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Technical Paper

Sustainable Fuels for Long-Haul Truck Engines: A 1D-CFD Analysis

2024-06-12
2024-37-0027
Heavy duty engines for long-haul trucks are quite difficult to electrify, due to the large amount of energy that should be stored on-board to achieve a range comparable to that of conventional fuels. In particular, this paper considers a stock engine with a displacement of 12.9 L, developed by the manufacturer in two different versions. As a standard diesel, the engine is able to deliver about 420 kW at 1800 rpm, whereas in the compressed natural gas configuration the maximum power output is 330 kW, at the same speed. Three possible alternatives to these fossil fuels are considered in this study: biodiesel (HVOlution by Eni), bio-methane and green hydrogen. While the replacement of diesel and compressed natura gas with biofuels does not need significant hardware modifications, the implementation of a hydrogen spark ignition combustion system requires a deep revision of the engine concept.
Technical Paper

The Evolution of Conventional Vehicles’ Efficiency for Meeting Carbon Neutrality Ambition

2024-06-12
2024-37-0034
In 2023, the European Union set more ambitious targets for reducing greenhouse gas emissions from passenger cars: the new fleet-wide average targets became 93.6 g/km for 2025, 49.5 g/km in 2030, going to 0 in 2035. One year away from the 2025 target, this study evaluates what contribution to CO2 reduction was achieved from new conventional vehicles and how to interpret forecasts for future efficiency gains. The European Commission’s vehicle efficiency cost-curves suggest that optimal technology adoption can guarantee up to 50% CO2 reduction by 2025 for conventional vehicles. Official registration data between 2013 and 2022, however, reveal only an average 14% increase in fuel efficiency in standard combustion vehicles, although reaching almost 23% for standard hybrids. The smallest gap between certified emissions and best-case scenarios is of 14 g/km, suggesting that some manufacturers’ declared values are approaching the optimum.
Technical Paper

Guided Port Injection of Hydrogen as an Approach for Reducing Cylinder-to-Cylinder Deviations in Spark-Ignited H2 Engines – A Numerical Investigation

2024-06-12
2024-37-0008
The reduction of anthropogenic greenhouse gas emissions and ever stricter regulations on pollutant emissions in the transport sector require research and development of new, climate-friendly propulsion concepts. The use of renewable hydrogen as a fuel for internal combustion engines promises to provide a good solution especially for commercial vehicles. For optimum efficiency of the combustion process, hydrogen-specific engine components are required, which need to be tested on the test bench and analysed in simulation studies. This paper deals with the simulation-based investigation and optimisation of fuel injection in a 6-cylinder PFI commercial vehicle engine, which has been modified for hydrogen operation starting from a natural gas engine concept.
Technical Paper

Effects of Renewable Fuels on the Performance and Emissions of a Small Displacement Diesel Engine for Urban Mobility

2024-06-12
2024-37-0019
In the frame of growing concerns over climate change and health, renewable fuels can make an important contribution to decarbonizing the transport sector. The current work presents the results of an investigation into the impact of renewable fuels on the combustion and emissions of a turbocharged compression-ignition internal combustion engine. An experimental study was undertaken and the engine settings were not modified to account for the fuel's chemical and physical properties, to analyze the performance of the fuel as a potential drop-in alternative fuel. Three fuels were tested: mineral diesel, a blend of it with waste cooking oil biodiesel and a hydrogenated diesel. The analysis of the emissions at engine exhaust highlights that hydrogenated fuel is cleaner, reducing CO, total hydrocarbon emissions, particulate matter and NOx.
Technical Paper

Experimental Study of Lignin Fuels for CI Engines

2024-06-12
2024-37-0022
This study explores the feasibility of using a sustainable lignin-based fuel, consisting of 44 % lignin, 50 % ethanol, and 6 % water, in conventional compression ignition (CI) marine engines. Through experimental evaluations on a modified small-bore CI engine, we identified the primary challenges associated with lignin-based fuel, including engine startup and shutdown issues due to solvent evaporation and lignin solidification inside the fuel system, and deposit formation on cylinder walls leading to piston ring seizure. To address these issues, we developed a fuel switching system transitioning from lignin-based fuel to cleaning fuel with 85 vol% of acetone, 10 vol% of water and 5 vol% of ignition improving additive, effectively preventing system clogs.
Technical Paper

Influence of Intake Charge Temperature and EGR Rate on the Combustion and Emission Characteristics of Ammonia/Diesel Dual-Fuel Engine

