio of 1.5, leading to higher piston speeds and hence increased tumble motion. The resulting increase in turbulent flame speed supports sufficient combustion performance of diluted mixtures. Although the mentioned provisions increase combustion stability for lean burn operation the reachable relative air/fuel ratio is limited. In order to extend the lean burn capabilities of the engine (λ ≥ 2.0) and further exploit the efficiency advantages of this combustion process the engine is upgraded with a hydrogen port fuel injection. With its high laminar flame speeds and low demanded ignition energy, hydrogen acts as a good combustion enhancer in order to achieve the aforementioned targets.

The conducted measurements show that small amounts of hydrogen are sufficient to reach relative air/fuel ratios of λ ≥ 2.0 for all investigated operating points. The increase in lean burn operation is accompanied by an increase of the indicated efficiency. The investigations reveal furthermore that efficiency does not peak with the highest reachable relative air/fuel ratio. This results in the highest achieved indicated efficiency of ηi = 45.6% at a relative air/fuel ratio of λ = 1.9.
Comparison of Water Dilution Effects on Spark-Ignition Engine Performance and Emissions using Hydrous Fuel Blends and Discrete Water Injection
Authors: Voris Alex , Lundberg Matthew , Puzinauskas Paulius
Published: April 2023

Modern water injection systems typically deliver water separately from the primary fuel system using a discrete injector either through the intake port or directly to the cylinder. Recently, however, water dilution strategies using fully hydrous fuel systems have been receiving increased attention. Hydrous fuels are water and liquid fuel blends that are fully mixed prior to delivery to the combustion system. Removing water from naturally hydrous fuels such as ethanol requires large amounts of energy; consequently, it is possible to combine water injection with more economical production by leaving some amount of water in the fuel. This paper compares experimentally the water dilution effects on the combustion and emissions characteristics and overall engine performance when delivering the water through either a hydrous fuel blend or discrete port water injection.

A 2.4L 4-cylinder NA GDI engine was used in experimental testing. The engine was controlled using an aftermarket ECU interfaced with OEM components and a laboratory-grade wide-band oxygen sensor for equivalence ratio quantification and feedback. The results indicated that for brake measurements the type of water addition affects combustion sufficiently enough to be measured and quantified. ISFC reduction ranged between 0.5 and 2% for water injection and 0.5 and 3% for hydrous fuel. Combustion stability tended to be not strongly affected or degraded by water addition. Combustion analysis demonstrated retarded combustion timings and reduced peak pressures of up to 8.5% for all water dilution cases with the largest reductions at the highest speed and load points. Emissions effects showed mixed results that depended on both speed and type of water addition.
An In-Cylinder Imaging Study of Pre-chamber Spark-Plug Flame Development in a Single-Cylinder Direct-Injection Spark-Ignition Engine
Authors: Zhu Chenyi , Chakrapani Varun , Wooldridge Margaret
Published: April 2023

Prior work in the literature have shown that pre-chamber spark plug technologies can provide remarkable improvements in engine performance. In this work, three passively fueled pre-chamber spark plugs with different pre-chamber geometries were investigated using in-cylinder high-speed imaging of spectral emission in the visible wavelength region in a single-cylinder direct-injection spark-ignition gasoline engine. The effects of the pre-chamber spark plugs on flame development were analyzed by comparing the flame progress between the pre-chamber spark plugs and with the results from a conventional spark plug. The engine was operated at fixed conditions (relevant to federal test procedures) with a constant speed of 1500 revolutions per minute with a coolant temperature of 90 oC and stoichiometric fuel-to-air ratio. The in-cylinder images were captured with a color high-speed camera through an optical insert in the piston crown. The images showed plumes of reacting gases originating from the pre-chamber orifices and the subsequent flame development in the main combustion chamber of the engine. Flame characteristics were quantified from the images. Quantitative analysis of the images showed all the pre-chamber spark plugs consistently yielded faster flame development (approximately 4.7 CAD) compared with flames created by the conventional spark plug. The flame fronts from the pre-chamber spark plugs were 1.54-2 times larger than those from the conventional spark plug. The imaging data also showed significant cycle-to-cycle variability during the initial stage of the flame development from the pre-chambers with smaller/later jets for some cycles. However, the flame progress recovered rapidly to more uniform propagation later in the cycles. The different pre-chamber geometries did not lead to significant differences in the combustion characteristics at the studied conditions, although the pre-chamber with asymmetric orifice sizes yielded slightly larger variability and delayed flame development compare with the other pre-chamber designs. The relatively modest effects of the different pre-chamber designs are attributed to potentially offsetting changes in the dominant physical mechanisms affecting the ignition process at the conditions studied.
Effective Ignition of Lean Methane/Hydrogen Mixture in a Rapid Compression Machine
Authors: Yu Xiao , Jin Long , Reader Graham , Wang Meiping , Zheng Ming
Published: April 2023

