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Advanced combustion engines, as power sources, dominate all aspects of the transportation sector. Stringent emission and fuel efficiency standards have promoted the research interest in advanced combustion strategies and alternative fuels. Owing to the comparable energy density to the existing fossil fuels and renewable production, alcohol and ether fuels may be a suitable replacement, or an additive to the gasoline/diesel fuels to meet the future emission standards with minimal modification to current engine geometry. Furthermore, lean and diluted combustion are well-researched pathways for efficiency improvement and reduction of engine-out emissions of modern engines. However, lean-burn or EGR dilution can introduce combustion inefficiencies in the form of excessive hydrocarbon, carbonyl species and carbon monoxide emissions.

One-dimensional transient modeling techniques are adapted to analyze the thermal behavior of lean-burn after-treatment systems when active flow control schemes are applied. The active control schemes include parallel alternating flow, partial restricting flow, and periodic flow reversal (FR) that are found to be especially effective to treat engine exhausts that are difficult to cope with conventional passive flow converters. To diesel particulate filters (DPF), lean NOx traps (LNT), and oxidation converters (OC), the combined use of active flow control schemes are identified to be capable of shifting the exhaust gas temperature, flow rate, and oxygen concentration to more favorable windows for the filtration, conversion, and regeneration processes. Comparison analyses are made between active flow control and passive flow control schemes in investigating the influences of gas flow, heat transfer, chemical reaction, oxygen concentration, and converter properties.

Diesel fueling and exhaust flow strategies are investigated to control the substrate temperatures of diesel aftertreatment systems. The fueling control includes the common-rail post injection and the external supplemental fuel injection. The post injection pulses are further specified at the early, mid, or late stages of the engine expansion stroke. In comparison, the external fueling rates are moderated under various engine loads to evaluate the thermal impact. Additionally, the active-flow control schemes are implemented to improve the overall energy efficiency of the system. In parallel with the empirical work, the dynamic temperature characteristics of the exhaust system are simulated one-dimensionally with in-house and external codes. The dynamic thermal control, measurement, and modeling of this research intend to improve the performance of diesel particulate filters and diesel NOx absorbers.

With the increasing demand of emission reductions from the automotive industry, advanced after-treatment strategies have been investigated to overcome the challenges associated with meeting increasingly stringent emission regulations. Ongoing investigations on low temperature combustion (LTC) strategies are being researched to meet future emission regulations, however, the lowered exhaust temperature presents an even greater issue for exhaust after-treatment due to the change in combustion modes. Catalyst temperature is critical for the catalytic ability to maintain effective conversion efficiency of regulated emissions. The use of periodic flow reversal has shown benefits of maintaining catalyst temperature by alternating the exhaust flow direction through the catalytic converter, reducing the catalyst sensitivity to inlet gas temperature fluctuations.

In the recent decades, the emission and fuel efficiency regulations put forth by the emission regulation agencies have become increasingly stringent and this trend is expected to continue in future. The advanced spark ignition (SI) engines can operate under lean conditions to improve efficiency and reduce emissions. Under such lean conditions, the ignition and complete combustion of the charge mixture is a challenge because of the reduced charge reactivity. Enhancement of the in-cylinder charge motion and turbulence to increase the flame velocity, and consequently reduce the combustion duration is one possible way to improve lean combustion. The role of air motion in better air-fuel mixing and increasing the flame velocity, by enhancing turbulence has been researched extensively. However, during the ignition process, the charge motion can influence the initial spark discharge, resulting flame kernel formation, and flame propagation.

The ever-stringent emission regulations are major challenges for the diesel fueled engines in automotive industry. The applications of advanced after-treatment technologies as well as alternative fuels [1] are considered as promising methodology to reduce exhaust emission from compression ignition (CI) engines. Using dimethyl ether (DME) as an alternative fuel has been extensively studied by many researchers and automotive manufactures since DME has demonstrated enormous potential in terms of emission reduction, such as low CO emission, and soot and sulfur free. However, the effect of employing DME in a lean NOX trap (LNT) based after-treatment system has not been fully addressed yet. In this work, investigations of the long breathing LNT system using DME as a reductant were performed on a heated after-treatment flow bench with simulated engine exhaust condition.

Diesel Particulate Filters (DPF) are viable to reduce smoke from diesel engines. An oxidation process is usually required to remove the Particulate Matter (PM) loading from the DPF substrates. In cases when the engine exhaust temperature is insufficient to initiate a thermal regeneration, supplemental energy is commonly applied to raise the exhaust gas and/or the DPF substrate temperatures. A flow reversal (FR) mechanism that traps a high temperature region in the DPF substrate by periodically altering the gas flow directions has been identified to be capable of reducing the supplemental energy and thus to improve the overall thermal efficiency of the engine. However, extended operations with low exhaust temperature lowers the DPF boundary temperatures that defers the regeneration processes. Furthermore, the temperature fluctuations caused by the periodic FR operation also increase the thermal stress in the DPF.

Increasingly stringent emission standards have promoted the interest in alternate fuel sources. Because of the comparable energy density to the existing fossil fuels and renewable production, alcohol fuels may be a suitable replacement, or an additive to the gasoline/diesel fuels to meet the future emission standards with minimal modification to current engine geometry. In this research, the combustion characteristics of neat n-butanol are analyzed under spark ignition operation using a single cylinder SI engine. The fuel is injected into the intake manifold using a port-fuel injector. Two modes of charge dilution were used in this investigation to test the limits of stable engine operation, namely lean burn using excess fresh air and exhaust gas recirculation (EGR). The in-cylinder pressure measurement and subsequently, heat release analysis are used to investigate the combustion characteristics of the fuel under low load SI engine operation.

