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Alternative fuels, such as natural and bio-gas, are attractive options for reducing greenhouse gas emissions from combustion engines. However, the naturally occurring variation in gas composition poses a challenge and may significantly impact engine performance. The gas composition affects fundamental fuel properties such as flame propagation speed and heat release rate. Deviations from the gas composition for which the engine was calibrated result in changes in the combustion phase, reducing engine efficiency and increasing fuel consumption and emissions. However, the efficiency loss can be limited by estimating the combustion phase and adapting the spark timing, which could be implemented favorably using a closed-loop control approach. In this paper, we evaluate the efficiency loss resulting from varying gas compositions and the benefits of using a closed-loop controller to adapt the spark timing to retain the nominal combustion phase.

The increasing need to reduce greenhouse gas emissions and shift away from fossil fuels has raised an interest for methanol. Methanol can be produced from renewable sources and can drastically lower soot emissions from compression ignition engines (CI). As a result, research and development efforts have intensified focusing on the use of methanol as a replacement for diesel in CI engines. The issue with methanol lies in the fact that methanol is challenging to ignite through compression alone, particularly at low-load and cold starts conditions. This challenge arises from methanol's high octane number, low heating value, and high heat of vaporization, all of which collectively demand a substantial amount of heat for methanol to ignite through compression.

The growing demand to lower greenhouse gas emissions and transition from fossil fuels, has put methanol in the spotlight. Methanol can be produced from renewable sources and has the property of burning almost soot-free in compression ignition (CI) engines. Consequently, there has been a notable increase in research and development activities directed towards exploring methanol as a viable substitute for diesel fuel in CI engines. The challenge with methanol lies in the fact that it is difficult to ignite through compression alone, particularly in low-load and cold start conditions. This difficulty arises from methanol's high octane number, relatively low heating value, and high heat of vaporization, collectively demanding a considerable amount of heat for methanol to ignite through compression. Previous studies have addressed the use of a pilot injection in conjunction with a larger main injection to lower the required intake air temperature for methanol to combust at low loads.

Methanol has recently emerged as a promising fuel for internal combustion engines due to its multiple carbon-neutral production routes and advantageous properties when combusting. Methanol is intrinsically more suitable for spark-ignition (SI) operation thanks to its high octane number, but its potential in heavy-duty applications also encourages engine manufacturers in this field to retrofit their existing compression-ignition products into methanol/diesel dual-fuel (DF) operation. For both SI operation and DF operation, injecting methanol into the engine’s intake path at low pressure is a relatively simple and robust method to introduce methanol into the cylinders. However, the much higher heat of vaporization (HoV) of methanol compared to conventional SI fuels like gasoline can be a double-edged sword.

In the upcoming decade sustainable powertrain technologies will seek for market entrance in the transport sector. One promising solution is the utilization of dual-fuel engines using renewable methanol ignited by a pilot diesel fuel. This approach allows the displacement of a significant portion of fossil diesel, thereby reducing greenhouse gas emissions. Additionally, this technology is, next to newbuilds, suited for retrofitting existing engines, while maintaining high efficiencies and lowering engine-out emissions. Various researchers have experimentally tested the effects of replacing diesel by methanol and have reported different boundaries for substituting diesel by methanol, including misfire, partial burn, knock and pre-ignition. However, little research has been conducted to explore ways to extend these substitution limits.

The use of renewable fuels such as hydrogen and methanol in marine engines is a promising way to reduce greenhouse gas emissions from maritime transport. Hydrogen and methanol can be used as the main fuel in dual-fuel engines. However, the co-combustion of hydrogen-diesel and methanol-diesel needs to be carefully studied. In the present work, the ignition delay (ID) and laminar burning velocity (LBV) for pilot-ignited dual fuel engine operation with hydrogen or methanol are studied. A constant volume batch reactor numerical setup is used in the open source Cantera code to calculate the effect of the premixed fuel on the ID of the pilot fuel. Also, Cantera is used to simulate a freely-propagating, adiabatic, 1-D flame to estimate the laminar flame speed of either hydrogen or methanol and how it is affected by the presence of pilot fuel. First, suitable chemical kinetic schemes are selected based on experimental data collected from the literature.