The use of renewable natural gas and green hydrogen can significantly reduce the carbon footprint of engines. For future spark ignition engines, lean burn strategy and high compression ratio need to be adopted to further improve thermal efficiency, reducing energy consumption. The efficacy of the ignition system is essential to initiate self-sustainable flame under those extreme conditions. In this work, a rapid compression machine is employed to compress air-fuel mixture to engine-like boundary conditions before the spark event to experimentally investigate the ignition and combustion characteristics of the methane-air mixtures under extreme lean conditions. Hydrogen is also added to support the ignition process and enhance flame propagation speed. Lean methane-air mixtures with excess air ratio up to 2.8 are used, with 10 vol% hydrogen addition into the methane fuel. The ignition criteria under various ignition strategies are explored. Both in-cylinder pressure and high-speed direct imaging are collected to analyze combustion parameters, such as heat release rate and flame propagation speed. The impact of discharge current amplitude and duration on the lean burn limit of the fuel-air mixture is investigated.
Exploring the EGR Dilution Limits of a Pre-Chamber Ignited Heavy-Duty Natural Gas Engine Operated at Stoichiometric Conditions - An Optical Study
Authors: Rajasegar Rajavasanth , Srna Ales , Novella Ricardo , Barbery Ibrahim
Published: April 2023

Pre-chamber spark ignition (PCSI) systems have been proven to improve combustion stability in highly-diluted and ultra-lean natural gas (NG) engine operation by providing spatially distributed ignition initiated by multiple turbulent flame-jets that lead to faster combustion compared to conventional spark ignition. This work investigates the physico-chemical processes that drive the ignition and subsequent combustion in the presence of combustion residuals (internal EGR) within the pre-chamber at varying EGR levels. The over-arching goal is to improve the dilution tolerance of PCSI systems for stoichiometric-operation of on-road heavy-duty natural gas engine. To this end, experiments were performed in a heavy-duty, optical, single-cylinder engine to explore the EGR dilution limits of a pre-chamber, spark-ignited, NG engine operated under stoichiometric conditions. A special skip-fire sequence is utilized to distinguish the effects of in-cylinder combustion residuals from external EGR. Optical diagnostics involving high-speed OH* chemiluminescence imaging and infrared (IR) imaging are acquired simultaneously to probe the ignition, development of pre-chamber jets and the subsequent combustion behavior of the main-chamber charge under various EGR dilution rates. The imaging results and the thermodynamic analysis show that the presence of combustion residuals within the pre-chamber lead to slower spark kernel development resulting in lower ΔP, retarded main-chamber ignition and subsequently slower main-chamber combustion. Cycle-to-cycle variations and tendency to misfire increased with increasing EGR dilution, with combustion residuals making this effect more pronounced. Advancing the spark timing, despite lowering ΔP (due to reduced fuel mass in the pre-chamber and increasing back pressure) can sufficiently compensate for reduced [O2] at low to moderate EGR levels. Failed re-ignition of pre-chamber jets is the main cause of increased cycle-to-cycle fluctuations and misfire under the tested conditions.
The Influence of Ignition Control Parameters on Combustion Stability and Spark plug Wear in a Large Bore Gas Engine
Authors: Saha Anupam , Ojanperä Ari-Matti , Hyvonen Jari , Aengeby Jakob , Tidholm Johan , Andersson Oivind , Tunestal Per
Published: April 2023

