Availability analysis on combustion of n-heptane and isooctane blends in a reactivity controlled compression ignition engine

Abstract

Unfortunately, energy demands and destruction of the environment from uncontrolled manipulation of fossil fuels have increased. Climate change concerns have resulted in the rapid use of new, alternative combustion technologies. In this study, reactivity controlled compression ignition (RCCI) combustion, which can simply be exploited in internal combustion (IC) engines, is investigated. To introduce and identify extra insightful information, an exergy-based study was conducted to classify various irreversibility and loss sources. Multidimensional models were combined with the primary kinetics mechanism to investigate RCCI combustion, incorporating the second law of thermodynamics. The n-heptane, a highly reactive fuel, was supplied by direct injection into the cylinder, whereas premixed fuel was supplied through the intake port in an isooctane/n-heptane RCCI engine. For five n-heptane increments (5%, 7.5%, 15%, 25%, and 40%) and six different exhaust gas recirculation (EGR) rates (0%, 10%, 20%, 30%, 40%, and 50%), accumulation of different exergy terms was calculated. The results show that as EGR introduction increases from 0% to 50%, the exergy destruction increases from 21.1% to 28.9%. Furthermore, the value of exhaust thermomechanical exergy decreases from 18.4% to 14.4% of the mixture fuel chemical exergy. Among the five different high reactive fuel mass regimes, the 40% n-heptane mass fraction has the major heat transfer exergy owing to its advanced CA50 that exerts a unique influence on cylinder charge temperature of heat transfer layer. The utilization efficiency of exhaust in RCCI is less affected by the variation of reactive fuel mass fraction by contrast; it will significantly influence heat transfer availability. This study revealed that with increasing reactive fuel (n-heptane) from 7.5% to 40% the irreversibility decreased from 28.6% to 25.8% and the second law efficiency first increased from 43.2% to 44.6% at 15% n-heptane then decreased to 42.9% at 40% n-heptane.

Microgravity Spherical Droplet Evaporation and Entropy Effects

“…In a multicomponent gas mixture with N number of species, we considered an arbitrary differential fluid element with a volume of ∆x•∆y•∆z and constant dimension sizes, as illustrated in Figure 1. For this control volume (CV), several factors contribute to the balance of the entropy: tropy generation in conjunction with diminished heat transfer losses could more definitively define the LTC regime [27][28][29][30]. In this regard, Mahabadipour et al [31,32] used a dual fuel diesel-natural gas LTC engine model to study entropy and exergy to quantify thermodynamic irreversibilities, as well as entropy generation.…”

“…Incorporating Equation (31) into Equation (28) and comparing it to Equation (29) gives the below set of relations for each contribution to the entropy generation rate. The entropy generated due to heat transfer while incorporating conduction and radiation heat transfers can be expressed as follows:…”

“…It has recently been indicated in the literature that the second law of thermodynamics can act as a useful tool to identify LTC regions and can provide a potential means of improving overall efficiencies by analyzing the availabilities and irreversibilities of the system. Indeed, lower entropy generation in conjunction with diminished heat transfer losses could more definitively define the LTC regime [ 27 , 28 , 29 , 30 ]. In this regard, Mahabadipour et al [ 31 , 32 ] used a dual fuel diesel–natural gas LTC engine model to study entropy and exergy to quantify thermodynamic irreversibilities, as well as entropy generation.…”