André L. Boehman

This study presents a fuel-flexible quasi-dimensional Spark Ignition (SI) engine combustion model for predicting the burn rate and knock in gasoline-syngas blends. The framework utilizes a multizone structure and a dedicated knock combustion model, while introducing two key advancements for fuel flexibility of the entire engine model: (i) a novel machine-learning-based laminar flame speed model that captures the nonlinear dependence of the turbulent burn rate on fuel composition and thermodynamic properties, and (ii) an extended ignition delay model that incorporates syngas (H 2 /CO) components for knock prediction. In this study, gasoline is represented by an optimized toluene reference fuel (TRF) surrogate along with H 2 and CO to enable simulation of gasoline-syngas blends. The model is calibrated and validated against single-cylinder SI engine experiments at 1500 rpm and 0.8–1.0 bar of intake pressures. The new SI engine model accurately reproduces in-cylinder pressure traces, apparent heat release rates, combustion phasing (CA05–CA90 deviations <2 °CA), indicated mean effective pressure (<2.5%), inducted mass flow (<2.5%), and knock-limited spark timing (<1 °CA), mostly within the experimental cycle-to-cycle variability. Crucially, the model successfully predicts the change in the detonation borderline resulting from syngas addition, demonstrating its ability to resolve the competing effects of a faster burn rate and a longer ignition delay time with satisfactory accuracy. Overall, this modular and composition-sensitive framework provides a scalable platform for predictive combustion and knock modeling of multifuel options in SI engines.

The carbon footprint and particulate matter emissions of diesel engines may be reduced by replacing conventional diesel fuel with ethanol. However, ethanol has a poor tendency for autoignition, and is therefore difficult to use with conventional diesel combustion strategies. In this study, exhaust rebreathing is used to increase cylinder temperatures and enable mixing-controlled compression ignition of ethanol in experiments on a heavy-duty diesel engine. The exhaust rebreathing strategy is also implemented with conventional diesel fuel. Results with each fuel are compared to results with conventional diesel fuel using a production-like calibration at a medium torque condition. Finally, the same exhaust rebreathing valve strategy is applied to extremely low load operation with ethanol to investigate the feasible limit of exhaust rebreathing operation. Diesel-like engine performance was achieved with ethanol at medium torque. Analysis of apparent heat release rates revealed that ethanol ignition delay was sensitive to backpressure, whereas diesel fuel ignition delay changed very little across a similar backpressure sweep. As compared to a production-like diesel baseline, the exhaust rebreathing strategy with ethanol penalized thermal efficiency and NOx emissions slightly, but improved particulate and CO emissions. At 1 bar IMEP, coefficient of variation of IMEP as low as 5% was achieved with ethanol, indicating that stable, diesel-like combustion could be achieved at even the lowest loads via exhaust rebreathing. The results of this study demonstrate the feasibility of operating a heavy-duty diesel engine on ethanol, diesel fuel, or any mixture of the two using an exhaust rebreathing strategy.

Higher alcohols are attractive sustainable blendstocks for diesel fuel as they may be produced through biological processes or the upgrade of abundant bioethanol. To use alcohols as blendstocks for diesel fuel, the properties of the resulting blends must comply with the standard specifications for diesel fuel. By understanding the effects of alcohol molecular structure on relevant fuel properties, processes producing higher alcohols can be designed to elicit the desired structure. In this study, blends of five pure higher alcohols (1-butanol, 1-hexanol, 1-octanol, 2-ethyl-1-butanol, and 2-ethyl-1-hexanol) with conventional diesel fuel were characterized to evaluate the effects of both carbon number and branching on the suitability of alcohols as a diesel fuel blendstock. In addition to properties regulated by ASTM D975, combustion performance was also studied through the analysis of the spray autoignition process and sooting tendency. Unbranched alcohols of higher molecular weight better preserved the flash point, lubricity, and derived cetane number when blended with diesel fuel. Blending 1-butanol into diesel fuel at any volume fraction resulted in a flash point less than 40 °C. All other alcohols considered in this study remained in compliance with ASTM D975 at a 20% blending volume fraction. None of the alcohols significantly compromised the cloud point, but pure 1-octanol had a cloud point about 10 °C greater than diesel fuel. While branched isomers resulted in lower cetane numbers than normal alcohols, isomerization preserved the cold flow performance for heavy alcohol blendstocks. It was also found that the sooting tendency was uniformly reduced by normal alcohol blending, independent of alcohol molecular weight. Blends with branched alcohols resulted in a 25% smaller reduction in the sooting tendency compared to normal isomers. These results can inform the design of higher-alcohol-based blendstocks for diesel fuel across a variety of applications.