The paper presents novel studies on the impact of different ignition control parameters on combustion stability and spark plug wear. First, experimental results from a 32.4-liter biogas fueled large bore single cylinder spark ignition engine are discussed. Two different ignition systems were considered in the experiment: a DC inductive and an AC capacitive. The spark plugs used in the experiment were of dual-iridium standard J-gap design of different electrode gaps. Test results show the importance of different degrees of freedom to control a spark. A robust ignition is found to be achieved by using a very short spark duration, which in turn reduces total energy discharge at the gap. Further observations reveal that once a stable and self-propagating flame kernel is developed, it becomes independent of the spark energy further added to the gap. Finally, results from the spark plug wear tests using a pressurized rig chamber are discussed. It is found that an excessive spark energy discharge at the gap contributes to high erosion of spark plug electrodes, which is not desirable. However, spark energy is not the only factor affecting spark plug erosion. It is also the type of spark discharge (DC/AC) that governs the electrode wear over time. Therefore, the advantage of an AC spark discharge over a DC spark has been well established through the experimental results. The inherent property of an AC spark is found to be significantly slowing down electrode wear over time, hence increasing the service life of a spark plug.
An Optical Study of the Effects of Diesel-like Fuels with Different Densities on a Heavy-duty CI Engine with a Wave-shaped Piston Bowl Geometry
Authors: Gong Miaoxin , Derafshzan Saeed , Richter Mattias , Hemdal Stina , Eismark Jan , Andersson Oivind , Lundgren Marcus
Published: April 2023

The novel wave-shaped bowl piston geometry design with protrusions has been proved in previous studies to enhance late-cycle mixing and therefore significantly reduce soot emissions and increase engine thermodynamic efficiency. The wave-shaped piston is characterized by the introduction of evenly spaced protrusions around the inner wall of the bowl, with a matching number with the number of injection holes, i.e., flames. The interactions between adjacent flames strongly affect the in-cylinder flow and the wave shape is designed to guide the near-wall flow. The flow re-circulation produces a radial mixing zone (RMZ) that extends towards the center of the piston bowl, where unused air is available for oxidation promotion. The waves enhance the flow re-circulation and thus increase the mixing intensity of the RMZ. This flame-wall interaction is related to the momentum of the injected fuel sprays and therefore it is reasonable to investigate the impact of fuels of different densities that contain varied momentums. Conventional diesel and n-Heptane are tested in a single-cylinder optical heavy-duty compression ignition engine, as the fuels have similar characteristics but different densities. The spray and combustion processes are visualized by natural luminescence, captured by high-speed video. The experiment results indicate that there is a correlation between fuel densities and the flame-wall interaction.
Understanding Hydrocarbon Emissions to Improve the Performance of Catalyst-Heating Operation in a Medium-Duty Diesel Engine
Authors: Cho Seokwon , Wu Angela , Lopez Pintor Dario
Published: April 2023

To cope with regulatory standards, minimizing tailpipe emissions with rapid catalyst light-off during cold-start is critical. This requires catalyst-heating operation with increased exhaust enthalpy, typically by using late post injections for retarded combustion and, therefore, increased exhaust temperature. However, retardability of post injection(s) is constrained by acceptable pollutant emissions such as unburned hydrocarbon (UHC). This study provides further insight into the mechanisms that control the formation of UHC under catalyst-heating operation in a medium-duty diesel engine, and based on the understanding, develops combustion strategies to simultaneously improve exhaust enthalpy and reduce harmful emissions.

