Seamus Patrick Kane

Anhydrous ammonia (NH ₃ ) is a zero-carbon fuel that has a higher volumetric energy density and can be more easily transported and stored than gaseous or liquid hydrogen. Challenges associated with ammonia’s low laminar flame speed and high ignition energy have limited its use in the past. Many experimental efforts have attempted to overcome these limitations in internal combustion engines by blending ammonia with hydrogen or another higher reactivity fuel; however, reducing complexity by enabling pure ammonia fueling is desirable from the perspective of widespread implementation. This experimental study investigates the full operating map of a single-cylinder version of a 6.7-L displacement diesel engine retrofitted for 100% ammonia spark ignition (SI) operation. Performance and emissions measurements were completed across the full operational map with additional sweeps of spark timing and equivalence ratio conducted at selected conditions. The engine maintained stable operation above 4 bar IMEP _g across the entire tested map and maintained gross fuel consumption values of 250 g/kWh diesel equivalent or less when above idle speed and 50% load. Slightly rich (φ = 1.025 ± 0.015) operation was maintained across the test conditions to minimize the three emissions of interest (NH ₃ , NO _x , and N ₂ O) and was controlled using the measured raw NO _x concentration. Emissions control using exhaust NO _x concentration, as opposed to O ₂ , proved to be a promising approach to maintain constant NH ₃ /NO _x ratios across a large portion of the operational map.

Ammonia combustion is a topic of active research due to the need for fuel decarbonization. Although ammonia does not contain carbon, its use in internal combustion engines (ICEs) may still form nitrogen-containing ultrafine particulate matter. This work investigates particulate emissions from NH3–H2–air combustion in a single-cylinder Waukesha cooperative fuel research (CFR) octane engine under a range of hydrogen blending and engine load. Particle size distributions were quantified using a Scanning Mobility Particle Sizer (SMPS). A dual-stage dilution sampling system was used to reduce unburned ammonia concentration and maintain particle concentration within the instrument limits. The engine was motored to measure crankcase particle emissions from lubricant oil atomization. Additionally, 100% hydrogen-fueled experiments were conducted to evaluate the effect of combustion on particulate emissions from lubricant oil atomization without NH3-based particulate formation. Various ammonia–hydrogen fuel blends were tested to quantify the contribution of ammonia-based particulate matter in the exhaust. The elevated particle number concentration as the ammonia fraction rises suggests that combustion with ammonia leads to higher particulate emissions compared to hydrogen combustion at the equivalent peak in-cylinder pressure. Additionally, the presence of both unburned ammonia and NO2 in the exhaust indicate that the measured particles may consist of ammonium nitrate based on known chemical mechanisms. Modeling suggests that NH3 and NO2 found in cold regions of the combustion chamber have the potential to form gas-phase ammonium nitrate that later condenses to form particles in the exhaust system.

Metallic monolith structures are often used in compact reactor applications due to their superior heat transfer properties and lower pressure drop when compared to ceramic monoliths. Endothermic reactions like steam reforming depend heavily on externally supplied heat, making highly conductive supports especially useful. Simulations are invaluable for designing effective reactors with complex catalyst support structures but are conventionally resource-intensive. Additionally, few dedicated heat transfer experiments between monoliths exist in prior literature. To expand general knowledge of heat transfer between metal monolith structures, this work investigated heat exchange in concentric monoliths brazed to a common mantle. A computationally inexpensive quasi-dimensional model was developed and used to predict the heat exchange effectiveness and intrinsic heat transfer rate. The model used a discretized control volume approach and simplified geometries to reduce computational intensity. The model was calibrated against experimental data collected using a steady-state flow bench. After calibration, a parametric study was performed where monolith construction and flow conditions were varied. A parametric analysis showed that for identical catalyst space velocities and volumes, heat exchange effectiveness can be increased by 43.2% and heat transfer rates by 44.8% simply through increasing the surface area to volume ratio of the monolith. The described approach serves as an alternative framework for modeling catalytic heat exchangers without heavy computation and for quickly matching monolith geometries to their intended use and operating range.

Carbon-free emissions and stable operation of ammonia-fueled internal combustion engines have been demonstrated in recent studies through combustion strategies suited to the fuel’s unique properties. High ignition energy and slow flame speed of ammonia are typically compensated for by hydrogen addition and/or enhanced ignition systems while the high octane rating of ammonia allows high compression ratio. The experimental study in this work investigates the performance of ammonia in spark-assisted compression-ignition (SACI) mode, where the cylinder charge is spark ignited and a subsequent auto-ignition event results in a faster burn and more ideal combustion phasing. The high-compression ratio engine was fueled by 100% anhydrous ammonia or blends with small quantities of hydrogen (2.5% and 5% by volume). Fuels were port-injected for a homogeneous intake charge mixture at stoichiometric equivalence ratio. Two different engine speeds were tested at several intake temperatures and spark timings. All cases showed an inflection point in the apparent heat release rate (AHRR) followed by more rapid rate of heat release, signaling the onset of auto-ignition. Blending hydrogen in the fuel benefited gross indicated mean effective pressure (gIMEP) at maximum brake torque (MBT) timing, but pure ammonia fuel was more stable across a wide range of spark timings and intake temperatures. Burn durations in the present study were similar to those of conventional SI engines fueled by gasoline indicating that the combustion enhancement of SACI compensated for the lower flame speed of ammonia. The control of SI percent, defined as the fraction of heat release before auto-ignition compared to the total heat release, is shown to be strongly related to the sensitivity of auto-ignition timing to spark timing. Unburned ammonia emissions are hypothesized to be primarily driven by unburned gases trapped in the crevices and are mitigated slightly through blending hydrogen in the fuel or by increasing intake temperature. However, the addition of hydrogen and increasing intake temperature led to increased nitric oxide (NO) emissions. Of primary concern because of its potent global warming potential, nitrous oxide (N2O) did not show a clear trend with fuel hydrogen content or intake temperature, but definitively increased for the higher engine speed.

