Vijai Bhavani Shankar

Quantification of the Keto-Hydroperoxide (HOOCH2OCHO) and Other Elusive Intermediates during Low-Temperature Oxidation of Dimethyl Ether

This work provides new temperature-dependent mole fractions of elusive intermediates relevant to the low-temperature oxidation of dimethyl ether (DME). It extends the previous study of Moshammer et al. [ J. Phys. Chem. A 2015 , 119 , 7361 - 7374 ] in which a combination of a jet-stirred reactor and molecular beam mass spectrometry with single-photon ionization via tunable synchrotron-generated vacuum-ultraviolet radiation was used to identify (but not quantify) several highly oxygenated species. Here, temperature-dependent concentration profiles of 17 components were determined in the range of 450-1000 K and compared to up-to-date kinetic modeling results. Special emphasis is paid toward the validation and application of a theoretical method for predicting photoionization cross sections that are hard to obtain experimentally but essential to turn mass spectral data into mole fraction profiles. The presented approach enabled the quantification of the hydroperoxymethyl formate (HOOCH2OCH2O), which is a key intermediate in the low-temperature oxidation of DME. The quantification of this keto-hydroperoxide together with the temperature-dependent concentration profiles of other intermediates including H2O2, HCOOH, CH3OCHO, and CH3OOH reveals new opportunities for the development of a next-generation DME combustion chemistry mechanism.

Primary Reference Fuels (PRFs) as Surrogates for Low Sensitivity Gasoline Fuels

The authors wish to thank Adrian Ichim for performing the engine experiments. This work was supported by KAUST and the Saudi Aramco FUELCOM program.

Double Compression Expansion Engine: A Parametric Study on a High-Efficiency Engine Concept

The Double compression expansion engine (DCEE) concept has exhibited a potential for achieving high brake thermal efficiencies (BTE). The effect of different engine components on system efficiency was evaluated in this work using GT Power simulations. A parametric study on piston insulation, convection heat transfer multiplier, expander head insulation, insulation of connecting pipes, ports and tanks, and the expander intake valve lift profiles was conducted to understand the critical parameters that affected engine efficiency. The simulations were constrained to a constant peak cylinder pressure of 300 bar, and a fixed combustion phasing. The results from this study would be useful in making technology choices that will help realise the potential of this engine concept.

Optimum Heat Release Rates for a Double Compression Expansion (DCEE) Engine

The concept of double compression, and double expansion engine (DCEE) for improving the efficiency of piston reciprocating engines was introduced in SAE Paper 2015-01-1260. This engine configuration has separate high, and low pressure units thereby effectively reducing friction losses for high effective compression ratios. The presence of an additional expander stage also theoretically allows an extra degree of freedom to manipulate the combustion heat release rate so as to achieve better optimum between heat transfer, and friction losses. This paper presents a 1-D modeling study of the engine concept in GT-Power for assessing the sensitivity of engine losses to heat release rate. The simulations were constrained by limiting the maximum pressure to 300 bar. The maximum motoring pressure was varied by, (a) constraining the compression ratio of the high pressure unit, and adapting the low pressure unit accordingly, (b) changing the compression ratio of the high pressure unit with a constant geometry for the low pressure unit. The effect of maximum pressure on the brake thermal efficiency was also investigated. A final set of simulations also compared the heat release rate of the model in SAE Paper 2015-01-1260 and two other models with the same start and end of combustion. The simulations were done at engine speed of 1900 rpm, and lambda 3. The results indicate the relative insensitivity of this concept engines performance to the heat release rate when the maximum pressure constrained to a constant value of 300 bar, or even when lowering peak pressure down to 200 bar due to reduction in heat loss, and friction losses. The major limitations of the present study was the adoption of a constant convection heat loss multiplier for all the cases, and a simplistic friction model. (Less)