Experiments were performed with a full boiling-range diesel fuel (cetane number of 45) using an optimized five-injections strategy (2 pilots, 1 main, and 2 posts) as baseline condition. Time-resolved UHC measurements in the exhaust port with varying injection timings were used to analyze effects of each injection on UHC emissions. Results show that reducing the ignition delay of the second post injection while keeping its injection timing consistent is very effective to improve UHC emissions without penalizing the exhaust enthalpy. The two pilot and main injections were block-shifted to increasingly retarded timings, resulting in improved exhaust enthalpy, CO and NOx emissions without penalty in UHC emissions, but with significantly higher soot emissions and lower thermal efficiency. To overcome this, an enhanced combustion strategy adopting additional injection(s) is proposed, which consists of a main combustion event near top dead center to increase the in-cylinder temperature, a series of short injections to counteract the expansion effect on temperature, and a large post injection to maximize the exhaust heat. As the result, the proposed strategy successfully improves the exhaust enthalpy and thermal efficiency while suppressing UHC, CO and NOx emissions, therefore, enabling more retarded timings of post injection(s).
Exploration of Fuel Property Impacts on the Combustion of Late Post Injections Using Binary Blends and High-Reactivity Ether Bioblendstocks
Authors: Subramanian Srinath , Rothamer David
Published: April 2023

In this study, the impacts of fuel volatility and reactivity on combustion stability and emissions were studied in a light-duty single-cylinder research engine for a three-injection catalyst heating operation strategy with late post-injections. N-heptane and blends of farnesane/2,2,4,4,6,8,8-heptamethylnonane were used to study the impacts of volatility and reactivity. The effect of increased chemical reactivity was also analysed by comparing the baseline #2 diesel operation with a pure blend of mono-ether components (CN > 100) representative of potential high cetane oxygenated bioblendstocks and a 25 vol.% blend of the mono-ether blend and #2 diesel with a cetane number (CN) of 55. At constant reactivity, little to no variation in combustion performance was observed due to differences in volatility, whereas increased reactivity improved combustion stability and efficiency at late injection timings. Fuels with higher reactivity were found to reduce engine-out hydrocarbon and carbon monoxide emissions while also achieving stable combustion at post-injection timings later than those achievable with #2 diesel fuel. The pure ether blend had the latest achievable post-injection timing of +30.5 CAD while still maintaining stable combustion (coefficient of variation of gross-indicated mean effective pressure < 5%). With post-injection timing adjusted to achieve a matched exhaust temperature of 300 °C, the ether-diesel CN 55 blend was observed to have slightly higher thermal efficiency in comparison to the baseline #2 diesel fuel. The results also indicate that cetane number may serve as a good indicator of combustion characteristics at late injection timings used for aftertreatment thermal management operation.
Meeting Phase-2 GHG and Ultra-Low NOx Emissions with Conventional Engine Design for Light Heavy-Duty Applications
Authors: Kadam Vaibhav , Mayilvaganan Arvind , Desai Chintan , Vernham Bruce
Published: April 2023

Increasing concerns due to global warming have led to stringent regulation of greenhouse gas (GHG) emissions from diesel engines. Specifically, for GHG phase-2 regulation (2027), more than 4% improvement is needed when compared to phase-1 regulation (2017) in the light heavy-duty (LHD) diesel engine category. At the same time, California Air Resources Board (CARB) and Environmental Protection Agency (EPA) have proposed the new Low NOx standards that require up to 90% reduction in tailpipe (TP) NOx emissions in comparison to the current TP NOx standards that were implemented in 2010. In addition, CARB and EPA have proposed new certification requirements – Low Load Cycle (LLC) and revised heavy-duty in-use testing (HDIUT) based on the moving average window (MAW) method that would require rigorous thermal management. Hence, strategies for simultaneous reduction in GHG and TP NOx emissions are required to meet future regulations.

This paper presents potential pathways to achieve the GHG phase-2 and the ultra-low NOx (ULN) regulations with minimum changes in engine design, while meeting the constraints that need to be considered for engine performance stability, component durability, and vehicle drivability. Experimental evaluations were performed focusing on transient cycles such as heavy-duty Federal Test Procedure (hereafter referred as FTP), LLC, and custom transient cycles for HDIUT assessment. We used a model-year (MY) 2021 production Isuzu diesel engine and an advanced dual-dosing aftertreatment system comprising of a close-coupled SCR (ccSCR), diesel oxidation catalyst (DOC), diesel particulate filter (DPF), selective catalytic reduction (SCR), and Ammonia Slip Catalyst (ASC). Conventional thermal management techniques such as multi-injection, intake, and exhaust throttling were implemented to achieve the emissions targets. In addition to the proposed system design, this paper presents following test results from a full-scale system evaluation:

1
Achieve rapid and sustained turbine-out exhaust temperatures (>200°C) while meeting the engine-out emissions constraints for soot and total hydrocarbon (THC) emissions.

