Second Law Assessment of a Wet Ethanol Fuelled HCCI Engine Combined With Organic Rankine Cycle

Abstract

In this study, first and second law analyses of a new combined power cycle based on wet ethanol fuelled homogeneous charge compression ignition (HCCI) engine and an organic Rankine cycle are presented. A computational analysis is performed to evaluate first and second law efficiencies, with the latter providing good guidance for performance improvement. The effect of changing turbocharger pressure ratio, organic Rankine cycle (ORC) evaporator pinch point temperature, turbocharger compressor efficiency, and ambient temperature have been observed on cycle's first law efficiency, second law efficiency, and exergy destruction in each of its component. A first law efficiency of 41.5% and second law efficiency of 36.9% were obtained for the operating conditions (To = 300 K, r" = 3, f]j = 80%). The first law efficiency and second law efficiency of the combined power cycle significantly vaiy with the change in the turbocharger pressure ratio, but the change in pinch point temperature, turbocharger efficiency, and ambient temperature shows small variations in these efficiencies. Second law analysis demonstrates well how the fuel exergy is used, lost, and reused in all of the cycle components. It was found that 78.9% of the total input exergy is lost: 2.0% to the environment in the flue and 76.9% due to irreversibilities in the components. The biggest exergy loss occurs in the HCCI engine which is 68.7%, and the second largest exergy loss occurs in catalytic converter, i.e., nearly 3.13%. Results clearly show that performance evaluation based on first law analysis alone is not adequate, and hence more meaningful evaluation must include second law analysis.

Thermodynamic analysis and utilisation of wet ethanol in homogeneous charge compression ignition engine

“…ethanol (bio-ethanol) in HCCI engine and its analysis via exergy method. Equations used for evaluating performance parameters have been referred from Trivedi, Khaliq, and Sharma (2010), Khaliq, Trivedi, and Dincer (2011), and Khaliq and Trivedi (2012). These equations are applied according to sub-system's operational and boundary conditions.…”

“…It is observed that combined cycle has improved thermal and exergy efficiencies by recovering some of the thermal energy of the exhaust gases to develop more efficient and environment friendly engine thus utilising waste exergy and reducing thermal pollution. The papers Khaliq, Trivedi, and Dincer (2011) and Khaliq and Trivedi (2012) deal with the study of HCCI engine performance based on ambient temperature variation (T 0 ), pressure ratio (Pr), turbocharger compressor efficiency (η c ) and pinch point on the system performance. However in the present paper, the work has been extended further to evaluate the performance of HCCI engine on the basis of variation of effectiveness of regenerator.…”

“…Effect of ambient temperature was also observed on all these parameters. Khaliq and Trivedi (2012) further conducted the second law assessment of combined cycle of HCCI engine which is also operated by wet ethanol and it is coupled with organic Rankine cycle using R113 as working fluid. It is observed that combined cycle has improved thermal and exergy efficiencies by recovering some of the thermal energy of the exhaust gases to develop more efficient and environment friendly engine thus utilising waste exergy and reducing thermal pollution.…”

“…For the transient operation of an open system such as HCCI engine and its sub-components which are experiencing mass exchange with the surroundings, the following equation is applied for the evaluation of total energy, entropy and exergy (Bejan 2006;Khaliq and Trivedi 2012):…”

Understanding Loss Mechanisms and Identifying Areas of Improvement for HCCI Engines Using Detailed Exergy Analysis

“…Exergy analysis has been applied to spark ignited and diesel engines in several prior studies [1][2][3] to explore the interaction of loss mechanisms with different engine design and operating parameters. In an HCCI context, exergy analysis has been applied in prior studies [3][4][5] as well, however many of these prior studies significantly simplify the in-cylinder processes and approximate Contributed by the Cotnbustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received April 14,2013; final manuscript received May 16, 2013; pubhshed online July 31, 2013.…”