2024-06-12
2024-37-0025
Ammonia has emerged as a promising carbon-free alternative fuel for internal combustion engines (ICE), particularly in large-bore engine applications. However, integrating ammonia into conventional engines presents challenges, prompting the exploration of innovative combustion strategies like dual-fuel combustion. Nitrous oxide (N2O) emissions have emerged as a significant obstacle to the widespread adoption of ammonia in ICE. Various studies suggest that combining exhaust gas recirculation (EGR) with adjustments in inlet temperature and diesel injection timing can effectively mitigate nitrogen oxides (NOx) emissions across diverse operating conditions in dual-fuel diesel engines.
Journal Article

Effects of Dimethyl Ether and Propane Blends on Knocking Behavior in a Boosted SI Engine

2024-06-12
Abstract Dimethyl ether (DME) is an alternative fuel that, blended with propane, could be an excellent alternative for exploring the use of fuels from renewable sources. DME–propane blends are feasible for their comparable physicochemical properties; these fuels may be pressured as liquids using moderate pressure at ambient temperature. Adding a proportion of DME with a low octane number to a less reactive fuel like propane can improve the combustion process. However, the increased reactivity of the mixture induced by the DME could lead to the early appearance of knocking, and this tendency may even be pronounced in boosted SI engines.
Journal Article

Numerical Investigation of Combustion Characteristics in a Binary Fuel Blend of C8H18 and H2

2024-06-10
Abstract The escalating energy demand in today’s world has amplified exhaust emissions, contributing significantly to climate change. One viable solution to mitigate carbon dioxide emissions is the utilization of hydrogen alongside gasoline in internal combustion engines. In pursuit of this objective, combustion characteristics of iso-octane/hydrogen/air mixtures are numerically investigated to determine the impact of hydrogen enrichment. Simulations are conducted at 400 K over a wide range of equivalence ratio 0.7 ≤ Ф ≤ 1.4 and pressure 1–10 atm. Adiabatic flame temperature, thermal diffusivity, laminar burning velocity, and chemical participation are assessed by varying hydrogen concentration from 0 to 90% of fuel molar fraction. As a result of changes in thermal properties and chemical participation, it is noticed that the laminar burning velocity (LBV) increases with higher hydrogen concentration and decreases as pressure increases.
Journal Article

Effect of Injector Type and Intake Boosting on Combustion, Performance, and Emission Characteristics of a Spray-Guided Gasoline Direct Injection Engine—A Computational Fluid Dynamics Study

2024-06-06
Abstract In general, GDI engines operate with stratified mixtures at part-load conditions enabling increased fuel economy with high power output, however, with a compensation of increased soot emissions at part-load conditions. This is mainly due to improper in-cylinder mixing of air and fuel leading to a sharp decrease in gradient of reactant destruction term and heat release rate (HRR), resulting in flame quenching. The type of fuel injector and engine operating conditions play a significant role in the in-cylinder mixture formation. Therefore, in this study, a CFD analysis is utilized to compare the effect of stratified mixture combustion with multi-hole solid-cone and hollow-cone injectors on the performance and emission characteristics of a spray-guided GDI engine. The equivalence ratio (ϕ) from 0.6 to 0.8 with the constant engine speed of 2000 rev/min is considered. For both injectors, the fuel injection pressure of 200 bar is used with 60° spray-cone angles.
Technical Paper

Influences of High-Pressure Pump and Injector Nozzle Geometry on Hydraulics Characteristics of a Mechanical Diesel Direct-Injection System

2024-06-04
2024-01-5061
The geometry of high-pressure pump and injector nozzles crucially influences hydraulic behaviors (e.g., the start of injection, the pressure profiles developed in the high-pressure line, needle lift, and injection rates) in diesel engines. These factors, in turn, significantly impact fuel atomization, fuel–air mixing, combustion quality, and the formation of emissions. The main geometry parameters such as plunger diameter and the number and diameter of nozzles lead to the system complexity, requiring careful analysis, design, and calibration. In this study, a high-speed shadowgraph system and a high-resolution pressure recording system were developed to capture the start of injection, spray structure, and pressure profiles in the high-pressure line. Additionally, a model was developed using GT-Fuel package built within the GT-Suite of simulation tools to explore different plunger diameters and numbers and diameters of injector nozzles.
Journal Article

The Hybrid Concept of Turboshaft Engine Enhanced by Steam Cycle Using Waste Heat Recovery—Combined Analytical and Numerical Calculation of Its Efficiency

