Petrogenetic history of lava flows from the Casitas Shield in the Southern Volcanic Zone, Chile

Relatively few studies have investigated the geochemistry of the Descabezado Grande-Cerro Azul (DGCA) volcanic complex, located in the Southern Volcanic Zone (SVZ) of the Chilean Andes. Lava samples were collected in stratigraphic order from vertical stacks of flows exposed along the walls of steep canyons incised in the flanks of the Casitas shield of Cerro Azul. In order to determine dominant petrogenetic processes and identify changes in the composition of the magmatic system over time, this project obtained mineral analyses using x-ray fluorescence (XRF) as well as textural analyses of petrographic thin sections using scanning electron microscopy (SEM). Analyses of the younger lavas were found to be composed mostly of basalts with some basaltic andesite compositions, results that are more primitive than older lavas previously sampled in this section and throughout the Southern Volcanic Zone

An applicable approach to mitigate pressure rise rate in an HCCI engine with negative valve overlap

Low-temperature combustion in a homogeneous-charge compression-ignition (HCCI) engine offers high thermalefficiency while cutting offemissions. However, HCCI’s feasibility is hampered by excessive peak pressure riserates under high load, causing combustion noise and possible engine damage. This study considers extending thehigh-load limit in a boosted HCCI engine accommodating variable valve timing and fuel reforming during ne-gative valve overlap. Three techniques are evaluated on a research engine: (i) exhaust valve timing retardation(ii) boost pressure adjustment and (iii) reduction of fuel subjected to reforming. Two load regimes are explored:a mid-load point with indicated mean effective pressure of 0.61 MPa; and high-load conditions achieved by 25%more fuelling. The former is often reported as boundary condition for HCCI’s, the latter is usually far beyond theacceptable pressure rise rate limit. Results indicate that strategies (i) and (iii) offer a trade-off-free solution forhigh-load extension. This can be realized as a supervisory, in-cylinder pressure based, control function.Independently of the pressure rise rate mitigation method considered, two key variables are crucial for closed-loop control: the in-cylinder volume at 50% fuel burnt and the combustion duration. They are closely coupledand can be real-time calculated using well-established control framework based on sensing the combustiontiming. The expansion rate and differences in fuel mass subjected to reforming are secondary for pressure riserate estimation and should be considered if greater accuracy is required.fi=vertaisarvioitu|en=peerReviewed

Partially premixed combustion of hydrotreated vegetable oil in a diesel engine : Sensitivity to boost and exhaust gas recirculation

Hydrotreated vegetable oil (HVO) has potential to emerge as an alternative fuel to mineral diesel due to its favourable properties. The present study investigated HVO under partially premixed compression ignition combustion mode with boost-exhaust gas recirculation (EGR) and also in conventional combustion mode. Single-cylinder engine tests focused on optimising a single representative operating point in the middle of the engine operating envelope. The optimisation focused on the trade-off between NOX and particulate matter, as the adopted multi-pulse strategy provides stable combustion onset independently of the cylinder mixture conditions. Sensitivity in emissions comes from large differences in the early, premixed combustion phase. Air-path optimized HVO combustion favours higher EGR rates (25 % vs. 20 %) and lower boost pressures than diesel (130 kPa vs 165 kPa). At such conditions HVO has 1.5 percentage points higher indicated thermal efficiency (43.5 %) than diesel. At the same time, HVO yields an ultra-low particulate level (0.055 g/kWh) and engine-out NOX emissions are 46 % better than optimised diesel combustion. Together with a 37 % reduction in total hydrocarbon emissions, the elimination of aromatics also provides an additional incentive for HVO.© 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).fi=vertaisarvioitu|en=peerReviewed

Methanol-HVO blends for efficient low-temperature combustion: analytical research on fuel properties