2
A summary of TP NOx, TP N2O and GHG emissions over a composite FTP and LLC.

3
HDIUT assessment results and observations for LLC and custom transient cycles.

4
Robustness evaluation of TP NOx emissions for composite HDT, LLC and custom transient cycles by imposing component variations.
Experimental Investigation of Cycle-to-Cycle Variations in Homogeneous Charge Compression Ignition Engine Fueled with Methanol Using Wavelets
Authors: Yadav Ratnesh Kumar , Saxena Mohit Raj , Maurya Rakesh Kumar
Published: April 2023

The development of automotive engines continues to be determined by gradually more stringent emission norms including CO2 emissions and fuel consumption. To fulfill the simultaneous emission requirements for near-zero pollutants and low CO2 levels, several research studies are currently being carried out around the world on new engine combustion process, such as Homogeneous Charge Compression Ignition (HCCI). In HCCI engines, combustion rate, and ignition timing are dominated by physical and chemical properties of fuel/air/residual gas mixtures, boundary conditions including ambient temperature, pressure, and humidity, and engine operating conditions such as load, speed, etc. Higher cycle-to-cycle variations are observed in HCCI combustion engines due to the large variability of these factors. The cyclic variations in the HCCI engine are investigated on a modified four-stroke, four-cylinder engine. The HCCI combustion mode is tested with methanol fuel. This study presents the cyclic combustion analysis of the HCCI engine using statistical and Wavelet Transform techniques. The cyclic variations are characterized under different operating conditions such as relative air-fuel ratios (λ), intake air temperature (Ti), and engine speed (N). The wavelet analysis results indicate that cyclic variations in IMEP and combustion phasing (CA50) occur at different frequencies. Results indicate that with an increase in the Ti, the variations in IMEP are shifted from low periodicity to high periodicity. The high periodicity variations for higher Ti operation are found due to the too advanced CA50 position (before TDC position). Global wavelet spectrum results depict that peak power decreases with an increase in Ti and λ which implies the reduction in cyclic combustion variations.
Investigation of Premixed Fuel Composition and Pilot Reactivity Impact on Diesel Pilot Ignition in a Single-Cylinder Compression Ignition Engine
Authors: Tyrewala Daanish , Rothamer David , Ghandhi J.
Published: April 2023

This work experimentally investigates the impact of premixed fuel composition (methane/ethane, methane/propane, and methane/hydrogen mixtures having equivalent chemical energy) and pilot reactivity (cetane number) on diesel-pilot injection (DPI) combustion performance and emissions, with an emphasis on the pilot ignition delay (ID). To support the experimental pilot ignition delay trends, an analysis technique known as Mixing Line Concept (MLC) was adopted, where the cold diesel surrogate and hot premixed charge are envisioned to mix in a 0-D constant volume reactor to account for DPI mixture stratification. The results show that the dominant effect on pilot ignition is the pilot fuel cetane number, and that the premixed fuel composition plays a minor role. There is some indication of a physical effect on ignition for cases containing premixed hydrogen. The results also show that the HC and CO emissions for the methane/ethane and methane/propane mixtures decrease despite an increase in the molar carbon content of the fuel with substitution of methane. For the methane/hydrogen mixture, the decrease is caused by both the reduction in carbon content and the improvement in background mixture reactivity.
Effect of Standard Tuning Parameters on Mixture Homogeneity and Combustion Characteristics in a Hydrogen Direct Injection Engine
Authors: LOW-KAME Jean , Oung Richard , Meissonnier Guillaume , Da Graca Mathieu , Doradoux Laurent , Foucher Fabrice
Published: April 2023