2024-06-04
Abstract The article presents a hybrid concept of a turboshaft engine that fits into the area of PGE (pressure-gained combustion). It combines the advantages and elements of a piston engine and a turbine engine. The combustion takes place in isochoric chambers. The proposed timing system of the engine efficiently realizes the Humphrey cycle. Additionally, the main gas cycle engine was enhanced by the Clausius–Rankine steam cycle to achieve effective power of engine equal to 1231.3 kW. It was supplied by waste heat recovery from the exhaust gas. The enhancement of the engine by the secondary steam cycle significantly improved engine effective efficiency with a final value reaching 0.446. The effective efficiency and specific fuel consumption of the engine were calculated using merged analytical–numerical CFD (computational fluid dynamics) analysis. The centrifugal compressor, gas turbine, and steam turbine can work on the common shaft whose rotational velocity is 35,000 rpm.
Journal Article

Auto-Ignited Combustion Control in an Engine Equipped with Multiple Boosting Devices

2024-06-03
Abstract The combustion timing of auto-ignited combustion is determined by composition, temperature, and pressure of cylinder charge. Thus, for a successful auto-ignition, those key variables must be controlled within tight target ranges, which is challenging due to (i) nature of coupling between those variables, and (ii) complexity of managing multiple actuators in the engine. In this article, a control strategy that manages multiple actuators of a boosted homogeneous charge compression ignition (HCCI) engine is developed to maintain robust auto-ignited combustion. The HCCI engine being considered is equipped with multiple boosting devices including a supercharger and a turbocharger in addition to conventional actuators and sensors. Since each boosting device has its own pros and cons, harmonizing those boosting devices is crucial for successful transient operation.
Technical Paper

Thermal Analysis of Prismatic Core Sandwich Structural Panel for Hypersonic Application

2024-06-01
2024-26-0422
Hypersonic flight vehicles have potential applications in strategic defence, space missions, and future civilian high-speed transportation systems. However, structural integration has significant challenges due to extreme aero-thermo-mechanical coupled effects. Scramjet-powered air-breathing hypersonic vehicles experience extreme heat loads induced by combustion, shock waves and viscous heat dissipation. An active cooling thermal protection system for scramjet applications has the highest potential for thermal load management, especially for long-duration flights, considering the weight penalty associated with the heavier passive thermal insulation structures. We consider the case of active cooling of scramjet engine structural walls with endothermic hydrocarbon fuel. We have developed a semi-analytical quasi-2D heat transfer model considering a prismatic core single cooling channel segment as a representative volume element (RVE) to analyse larger-scale problems.
Journal Article

Effect of Ethanol and Iso-Octane Blends on Isolated Low-Temperature Heat Release in a Spark Ignition Engine

2024-05-17
Abstract Low-temperature heat release (LTHR) is of interest for its potential to help control autoignition in advanced compression ignition (ACI) engines and mitigate knock in spark ignition (SI) engines. Previous studies have identified and investigated LTHR in both ACI and SI engines before the main high-temperature heat release (HTHR) event and, more recently, LTHR in isolation has been demonstrated in SI engines by appropriately curating the in-cylinder thermal state during compression and disabling the spark discharge. Ethanol is an increasingly common component of market fuel blends, owing to its renewable sources. In this work, the effect of adding ethanol to iso-octane (2,2,4-trimethylpentane) blends on their LTHR behavior is demonstrated. Tests were run on a motored single-cylinder engine elevated inlet air temperatures and pressures were adjusted to realize LTHR from blends of iso-octane and ethanol without entering the HTHR regime.
Journal Article

Unveiling the Potential of Hydrogen in a Downsized Gasoline Direct Injection Engine Performance and Emissions Experimental Study

2024-05-11
Abstract The transportation sector’s growing focus on addressing environmental and sustainable energy concerns has led to a pursuit of the decarbonization path. In this context, hydrogen emerges as a promising zero-carbon fuel. The ability of hydrogen fuel to provide reliable performance while reducing environmental impact makes it crucial in the quest for net zero targets. This study compares gasoline and hydrogen combustion in a single-cylinder boosted direct injection (DI) spark ignition engine under various operating conditions. Initially, the engine was run over a wide range of lambda values to determine the optimal operating point for hydrogen and demonstrate lean hydrogen combustion’s benefits over gasoline combustion. Furthermore, a load sweep test was conducted at 2000 rpm, and the performance and emission results were compared between gasoline and optimized hydrogen combustion. An in-depth analysis was conducted by varying fuel injection time and pressure.
Journal Article

Determination of Air–Fuel Ratio at 1 kHz via Mid-Infrared Laser Absorption and Fast Flame Ionization Detector Measurements in Engine-Out Vehicle Exhaust