Using renewable fuels is a reliable approach for decarbonization of combustion engines. iso-Butanol and n-butanol are known as longer chain alcohols and have the potential of being used as gasoline substitute or a renewable fraction of gasoline. The combustion behavior of renewable fuels in modern combustion engines and advanced combustion concepts is not well understood yet. Low-temperature combustion (LTC) is a concept that is a basis for some of the low emissions-high efficiency combustion technologies. Fuel ɸ-sensitivity is known as a key factor to be considered for tailoring fuels for these engines. The Lund ɸ-sensitivity method is an empirical test method for evaluation of the ɸ-sensitivity of liquid fuels and evaluate fuel behavior in thermal. iso-Butanol and n-butanol are two alcohols which like other alcohol exhibit nonlinear behavior when blended with (surrogate) gasoline in terms of RON and MON.

The worldwide adoption of renewable energy mandates, together with the widespread utilization of biofuels has created a sharp increase in the production of biodiesel (fatty acid alkyl esters). As a consequence, the production of glycerol, the main by-product of the transesterification of fatty acids, has increased accordingly, which has led to an oversupply of that compound on the markets. Therefore, in order to increase the sustainability of the biodiesel industry, alternative uses for glycerol need to be explored and the production of fuel additives is a good example of the so-called glycerol valorization. The goal of this study is therefore to evaluate the suitability of a number of glycerol-derived compounds as diesel fuel additives. Moreover, this work concerns the assessment of low-concentration blends of those glycerol derivatives with diesel fuel, which are more likely to conform to the existing fuel standards and be used in unmodified engines.

Non-Road Mobile Machinery (NRMM) incorporates a wide variety of machines not intended for the transport of passengers or goods on the road. This includes small gardening equipment, construction, mining, agricultural, and forestry machinery up to locomotives and inland waterway vessels, mostly using an internal combustion engine. NRMM was often overlooked and neglected in the past when considering pollutant and greenhouse gas emissions. Due to their high diversity, they are hard to categorize, resulting in a lack of available data. As emissions from road transport are being tackled by regulations, the emissions of NRMM become an increasing part of total transport emissions. An alternative to fossil fuels will be required for the energy supply of NRMM to fully commit to the CO2 reduction goals, and to fulfil the future requirements of legislators and public opinion.

This study explores the potential benefits of combining a wave-shaped piston geometry with post injection strategy in diesel engines. The wave piston design features evenly spaced protrusions around the piston bowl, which improve fuel-air mixing and combustion efficiency. The 'waves' direct the flames towards the bowl center, recirculating them and utilizing the momentum in the flame jets for more complete combustion. Post injection strategy, which involves a short injection after the main injection, is commonly used to reduce emissions and improve fuel efficiency. By combining post injections with the wave piston design, additional fuel injection can increase the momentum utilized by the flame jets, potentially further improving combustion efficiency. To understand the effects and potential of the wave piston design with post injection strategy, a single-cylinder heavy-duty compression-ignition optical engine with a quartz piston is used.

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.

In the search for sustainable transportation fuels that are not in competition with food production, considerable efforts are made in the development of so-called second-generation (2G) biofuels. This paper looks into the results of a novel 2G biofuel production technique that is based on a catalytic process that operates at low temperature and that converts woody biomass feedstock into a stable light naphtha. The process development is integrated in the Belgian federal government funded Ad-Libio project and the process outcome is mainly consisting of hydrocarbons containing five to six carbon atoms. Their composition can be altered, resulting in a large amount of different possible fuel blends. The ultimate goal is to produce a drop-in fuel that can be fully interchanged with the gasoline fuels in use today. This is a challenge, since the Ad-Libio fuel components differ significantly from gasoline fuel components.

Despite the increasing number of electrified vehicles the transportation system still largely depends on the use of fossil fuels. One way to more rapidly reduce the dependency on fossil fuels in transport is to replace them with biofuels. Evaluating the potential of different biofuels in different applications requires knowledge of their physicochemical properties. In chemistry, message passing neural networks (MPNNs) correlating the atoms and bonds of a molecule to properties have shown promising results in predicting the properties of individual chemical components. In this article a machine learning approach, developed from the message passing neural network called Chemprop, is evaluated for the prediction of multiple properties of organic molecules (containing carbon, nitrogen, oxygen and hydrogen). A novel approach using transfer learning based on estimated property values from theoretical estimation methods is applied.

A modern diesel engine is a reliable and efficient mean of producing power. A way to reduce harmful exhaust and greenhouse gas (GHG) emissions and secure the sources of energy is to develop technology for an efficient diesel engine operation independent of fossil fuels. Renewable diesel fuels are compatible with diesel engines without any major modifications. Rapeseed oil methyl esters (RME) and other fatty acid methyl esters (FAME) are commonly used in low level blends with diesel. Lately, hydrotreated vegetable oil (HVO) produced from vegetable oil and waste fat has found its way into the automotive market, being approved for use in diesel engines by several leading vehicle manufacturers, either in its pure form or in a mixture with the fossil diesel to improve the overall environmental footprint. There is a lack of data on how renewable fuels change the semi-volatile organic fraction of exhaust emissions.