Anhydrous ammonia (NH₃) is a promising carbon-free fuel for internal combustion engines (ICEs) that can be generated from renewable energy sources and stored at high energy density. Ammonia is typically mixed with a small fraction of hydrogen (H₂), which serves as combustion promoter to achieve stable combustion over a large range of engine operation. To overcome the difficulties of storing hydrogen, ammonia can be converted to hydrogen onboard by means of a catalytic reactor fed by waste thermal energy from the engine exhaust or by partial oxidation. This work explores an alternative method of producing hydrogen by homogeneous partial oxidation of ammonia to hydrogen in an engine cylinder. Such an approach eliminates the need for costly catalyst materials and poses the possibility of a dedicated reforming cylinder to provide hydrogen for other cylinders in a multi-cylinder engine. Experiments were conducted in a single-cylinder spark-ignition (SI) engine with parametric sweeps of intake temperature, intake pressure, equivalence ratio, and spark timing. Experimental results show that 8% (dry) exhaust gas hydrogen concentration is attainable and 60% of the unburned fuel can take the form of hydrogen, particularly at rich equivalence ratios and elevated intake temperatures. CHEMKIN modeling yields insights into the hydrogen production kinetics throughout the engine cycle, revealing that initial consumption of ammonia is advanced of hydrogen production and that higher temperatures favor more hydrogen production, in agreement with experimental trends.

A thermochemical recuperation (TCR) reactor was developed and experimentally evaluated with the objective to improve dual-fuel diesel–ammonia compression ignition engines. The novel system simultaneously decomposed ammonia into a hydrogen-containing mixture to allow high diesel fuel replacement ratios and oxidized unburned ammonia emissions in the exhaust, overcoming two key shortcomings of ammonia combustion in engines from the previous literature. In the experimental work, a multi-cylinder compression ignition engine was operated in dual-fuel mode using intake-fumigated ammonia and hydrogen mixtures as the secondary fuel. A full-scale catalytic TCR reactor was constructed and generated the fuel used in the engine experiments. The results show that up to 55% of the total fuel energy was provided by ammonia on a lower heating value basis. Overall engine brake thermal efficiency increased for modes with a high exhaust temperature where ammonia decomposition conversion in the TCR reactor was high but decreased for all other modes due to poor combustion efficiency. Hydrocarbon and soot emissions were shown to increase with the replacement ratio for all modes due to lower combustion temperatures and in-cylinder oxidation processes in the late part of heat release. Engine-out oxides of nitrogen (NO_x) emissions decreased with increasing diesel replacement levels for all engine modes. A higher concentration of unburned ammonia was measured in the exhaust with increasing replacement ratios. This unburned ammonia predominantly oxidized to NO_x species over the oxidation catalyst used within the TCR reactor. Ammonia substitution thus increased post-TCR reactor ammonia and NO_x emissions in this work. The results show, however, that engine-out NH₃-to-NO_x ratios were suitable for passive selective catalytic reduction, thus demonstrating that both ammonia and NO_x from the engine could be readily converted to N₂ if the appropriate catalyst were used in the TCR reactor.

Dual-fuel strategies can enable replacement of diesel fuel with low reactivity biofuels like hydrous ethanol. Previous work has shown that dual-fuel strategies using port injection of hydrous ethanol can replace up to 60% of diesel fuel on an energy basis. However, they yield negligible benefits in NOX emissions, soot emissions, and brake thermal efficiency (BTE) over conventional single fuel diesel operation. Pretreatment of hydrous ethanol through steam reforming before mixing with intake air offers the potential to both increase BTE and decrease soot and NOX emissions. Steam reforming can upgrade the heating value of the secondary fuel through thermochemical recuperation (TCR) and produces inert gases to act as a diluent similar to exhaust gas recirculation. This study experimentally investigated a novel thermally integrated steam reforming TCR reactor that uses sensible and chemical energy in the exhaust to provide the necessary heat for hydrous ethanol steam reforming. An off-highway diesel engine was operated at three speed and load settings with varying hydrous ethanol flow rates reaching fumigant energy fractions of up to 70%. The engine achieved soot reductions of close to 90% and minor NOX reductions; however, carbon monoxide and unburned hydrocarbon emissions increased. A first law energy balance using the experimental data shows that the developed TCR system effectively upgraded the heating value of the secondary fuel. Overall, hydrous ethanol steam reforming using TCR can lead to 23% increase in fuel heating value at 100% conversion, a limit approached in the conducted experiments.