Dihydrogen, as a zero CO2 fuel, is a strong candidate for internal combustion engine to limit global warming. This study shows the impact of standard tuning parameters on mixture homogeneity and combustion characteristics. A 2.2L Diesel engine on which the head was reworked to allow side mounted direct injector and central mounted spark plug was selected. The discussed tests were made at low engine speed and partial load. A spark advance sweep at different air-fuel ratios (λ) was conducted. The exponential relation between λ and NOx emissions is highly marked and extremely low NOx emissions up to 1.7 g/kWh at minimum spark advance for maximum brake torque can be measured. A λ sweep was performed at different starts of injection (SOI). The results show that, depending on the engine speed, a later SOI might lead to lower NOx emissions. For a λ setpoint of 1.8, at 1500 rpm, late SOI leads to 30% higher NOx emissions where at 2500 rpm these emissions are 26% lower. This assessment is explained by the cycle-to-cycle variations. Finally, the second λ sweep, where the rail pressure (Prail) was varied, reveals that maximizing the Prail does not necessarily lower down NOx emissions. At 2500 rpm of engine speed, for richer mixtures than λ = 1.8, the higher Prail leads to higher NOx emissions. Having a lower Prail might lead to a slightly leaner mixture near the spark plug at spark timing. This effect extends the ignition delay thus lower the NOx emissions.
Challenges and Opportunities with Direct-Injection Hydrogen Engines
Authors: Kalaskar Vickey , Conway Graham , Handa Gaurav , Joo Shinhyuk , Williams Daniel
Published: April 2023

Stringent emissions regulations and the need for lower tailpipe emissions are pushing the development of low-carbon alternative fuels. H2 is a zero-carbon fuel that has the potential to lower CO2 emissions from internal combustion engines (ICEs) significantly. Moreover, this fuel can be readily implemented in ICEs with minor modifications. Batteries can be argued to be a good zero tailpipe emission solution for the light-duty sector; however, medium and heavy-duty sectors are also in need of rapid decarbonization. Current strategies for H2 ICEs include modification of the existing spark ignition (SI) engines to run on port fuel injection (PFI) systems with minimal changes from the current compressed natural gas (CNG) engines. This H2 ICE strategy is limited by knock and pre-ignition. One solution is to run very lean (lambda >2), but this results in excessive boosting requirements and may result in high NOx under transient conditions. The volumetric efficiency of the engine is also reduced in a port-fueled application due to the low volumetric energy density of H2 which displaces fresh air. A novel mixing-controlled combustion strategy is proposed that significantly reduces the propensity of abnormal combustion at stoichiometric air/fuel ratios while also alleviating the need for extreme boosting.

The study was conducted on a pent-roof spark-ignited single-cylinder engine modeled from a large-bore medium-duty engine. A direct injection (DI) system capable of injecting H2 at 170 bar was integrated into the cylinder head. Both, lean and stoichiometric operation of the engine was explored in conjunction with various injection strategies. At a constant load of 8 bar at 1000 rpm test condition, it was shown that a homogenous split-injection strategy, where 50% of the total fuel mass was injected a few degrees after spark timing, was beneficial in NOx reduction while a stratified single-injection strategy exhibited the best thermal efficiency. Further, the results indicated that a stratified combustion strategy was able to increase the knock-limited load of the engine from 3.7 to 8.4 bar gIMEP load at 1000 rpm. This strategy also demonstrated increased efficiency compared to a homogeneous combustion mode and produced lower NOx at comparable loads. The diffusion-like combustion enabled by post-spark injection successfully demonstrated further knock mitigation and NOx reduction but was limited in performance due to challenges associated with in-cylinder mixing and DI injector flow rate.
Non-Intrusive Accelerometer-Based Sensing of Start-Of-Combustion in Compression-Ignition Engines
Authors: Reisetter Mitchell , Herzog Joshua , Amezcua Eri , Kim Kenneth , Kweon Chol-Bum , Rothamer David
Published: April 2023