Pyrolysis is a promising thermochemical process for managing sewage sludge while simultaneously producing biochar, a valuable co-product. This study systematically investigated the effects of the pyrolysis parameters of temperature (200–800 °C), residence time (5–60 min), and inert gas flow rate (0.25–1.0 dm 3 /min) on the properties of biochars obtained from sewage sludge. Comprehensive characterization of the biochars was conducted, including composition analyses (ultimate, proximate, elemental, and molecular), acidity, specific surface area and pore size, and the assessment of eight heavy metals (As, Cd, Pb, Cr, Zn, Mn, Ni and Cu) in the biochars and sewage sludge. The results showed pyrolysis temperature and residence time were the most critical parameters affecting biochar quality, with negligible influence of inert gas flow rate. Higher pyrolysis temperatures ( > 500 °C) increased biochar pH to alkaline values ( > 10), ash content, and nutrient concentrations (Ca, K, Mg, P). Temperatures above 600 °C significantly increased biochar surface area, reduced pore size, and yielded H/C ratios below 0.57, improving suitability for soil remediation. Pyrolysis also facilitated volatilization of heavy metals, particularly As and Cd, which were reduced to safe levels, with Cd removal exceeding 90% at 700 °C. Metal analysis confirmed the immobilization of heavy metals in biochar, significantly reducing the environmental risk, from high (PERI = 1158) in the sewage sludge feedstock to low (PERI < 50) in biochar obtained at temperatures above 600 °C. Most heavy metals in biochar at these temperatures were concentrated in oxidizable and residual fractions. The results provide valuable new data to guide development of pyrolysis for the sustainable management of sewage sludge.

&lt;div&gt;In this study, a strategy for MCCI combustion of a novel alcohol fuel is demonstrated. The novel fuel, “GrenOl”, is the result of the catalytic upgrade of sustainable ethanol into alcohols of higher molecular weight. The composition of GrenOl includes approximately 70% 1-butanol, 15% 1-hexanol, and 5% 1-octanol by mass, resulting in a cetane number around 18.&lt;/div&gt; &lt;div&gt;In order to achieve mixing-controlled compression ignition with GrenOl, an exhaust rebreathing strategy is employed. In this strategy, the exhaust valve reopens for a part of the intake stroke, inducting hot exhaust into the cylinder and preheating the fresh air. This study investigates the feasibility of operating with such a valve strategy from idle to peak torque. At idle, the primary challenge is ensuring stable combustion by inducting adequate exhaust to achieve ignition. Under load, when cylinder temperatures are higher, the primary challenge is ensuring sufficient air is inducted to achieve the target torque.&lt;/div&gt; &lt;div&gt;It was found that a modest exhaust rebreathing valve strategy could ensure stable combustion with diesel-like emissions and efficiency from idle to peak torque. Coefficient of variation of IMEP as low as 2% was achieved at idle, matching diesel idle stability despite the very low cetane number of the fuel. At medium load, indicated specific fuel consumption was as low as 235 g/kWh, and engine-out indicated specific NOx emissions were as low as 4 g/kWh. Peak torque was attained despite the volumetric efficiency penalty imposed by exhaust rebreathing.&lt;/div&gt; &lt;div&gt;These results demonstrate the feasibility of operating a diesel engine on neat, sustainable, ethanol-derived fuel over the entire engine operating map with minimal well-defined design modifications. Future work should extend these findings to multicylinder engines and challenging cold start conditions.&lt;/div&gt;

The U.S. Department of Energy Supertruck 2 program placed emphasis on development of heavy-duty trucks with high freight efficiency using commercially realizable technology suites. This paper describes the research and development process used to pursue a high thermal efficiency heavy-duty engine under Supertruck 2 . The team focused on over-expanded engine cycles and advanced piston designs. This paper describes how single-cylinder engine studies using thermal barrier coated pistons, high compression pistons, and over-expanded cycles informed the development process of a multi-cylinder demonstration engine that achieved 49.9% peak thermal efficiency. While tailoring the injection strategy and other control parameters optimized the demonstration engine, more than half of the efficiency improvement came from the over-expanded cycle.