Advances in engine technology in recent years have led to significant reductions in the emission of pollutants and gains in efficiency. As a facet of investigations into clean, efficient combustion, the homogenous charge compression ignition (HCCI) mode of combustion can improve upon the thermal efficiency and nitrogen oxides emission of conventional spark ignition engines. With respect to conventional diesel engines, the low nitrogen oxides and particulate matter emissions reduce the requirements on the aftertreatment system to meet emission regulations. In this paper, n-butanol, an alcohol fuel with the potential to be derived from renewable sources, was used in a light-duty diesel research engine in the HCCI mode of combustion. Control of the combustion was implemented using the intake pressure and external exhaust gas recirculation. The moderate reactivity of butanol required the assistance of increased intake pressure for ignition at the lower engine load range.

Preliminary empirical and modeling analyses are conducted to evaluate the energy efficiency of in-cylinder and external fuel injection strategies and their impact on the energy required to enable diesel particulate filter (DPF) regeneration for instance. During the tests, a thermal wave that is generated from the engine propagates along the exhaust pipe to the DPF substrate. The thermal response of the exhaust system is recorded with the thermocouple arrays embedded in the exhaust system. To implement the external fuel injection, an array of thermocouples and pressure sensors in the DPF provide the necessary feedback to the control system. The external fuel injection is dynamically adjusted based on the thermal response of the DPF substrate to improve the thermal management and to reduce the supplemental energy. This research intends to quantify the effectiveness of the supplemental energy utilization on aftertreatment enabling.

Experiments are carried out with the diesel particulate filter and oxidation catalyst embedded in the active-flow configurations on a single cylinder diesel engine. The combined use of various active flow control schemes are identified to be capable of shifting the exhaust gas temperature, flow rate, and oxygen concentration to favorable windows for filtration, conversion, and regeneration processes. Empirical and theoretical investigations are performed with a transient one-dimensional single channel aftertreatment model developed in FORTRAN and MATLAB. The influence of the supplemental energy distribution along the length of aftertreatment device is evaluated. The theoretical analysis indicates that the active-flow control schemes have fundamental advantages in optimizing the converter thermal management including reduction in supplemental heating, increase in thermal recuperation, and improving overheating protection.

As European and Chinese tailpipe emission regulations for gasoline light-duty vehicles impose particulate number limits, automotive manufacturers have begun equipping some vehicles with a gasoline particulate filter (GPF). Increased understanding of how soot morphology, reactivity, and GPF loading affect GPF filtration and regeneration characteristics is necessary for advancing GPF performance. This study investigates the impacts of morphology, reactivity, and filter soot loading on GPF filtration and regeneration. Soot morphology and reactivity are varied through changes in fuel injection parameters, known to affect soot formation conditions. Changes in morphology and reactivity are confirmed through analysis using a transmission electron microscope (TEM) and a thermogravimetric analyzer (TGA) respectively.

In this work, a spatially distributed spark ignition strategy was employed to improve the ignition process of well-mixed ultra-lean dilute gasoline combustion in a high compression ratio (13.1:1) single cylinder engine at partial loads. The ignition energy was distributed in the perimeter of a 3-pole igniter. It was identified that on the basis of similar total spark energy, the 3-pole ignition mode can significantly shorten the early flame kernel development period and reduce the cyclic variation of combustion phasing, for the spark timing sweep tests at λ 1.5. The effect of ignition energy level on lean-burn operation was investigated at λ 1.6. Within a relatively low ignition energy range, i.e. below 46 mJ per pole, the increase in ignition energy via ether 1 pole or 3 pole can improve the controllability over combustion phasing and reduce the variability of lean burn combustion. Higher ignition energy was required in order to enable ultra-lean engine operation with λ above 1.6.

Extensive empirical work indicates that exhaust gas recirculation (EGR) is effective to lower the flame temperature and thus the oxides of nitrogen (NOx) production in-cylinder in diesel engines. Soot emissions are reduced in-cylinder by improved fuel/air mixing. As engine load increases, higher levels of intake boost and fuel injection pressure are required to suppress soot production. The high EGR and improved fuel/air mixing is then critical to enable low temperature combustion (LTC) processes. The paper explores the properties of the Fuels for Advanced Combustion Engines (FACE) Diesel, which are statistically designed to examine fuel effects, on a 0.75L single cylinder engine across the full range of load, spanning up to 15 bar IMEP. The lower cetane number (CN) of the diesel fuel improved the mixing process by prolonging the ignition delay and the mixing duration leading to substantial reduction of soot at low to medium loads, improving the trade-off between NOx and soot.

The push for environmental protection and sustainability has led to strict emission regulations for automotive manufacturers as evident in EURO VII and 2026 EPA requirements. The challenge lies in maintaining fuel efficiency and simultaneously reducing the carbon footprint while meeting future emission regulations. Alcohol (primarily methanol, ethanol, and butanol) and ether (dimethyl ether) fuels, owing to their comparable energy density to existing fuels, the comparative ease of handling, renewable production, and suitable emission characteristics may present an attractive drop-in replacement, fully or in part as an additive, to the gasoline/diesel fuels, without extensive modifications to the engine geometry. Additionally, lean and diluted combustion are well-researched pathways for efficiency improvement and reduction of engine-out emissions of modern engines.