Increasingly stringent pollutant and CO2 emission standards require the car manufacturers to investigate innovative solutions to further improve the fuel economy and environmental impact of their fleets. Nowadays, NOx emissions standards are stringent for spark-ignition (SI) internal combustion engines (ICEs) and many techniques are investigated to limit these emissions. Among these, an extremely lean combustion has a large potential to simultaneously reduce the NOx raw emissions and the fuel consumption of SI ICEs. Engines with pre-chamber ignition system are promising solutions for realizing a high air-fuel ratio which is both ignitable and with an adequate combustion speed. In this work, the combustion characteristics of an active pre-chamber system are experimentally investigated using a single-cylinder research engine. The engine under exam is a large bore heavy-duty unit with an active pre-chamber fuelled with compressed natural gas.

An increasing need to lower greenhouse gas emissions, and so move away from fossil fuels like diesel and gasoline, has greatly increased the interest for methanol. Methanol can be produced from renewable sources and eliminate soot emissions from combustion engines [1]. Since compression ignition (CI) engines are used for the majority of commercial applications, research is intensifying into the use of methanol, as a replacement for diesel fuel, in CI engines. This includes work on dual-fuel set-ups, different fuel blends with methanol, ignition enhancers mixed with methanol, and partially premixed combustion (PPC) strategies with methanol. However, methanol is difficult to ignite, using compression alone, at low load conditions. The problem comes from methanol’s high octane number, low lower heating value and high heat of vaporization, which add up to a lot of heat being needed from the start to combust methanol [2].

A commercially available fuel, E85, a blend of ~85% ethanol and ~15% gasoline, can be a viable substitute for fossil fuels in internal combustion engines in order to achieve a reduction of the greenhouse gas (GHG) emissions. Ethanol is traditionally made of biomass, which makes it a part of the food-feed-fuel competition. New processes that reuse waste products from other industries have recently been developed, making ethanol a renewable and sustainable second-generation fuel. So far, work on E85 has focused on spark ignition (SI) concepts due to high octane rating of this fuel. There is very little research on its application in CI engines. Alcohols are known for low soot particle emissions, which gives them an advantage in the NOx-soot trade-off of the compression ignition (CI) concept.

In order to reduce the carbon footprint of the Internal Combustion Engine (ICE), biofuels have been in use for a number of years. One of the problems with first-generation (1G) biofuels however is their competition with food production. In search of second-generation (2G) biofuels, that are not in competition with food agriculture, a novel biorefinery process has been developed to produce biofuel from woody biomass sources. This novel technique, part of the Belgian federal government funded Ad-Libio project, uses a catalytic process that operates at low temperature and is able to convert 2G feedstock into a stable light naphtha. The bulk of the yield consists out of hydrocarbons containing five to six carbon atoms, along with a fraction of oxygenates and aromatics. The oxygen content and the aromaticity of the hydrocarbons can be varied, both of which have a significant influence on the fuel’s combustion and emission characteristics when used in Internal Combustion Engines.

To speed up the development of the next-generation combustion engines with renewable fuels, the importance of reliable and robust simulations cannot be overemphasized. Compared to gasoline, methanol is a promising fuel for spark-ignited engines due to its higher research octane number to resist auto-ignition, higher flame speed for faster combustion and higher heat of vaporization for intake charge cooling. These advantageous properties all contribute to higher thermal efficiency and lower knock tendency, and they need to be well-captured in the simulation environment in order to generate accurate predictions. In this paper, the sub-models which estimate the burning velocities and ignition delay of methanol are revisited. These building blocks are implemented and integrated in a quasi-dimensional simulation environment to predict the combustion behavior, which are subsequently validated against test data measured on both light-duty and heavy-duty engines.

Active prechamber combustion systems for SI engines represent a feasible and effective solution in reducing fuel consumption and pollutant emissions for both marine and ground heavy-duty engines. However, reliable and low-cost numerical approaches need to be developed to support and speed-up their industrial design considering their geometry complexity and the involved multiple flow length scales. This work presents a CFD methodology based on the RANS approach for the simulation of active prechamber spark-ignition engines. To reduce the computational time, the gas exchange process is computed only in the prechamber region to correctly describe the flow and mixture distributions, while the whole cylinder geometry is considered only for the power-cycle (compression, combustion and expansion). Outside the prechamber the in-cylinder flow field at IVC is estimated from the measured swirl ratio.