&lt;div&gt;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. Hence, this study experimentally analyzes the effect of E10 gasoline (baseline) and DME–propane blends, with varying proportions of DME in propane ranging from 0% to 30% by weight, in increments of 5% on knocking tendency, combustion characteristics, gaseous emissions, and particle number concentration, under different intake pressure conditions (0.8, 0.9, 1.0, and 1.1 bar) in an SI engine. The results show that as the proportion of DME in the propane blend rises, the knocking tendency becomes more pronounced. That behavior intensifies with increasing intake pressure, but with 20% DME in the propane blend, reaching the maximum brake torque (MBT) without knocking in the four boosted conditions is feasible. The presence of knock limited the advance of combustion phasing and decreased the gross indicated thermal efficiency (ITEg) with E10 gasoline and 25% and 30% DME in propane blends under 1.0 and 1.1 bar boosted conditions. In these knock-limited circumstances, the NOx emissions decreased due to the retarded phasing, and THC and PN emissions increased due to the lower combustion stability, considerably raising the concentration of accumulation mode particles in the particle size distribution (PSD) compared to the other fuel blends tested.&lt;/div&gt;

Soy-based biodiesel can reduce well-to-wheels greenhouse gas (GHG) emissions per unit energy (i.e., gCO 2 e/MJ) by 66%–72% as compared to the petroleum-based diesel fuel with currently adopted agricultural and industrial practices. Biodiesel can reduce particulate matter and carbon monoxide emissions with a manageable degree of increase in NOx emissions. From the perspective of GHG emissions reduction per unit travelling distance (i.e., gCO 2 e/mile), the application of B20 in compression ignition engines without the adjustment in engine control unit (ECU) settings will not extract the best carbon emissions reduction that B20 could achieve. Optimizing the engine control settings permits re-calibration to achieve the maximum brake fuel conversion efficiency (BFE) based on comprehensive understanding on the impact of both “fuel” and “ECU calibration” on BFE and other criteria pollutant emissions. The maximum GHG emissions reduction with B20 application is experimentally measured with the optimized ECU calibration, thus providing the understanding of the combined impact of biodiesel fuel and calibrations on engine performance and emissions. Six steady operating modes were considered, that can be combined to estimate the US federal test procedure BFE and emissions over the Federal Test Protocol (FTP) 75 cycle. Combined with the weight factors to simulate the EPA FTP 75 cycle from these 6 “mini-map” test points, 0.53% improvement in the energy requirement per unit traveling distance (i.e., MJ/mile) is achieved for B20 with the final ECU calibration, in addition to the degree of GHG emissions reduction on a “gCO 2 e/MJ” basis from the use of B20 blend of soy biodiesel of ∼12.5% reduction in gCO 2 e/MJ, for a total GHG emissions reduction of 13%.

The worldwide consensus is that global climate change is being driven by humanity’s release of fossil carbon into the atmosphere since the Industrial Revolution. Acting on the challenge of reducing fossil fuel and, particularly, petroleum consumption is our collective task. The need to act can seem daunting, given the enormous amount of petroleum that is consumed on a daily basis around the world, which has reached nearly 100 million barrels per day. However, humanity has seen major changes in our reliance on energy resources, in transportation and other sectors, over the last two centuries. Those changes have gotten us into this situation, but they provide more hope for our next transition as well. We can and must expand the adoption of low-carbon intensity renewable fuels, and we must do so in less than three decades, if we hope to limit the global temperature increase to less than 2°C. This paper provides a brief historical perspective on the use of transportation fuels and the transition that humanity must achieve and reports on a recent demonstration to support that transition.

Volvo’s SuperTruck 2 (ST2) built on the success of the SuperTruck 1 (ST1) project, with the objective to research, develop, and demonstrate a Class 8 long-haul tractor-trailer concept truck designed with an integrated approach to maximize freight efficiency and achieve the following goals: - Greater than 100% improvement in vehicle freight efficiency (FE) on a ton-mile-per-gallon basis, with a stretch goal of 120% improvement relative to a 2009 baseline. - Greater than or equal to 55% engine brake thermal efficiency (BTE) demonstrated in an operational engine at a 65-mph cruise point on a dynamometer. - Develop technologies that are commercially cost effective in terms of a simple payback. This cooperative agreement with the US Department of Energy (DOE) had a total project cost of $40,000,000 with a 50% cost share, or $20,000,000, paid by the DOE. This project was awarded to Volvo Technology of America, LLC, who was the prime recipient and project lead. Metalsa, Michelin, Wabash, Bergstrom, University of Michigan, Oak Ridge National Laboratory, Johnson Matthey, Knight Transportation, Wegmans, and Motivo were partners / sub-recipients in this project.