A non-intrusive sensing technique to determine start of combustion for mixing-controlled compression-ignition engines was developed based on an accelerometer mounted to the engine block of a 4-cylinder automotive turbo-diesel engine. The sensing approach is based on a physics-based conceptual model for the signal generation process that relates engine block acceleration to the time derivative of heat release rate. The frequency content of the acceleration and pressure signals was analyzed using the magnitude-squared coherence, and a suitable filtering technique for the acceleration signal was selected based on the result. A method to determine start of combustion (SOC) from the acceleration measurements is presented and validated. In-cylinder pressure (used to calculate heat release rate) and accelerometer data were collected on a 1.9-L compression-ignition direct-injection engine (Z19DTH) over a wide range of speeds (1000-3250 RPM) and loads (2-8 bar IMEPg), for single- and double-injection strategies, and for fuels of several different cetane numbers (35.5 and 48.5). The relationship between engine block acceleration and the time derivative of heat release rate was verified using the experimental results and indicates that unsteadiness in the rate of heat release is the driving factor for the engine block acceleration signal. The accelerometer-based method developed allows detection of SOC for the main injection with a root mean square error less than 0.75 CAD for the range of conditions tested in this work.
Effects of Ultra-High Injection Pressure and Flash Boiling Onset on GDI Sprays Morphology
Authors: Duronio Francesco , Allocca Luigi , Montanaro Alessandro , Ranieri Stefano , De Vita Angelo
Published: April 2023

Ultra-high injection pressures, as well as flash-boiling occurrence, are among the most important research fields recently explored for improving Gasoline Direct Injection (GDI) engine performance. Both of them play a key role in the enhancement of the air/fuel mixing process, in the reduction of tailpipe pollutant emissions, as well as in the investigation of new combustion concepts. Injector manufacturers are even more producing devices with ultra-high injection pressures capable of working with flashing sprays. Flash-boiling of fuel sprays occurs when a super-heated fuel is discharged into an environment whose pressure is lower than the saturation pressure of the fuel and can dramatically alter spray formation due to complex two-phase flow effects and rapid droplet vaporization. In GDI engines, typically, it occurs during the injection process when high fuel temperatures make its saturation pressures higher than the in-cylinder one. Flash boiling significantly affects the spray structure and fuel-air mixture formation with, potentially, if spray collapse is avoided (with the consequent risk of spray-wall impingement), positive consequences for the engine performance and pollutant emissions. So, this work proposes a combined experimental and numerical characterization of the spray issued by a multi-hole device to highlight the combined role of the injection pressure (up to 700 bar) and the flash boiling occurrence on the spray morphology. Experimental observations of the spray were performed using the Mie-scattering technique. Collected data allowed to evaluate the capabilities of an Eulerian-Lagrangian code in reproducing the injection processes. CFD models for flashing and non-flashing conditions were developed featuring specific breakup and vaporization models suitable for flashing sprays. The numerical model achieves a pretty good level of agreement with the experimental data, and, in particular, it highlights the importance of injection pressure in avoiding spray collapse.
Optical Investigation of the Diesel Spray Characteristics and Spray Geometry Prediction Model by Artificial Neural Network
Authors: Cheng Qiang , Ahmad Zeeshan , Grahn Viljam , Hyvonen Jari , Kaario Ossi , Larmi Martti
Published: April 2023

Spray evolution in diesel engines plays a crucial role in fuel-air mixing, ignition behavior, combustion characteristics, and emissions. There is a variety of phenomenological spray models and computational fluid dynamics (CFD) simulations have been applied to characterize the spray evolution and fuel-air mixing. However, most studies were focused on the spray phenomenon under a limited range of injection and ambient conditions. Especially, the prediction of spray geometry in multi-hole injectors remains a great challenge due to the lack of understanding of the complicated flow dynamics. To overcome the challenges, a series of spray experiments were carried out in a constant volume spray chamber (CVSC) coupled with high-speed Mie-scattering imaging to obtain the spray characteristics at various injection and ambient conditions. Based on the data set, the spray geometry (e.g., penetration, cone angle, spray tip velocity, area), shot-to-shot probability, and plume-to-plume variation were estimated. Furthermore, the artificial neural network (ANN) is introduced to predict the key parameters of the spray geometry to avoid the prediction errors of the existing mathematical models, and the optimal model is determined to facilitate future prediction of the spray geometry of the fuel based on the data set for algorithm training. The quantitative validation results showed that the ANN model is capable of predicting spray performance with acceptable accuracy.
Ignition and Combustion Characteristics of OME
3-5
and N-Dodecane: A Comparison Based on CFD Engine Simulations and Optical Experiments
Authors: Wiesmann Frederik , Bauer Esra , Kaiser Sebastian A. , Lauer Thomas
Published: April 2023

