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1

Effect of hydrogen-diesel quantity variation on brake thermal efficiency of a dual fuelled diesel engine

Debnath B. K., Saha U. K., Sahoo N.

Journal of Power Technologies

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2012

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Vol. 92, nr 1

55-67

EN

The twenty first century could well see the rise of hydrogen as a gaseous fuel, due to it being both environment friendly and having a huge energy potential. In this paper, experiments are performed in a compression ignition diesel engine with dual fuel mode. Diesel and hydrogen are used as pilot liquid and primary gaseous fuel, respectively. The objective of this study is to find out the specific composition of diesel and hydrogen for maximum brake thermal efficiency at five different loading conditions (20%, 40%, 60%, 80% and 100% of full load) individually on the basis of maximum diesel substitution rate. At the same time, the effects on brake specific fuel consumption, brake specific energy consumption, volumetric efficiency and exhaust gas temperature are also observed at various liquid gaseous fuel compositions for all the five loadings. Furthermore, second law analysis is carried out to optimize the dual fuel engine run. It is seen that a diesel engine can be run efficiently in hydrogen-diesel dual fuel mode if the diesel to hydrogen ratio is kept at 40:60.

2

A simple chemical engine in steady and dynamic situations

Sieniutycz S.

Archives of Thermodynamics

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2007

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Vol. 28, no. 2

57-84

EN

We transfer to the realm of chemical engines a method of thermodynamic optimization that was developed earlier for thermal machines aimed at maximum production of power. Steady-state model refers to the situation when two reservoirs are infinite, whereas an unsteady model treats a dynamical case with finite upper reservoir and gradually decreasing chemical potential of the active component of fuel. In the considered chemical systems total power output is maximized at constraints which take into account dynamics of mass transport and efficiency of power generation. Methods of dynamic optimization, especially dynamic programming, lead to kinetic limits estimated in form of an optimal function that describes integral power output and extends the reversible chemical work W[rev] to finite rate situations. Optimization results lead to energy limits in chemical systems subject to dissipative effects caused by rates of chemical reaction and transport phenomena. Finite-rate results include irreducible losses caused by mass transfer resistances to the classical work potential. Functions of extremum power, which incorporate a residual minimum of entropy production, are formulated in terms of initial and final states, total duration and (in a discrete process) number of stages.

3

Limiting power in imperfect systems with fluid flow

Sieniutycz S.

Archives of Thermodynamics

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2004

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Vol. 25, no. 2

69-80

EN

We develop a simple formula for the efficiency of imperfect energy converters and then apply it to the irreversible extension of the classical problem of maximum mechanical work. The work is the cumulative effect obtained from a system composed of: a resource fluid at flow, a set of sequentially arranged engines, and an infinite bath. In the engine mode the fluid's temperature T decreases along the path, thus tending to the bath temperature [T^e]. In the heat-pump mode the process direction is inverted and the fluid is heated (thermal utilization). In a related classical problem the process rates vanish due to the reversibility; here, however, finite rates und unavoidable losses of the work potential are admitted. The method of variational calculus leads to a finite-rate generalization of the maximum-work potential called the finite-rate exergy. This finite-rate exergy is a function of the usual thermal coordinates and the overall number of transfer units tau. The resulting bounds onthe work delivered or supplied are stronger than the reversible bounds predicted by the classical thermodynamics.

4

Thermodynamic limits for work-assisted and solar assisted mass transfer operations

Sieniutycz S.

Archives of Thermodynamics

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2001

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Vol. 22, nr 3-4

17-36

EN

We displey a basic thermodynamic approach to endoreversible limits' of work that may be produced or consumed by a single resource flowing in an open system. To evaluate these limits we consider sequential work-assisted unit operations, in particular those of heating, evaporation and drying which run jointly with 'endoreversible' thermal machines (e.g. heat pumps.) We also compare structures of optimization criteria describing these limits in conventional operations of mass transfer and in work-assisted operations. Mathematical analogies between entropy production expressions in these two sorts of operations are helpful to formulate optimization criteria in both cases. In work-assisted unit operations, total power input is minimized at constraints which take into account dynamics of heat and mass transport and rate of work consumption. Finite-rate, endoreversible models include irreducible losses caused by thermal resistances to the classical exergy potential. Functions of extremum work, which incorporate residual minimum entropy production, are formulated in terms of initial and final states, total duration and (in discrete processes) number of stages. With a radiative engine as an example, extension of the present approach to thermodynamic limits of nonlinear processes is also discussed.

5

Thermodynamic Criteria for Optimization of Work-Assisted and Conventional Drying Operations

Sieniutycz S., Szwast Z.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2000

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Vol. 48, nr 3

315-332

EN

This work presents thermodynamic criteria for optimization of work-assisted drying operations and compares these criteria with those conventional drying operations in sequential systems. For the work-assisted operations, which run jointly with thermal machines, such as heat pumps, total power input is minimized at constrains which describe dynamics of energy and mass exchange. Finite-rate models take into account irreducible consumption of the classical exergy caused by lossy elements in the system. Optimal work functions, which incorporate a residual entropy production, are found in terms of end states, duration and (in discrete processes) number of stages. Mathematical analogies between entropy production expressions in work-assisted and conventional operations are helpful to formulate optimization criteria of the former.