Study of the Transient Operation of Low Heat Rejection Turbocharged Diesel Engine Including Wall Temperature Oscillations

Abstract

During the last decades, a vivid interest in the low heat rejection (LHR) diesel engine has arisen. In a LHR engine, an increased level of temperatures inside the cylinder is achieved resulting from the insulation applied to the combustion chamber walls. The steady-state LHR engine operation has been studied so far by applying either first-or second-law balances. However, very few works have treated this subject during the very important transient operation, with the results limited to the engine speed response. For this purpose, an experimentally validated simulation code of the thermodynamic cycle of the engine during transient conditions is applied. This takes into account the transient operation of the fuel pump, the development of friction torque using a detailed per degree crank angle sub-model, while the equations for each cylinder are solved individually and sequentially. In this work, two common insulators of various thicknesses are considered for the engine in hand, viz. silicon nitride and plasma spray zirconia. The transient response of various engine (e.g. speed, volumetric efficiency, fuel pump rack position, brake mean effective pressure and specific fuel consumption) and turbocharger variables is depicted and analyzed, with the results compared to the non-insulated transientand the insulated steady-state operation. For a more indepth analysis of transient engine heat transfer, the interesting phenomenon of the short-term temperature (cyclic) oscillations in the combustion chamber walls during transients needs to be studied. To this aim, the thermodynamic model of the engine is appropriately coupled to a wall periodic heat conduction model, which uses the gas temperature variation as boundary condition throughout the engine cycle after being treated by Fourier analysis techniques. The evolution of many variables during the transient engine cycles, such as the amplitude of oscillation or gradient of temperature swing is thus illustrated. Moreover, the simulation code is expanded in a way to include the second-law balance, as this may prove an interesting alternative to the firstlaw analysis. It is revealed that after a ramp increase in load, the second-law values unlike the first-law ones are heavily impacted by the insulation scheme applied.Combustion and total engine irreversibilities decrease significantly (up to 24% for the cases examined) with increasing insulation. Unfortunately, this decrease is not transformed into an increase in piston work but rather increases the potential for extra work recovery owing to the higher availability content of the exhaust gas.

A study of suspension plasma-sprayed insulated pistons evaluated in a heavy-duty diesel engine

“…The higher exhaust temperature for the insulated engine means an increase in the amount of energy that can be converted into work by WHR systems. 3 Insulated manifolds could also be used for reducing heat losses before the turbine or WHR systems. Serrano et al 8 have shown that insulated exhaust manifolds can increase the available energy at the inlet of the turbine and improve the efficiency of the engine compared to when only the pistons are insulated.…”

“…Higher exhaust temperatures have been observed in experiments, as well as in simulations, with TBC on combustion chamber components. 3–5 The higher exhaust energy may partly be recovered by waste heat recovery (WHR) systems. 3 Improved work on the piston seems to be more difficult to accomplish.…”

“…3–5 The higher exhaust energy may partly be recovered by waste heat recovery (WHR) systems. 3 Improved work on the piston seems to be more difficult to accomplish. Some studies with TBC in heavy-duty diesel engines show improved fuel efficiency by 6% 6 while other studies show decreased fuel efficiency by up to 8%.…”

Theoretical dynamic simulation software for slider crank mechanism of V8 engines

“…tangential force is acting at the inner wall of the cylinder, it is the dynamic load for the fatigue calculation of the cylinder block and is responsible for the oval wear of the cylinder. In order to assess the reliability of the extracted theoretical curves of Figure 6, the inertial force at the piston's tangential plane is compared with [8]. The resultant theoretical force is compared with the results of [9].…”

Running-in behaviour of thermal barrier coatings in the combustion chamber of a diesel engine

“…1–5 TBCs on combustion chamber components such as pistons, valves and cylinder heads have the potential to reduce heat losses from the combustion gases. 6,7 Lower heat losses from the combustion chamber may in turn lead to an increase in gas pressure and thus an increase in the work on the piston. 6…”