Synthetic fuels derived from renewable power sources, so-called e-fuels, will play a crucial role in achieving climate-neutral future mobility because they can be used in the existing fleets and in hard-to-decarbonize applications. In particular e-fuels that contain oxygen in their chemical structure can also burn more cleanly in terms of soot formation. For compression-ignition engines, polyoxymethylene dimethyl ethers (PODEs or OMEs) are among the most promising candidates for such oxygenated e-fuels.

Here, we investigated the characteristics of injection and combustion of OME3-5 mixture compared to n-dodecane, a reference diesel-like fuel. Both single and multi-injection, comprising a short pilot injection, is used. Experiments were performed in a single-cylinder optically accessible Bowditch-type engine, injecting with 1500 bar pressure with a 3-hole injector (Spray B of the Engine Combustion Network). Liquid and vapor penetration were measured by imaging the spray illuminated by a pulsed light-emitting diode (LED). Ignition delay, lift-off length and flame morphology were investigated based on multi-spectral high-speed imaging of chemiluminescence. For simulations, a 3D CFD engine model was developed. The combustion simulation was performed on a 120° sector mesh onto which flow and turbulence fields from a gas exchange simulation are mapped prior to fuel injection. The model accounts for piston-ring blow-by. For the combustion of both fuels, detailed reaction mechanisms were used. In general, quite good agreement between model predictions and experimental results was achieved. In particular the consideration of blow-by losses by the CFD model produced a realistic behavior during the high-pressure cycle.

Both CFD simulation and optical experiments, reveal significant differences between the two fuels. For OME, the liquid phase penetrates further into the combustion chamber, the ignition delay is shorter compared to n-dodecane and the equivalence ratio of OME during combustion is significantly leaner.
Injector Design and Fuel Pressure Variation for Oxygenated Spark Ignition Fuels
Authors: Kraus Christoph , Fellner Felix , Miyamoto Akiyasu , Sauerland Henning , Härtl Martin , Jaensch Malte
Published: April 2023

This study provides an overview of injector design adaptations and fuel pressure variations for oxygenated synthetic fuels, benchmarked against gasoline. The promising oxygenated fuels exhibited reduced emissions, especially with respect to particles. In gasoline engines, high fuel pressures are needed to keep the particle emissions below the permitted level. In oxygenated fuels, high fuel pressures are required to compensate for the lower volumetric energy density when used with non-adapted injectors. This study demonstrates that an adapted injector design enables engine operation with a fuel pressure reduction from 35 MPa to 10 MPa, without emission drawbacks.

The fuel investigated contained dimethyl carbonate (DMC) and methyl formate (MeFo). The fuel mass contained around 50% oxygen. A relatively high percentage of 35 vol.% MeFo was chosen because of its high vapor pressure, thus providing fast mixture formation and enabling very late compression stroke injections. The basic design adaptations are expected to be transferable to other oxygenated synthetic fuels, e.g., containing methanol (MeOH) and MeFo.

The main tests were conducted on a single cylinder research engine, based on a four-cylinder automotive engine. The exhaust gas composition was measured using an FTIR equipped with a fuel-tailored evaluation method, several standard exhaust gas analyzers, and a solid particle counting system with 10 and 23 nm cut-off sizes. The spray from both the two synthetic fuel injectors and the standard injector was further investigated at a spray chamber by means of a high-speed camera. Given a standard injector the spray pattern of 65vol% DMC+ 35vol%MeFo, and 85vol%MeOH+15 vol% MeFo were compared to the pattern of G100. All of the injectors were further investigated at an injection rate analyzer in order to provide necessary information about the injected fuel mass.