Received: January 31st, 2023 ; Accepted: April 15th, 2023 ; Published: August 14th, 2023 ; Correspondence: [email protected] low-temperature combustion (LTC) engines can accommodate ultra-high efficiency with near-zero NOx and PM emissions. Reaction kinetics is the governing mechanism in LTC. Onboard fuel reactivity control is, thus, becoming an interesting concept that ultimately provides pathways toward a fully fuel-flexible engine. No matter the technical realisation - in-cylinder blending or pre-blending/emulsification - the reactivity control requires fuels with complementary properties. Methanol and hydrotreated vegetable oil (HVO) seem to be one of the most promising, yet under-studied combination for LTC engines. They are both renewable and can be mixed together. Methanol’s high knock resistance and large latent heat of evaporation enable a wide engine load range, with a propensity to reduce NOx emissions and mitigate thermal or mechanical stress. The same properties on the other hand require highly reactive fuel to enable the mixture to self-ignite controllably in LTC conditions. HVO is amongst the most reactive renewable alternatives and its clean paraffinic structure further mitigates particle matter formation. - Importantly, in pre-blending HVO emulsification can resolve the lubricity issues of methanol. In this paper, the aim was to study the engine-relevant properties of HVO-methanol fuel blends. The analysed properties were the distillation properties, density, kinematic viscosity, cetane index, and flash point. Based on the results, the suitability of the chosen blend shares for LTC concepts was evaluated

Excess Air Ratio Management in a Diesel Engine with Exhaust Backpressure Compensation

The paper investigates the operation of a wideband universal exhaust gas oxygen (UEGO) sensor in a diesel engine under elevated exhaust backpressure. Although UEGO sensors provide the excess air ratio feedback signal primarily in spark ignition engines, they are also used in diesel engines to facilitate low-emission combustion. The excess air signal is used as an input for the fuel mass observer, as well as to run the engine in the low-emission regime and enable smokeless acceleration. To ensure a short response time and individual cylinder control, the UEGO sensor can be installed upstream of a turbocharger; however, this means that the exhaust gas pressure affects the measured oxygen concentration. Therefore, this study determines the sensor’s sensitivity to the exhaust pressure under typical conditions for lean burn low-emission diesel engines. Identification experiments are carried out on a supercharged single-cylinder diesel engine with an exhaust system mimicking the operation of the turbocharger. The apparent excess air measured with the UEGO sensor is compared to that obtained in a detailed exhaust gas analysis. The comparison of reference and apparent signals shows that the pressure compensation correlations used in gasoline engines do not provide the correct values for diesel engine conditions. Therefore, based on the data analysis, a new empirical formula is proposed, for which the suitability for lean burn diesel engines is verified.© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).fi=vertaisarvioitu|en=peerReviewed

Algorithmics of Posets Generated by Words Over Partially Commutative Alphabets (Extended)

It is natural to try to relate partially ordered sets (posets in short) and classes of equivalent words over partially commutative alphabets. Their common graphical representation are Hasse diagrams. We investigate this relation in detail and propose an efficient online algorithm that decompresses a concurrent word to its Hasse diagram. The lexicographically minimal representative of an equivalence class of words is called the lexicographical normal form of this class. We give an algorithm which enumerates, in the lexicographical order, all distinct classes of words identified by their lexicographical normal forms. The two presented algorithms are the main contribution of this paper

An analytical approach to converting vibration signal to combustion characteristics of homogeneous charge compression ignition engines

Homogeneous charge compression ignition (HCCI) is a promising low-temperature combustion technique for low-emission internal combustion engines. Unlike conventional engines, HCCI lacks a direct ignition control mechanism, necessitating closed-loop combustion control. This study proposes a phenomenological-based, cost-effective, and non-intrusive approach using vibration data analysis to determine essential combustion parameters. Experiments were conducted on a single-cylinder research engine with an accelerometer attached to the engine head. The engine operation envelope covered the whole engine’s operating area in naturally aspirated HCCI mode. Wavelet analysis revealed that combustion-related frequencies centered around 500 Hz, independent of operating conditions. The correlation-seeking analysis included peak acceleration amplitude and its crank angle with peak heat release rate (HRR) data. The peak HRR location was accurately identified within one degree when vibration amplitude exceeded the 100 m/s2 threshold. This encompassed 98.5% of the analyzed combustion cycles. The peak HRR prediction accuracy had a maximum error below 21% and was suitable to monitor reaction rates, especially in incomplete combustion and high ringing cycles.© 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).fi=vertaisarvioitu|en=peerReviewed