The prohect goal is to develop and demonstrate a microalgae bio-blendstock with greater than 60% greenhouse gas reduction potential relative to petroleum diesel, that can reduce sooting propensity, increase cetane number and improve engine thermal efficiency relative to a baseline diesel engine operating on conventional fuel.

Aquatic microalgae are a highly promising feedstock for the production of biocrude and tailored biofuels, with distinct advantages over traditional terrestrial crops, such as reduced land use and avoidance of food production competition. However, unlocking their full potential requires the development of biofuels with low life cycle greenhouse emissions biofuels, such as algae biofuels, which can significantly reduce the environmental impact of the transportation systems without requiring a complete overhaul of existing engine technology. In this study, we employ cutting-edge data-based AI modeling techniques to optimize the performance of heavy-duty engines, with a focus on transitioning towards biofuels with low life cycle greenhouse emissions biofuels. Our methodology offers significant advantages over traditional sweep testing, enabling efficient and accurate optimization of engine performance with minimal time and resources consumption. Our findings demonstrate the potential of utilizing this approach, with up to 55% NOx emissions reductions and up to 2% reduction in fuel consumption compared to the baseline optimized point. Moving forward, we plan to utilize a 30% blend of algae biofuels with diesel fuel, with the ultimate goal of achieving up to 60% lifecycle GHG emissions. Lastly, we plan to compare the results with 100% renewable biodiesel to add an additional dimension of investigating the impact of fuel chemistry on engine optimization. Overall, this study underscores the vital importance of biofuels for reducing the carbon footprint of the transportation sector and supporting a sustainable future. By harnessing the power of data-based AI modeling with low life cycle greenhouse emissions biofuels, we can accelerate the adoption of more environmentally friendly transportation systems and reduce their impact on the planet. Our findings contribute to this transition and offer insights for developing efficient and effective strategies for addressing global climate change.

The overall objective of the project is to develop and demonstrate a microalgae bio-blendstock with greater than 60% greenhouse gas reduction potential relative to petroleum diesel, that can reduce sooting propensity, increase cetane number and improve engine thermal efficiency relative to a baseline diesel engine operating on conventional fuel. Overall, the project achieved the proposed objectives including producing the final tangible deliverable. A sample of algal bioblendstock was analyzed by National Renewable Energy Laboratory (NREL) staff and partners at Yale University. In addition, the work outlined in this report provides substantial new knowledge on the subjects of algae cultivation, algae conversion to biocrude, biocrude upgrading and combustion optimization.

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Exhaust Gas Recirculation (EGR) coolers are widely used on diesel engines to reduce in-cylinder NOx formation. A common problem is the accumulation of a fouling layer inside the heat exchanger, mainly due to thermophoresis that leads to deposition of particulate matter (PM), and condensation of hydrocarbons (HC) from the diesel exhaust. From a recent investigation of deposits from field samples of EGR coolers, it was confirmed that the densities of their deposits were much higher than reported in previous studies. In this study, the experiments were conducted in order to verify hypotheses about deposit growth, especially densification. An experimental set up which included a custom-made shell and tube type heat exchanger with six surrogate tubes was designed to control flow rate independently, and was installed on a 1.9 L L-4 common rail turbo diesel engine. The test cycle and conditions were higher PM/ lower HC with 75°C coolant temperature for 1.5h, then lower PM/ higher HC with 75°C or 35°C coolant temperature for 0.5h, which was repeated 3 times. Deposits from a tube were collected every cycle for a total of 6h. In the analysis, the deposit surface was observed with a scanning electron microscope, thickness was measured by an optical microscope, and the volatile content was analyzed by a thermogravimetric analyzer (TGA). The results of this study showed that including the cold coolant condition cycle could keep higher heat exchanger effectiveness compared to the hot coolant condition, even though total deposit weight was almost the same. In addition, growth of the deposit thickness was not seen with the cold coolant condition, which was confirmed via the measurements of deposit densification. These data indicate that there is possibly a correlation between repeated hydration of the deposit by condensed water and drying.&lt;/div&gt;&lt;/div&gt;