2024-04-29
Abstract Measurements of air–fuel ratio (AFR) and λ (AFRactual/AFRstoich) are crucial for understanding internal combustion engine (ICE) performance. However, current λ sensors suffer from long light-off times (on the order of seconds following a cold start) and limited time resolution. In this study, a four-color mid-infrared laser absorption spectroscopy (LAS) sensor was developed to provide 5 kHz measurements of temperature, CO, CO2, and NO in engine-out exhaust. This LAS sensor was then combined with 1 kHz hydrocarbon (HC) measurements from a flame ionization detector (FID), and the Spindt exhaust gas analysis method to provide 1 kHz measurements of λ. To the authors’ knowledge, this is the first time-resolved measurement of λ during engine cold starts using the full Spindt method. Three tests with various engine AFR calibrations were conducted and analyzed: (1) 10% lean, (2) stoichiometric, and (3) 10% rich.
Journal Article

Combustion Analysis of Active Pre-Chamber Design for Ultra-Lean Engine Operation

2024-04-27
Abstract In this article, the effects of mixture dilution using EGR or excessive air on adiabatic flame temperature, laminar flame speed, and minimum ignition energy are studied to illustrate the fundamental benefits of lean combustion. An ignition system developing a new active pre-chamber (APC) design was assessed, aimed at improving the indicated thermal efficiency (ITE) of a 1.5 L four-cylinder gasoline direct injection (GDI) engine. The engine combustion process was simulated with the SAGE detailed chemistry model within the CONVERGE CFD tool, assuming the primary reference fuel (PRF) to be a volumetric mixture of 93% iso-octane and 7% n-heptane. The effects of design parameters, such as APC volume, nozzle diameter, and nozzle orientations, on ITE were studied. It was found that the ignition jet velocity from the pre-chamber to the main chamber had a significant impact on the boundary heat losses and combustion phasing.
Journal Article

Optimized Emission Analysis in Hydrogen Internal Combustion Engines: Fourier Transform Infrared Spectroscopy Innovations and Exhaust Humidity Analysis

2024-04-23
Abstract In today’s landscape, environmental protection and nature conservation have become paramount across industries, spurring the ever-increasing aspect of decarbonization. Regulatory measures in transportation have shifted focus away from combustion engines, making way for electric mobility, particularly in smaller engines. However, larger applications like ships and stationary power generation face limitations, not enabling an analogous shift to electrification. Instead, the emphasis shifted to zero-carbon fuel alternatives such as hydrogen and ammonia. In addition to minimal carbon-containing emissions due to incineration of lubricating oil, hydrogen combustion with air results in nitrogen oxide emissions, still necessitating quantification for engine operation compliance with legal regulations.
Journal Article

Dimethyl Ether Biogas Reactivity-Controlled Compression Ignition for Sustainable Power Generation with Low Nitrogen Oxide Emissions

2024-04-22
Abstract Biogas (60% methane–40% CO2 approximately) can be used in the reactivity-controlled compression ignition (RCCI) mode along with a high-reactivity fuel (HRF). In this work dimethyl ether (DME) that can also be produced from renewable sources was used as the HRF as a move toward sustainable power generation. The two-cylinder turbocharged diesel engine modified to work in the DME–biogas RCCI (DMB-RCCI) mode was studied under different proportions of methane (45–95%) in biogas since the quality of this fuel can vary depending on the feedstock and production method. Only a narrow range of biogas to DME ratios could be tolerated in this mode at each output without misfire or knock. Detailed experiments were conducted at brake mean effective pressures (BMEPs) of 3 and 5 bar at a speed of 1500 rpm and comparisons were made with the diesel–biogas dual-fuel and diesel–biogas RCCI modes under similar methane flow rates while the proportion of CO2 was varied.
Journal Article

Hydrogen Injection Position Impact: Experimental Analysis of Central Direct Injection and Side Direct Injection in Engines

2024-04-18
Abstract A detailed investigation was carried out on the performance, combustion, and emissions of a single-cylinder direct injection hydrogen spark ignition (SI) engine with either a side-mounted direct injection (SDI) or a centrally installed direct injection (CDI) injector. The first part of the study analyzed the performance and emissions characteristics of CDI and SDI engine operations with different injection timings and pressures. This was followed by comparing the engine’s performance and emissions of the CDI and SDI operations at different engine speeds and relative air-to-fuel ratios (lambda) with the optimized injection pressure and timings. Furthermore, the performance and emission attributes of the hydrogen engine with the CDI and SDI setups were conducted at a fixed λ value of 2.75 across a broad spectrum of engine loads. The study’s main outcome demonstrates that both direct injection systems produced near-zero CO2, CO, and HC emissions.
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