Plamen Punov

Numerical study of the waste heat recovery potential of the exhaust gases from a tractor engine

The paper presents an analysis of the possibilities of exhaust gas heat recovery for a tractor engine with an output power of 110 kW. On the basis of a literature review, the Rankine cycle seems to be the most effective way to recover the exhaust gas energy. This approach reduces the fuel consumption and allows engines to meet future restrictions on carbon dioxide emissions. A simulation model of the engine by means of a one-dimensional approach and a zero-dimensional approach was built into the simulation code AVL BOOST, and a model of the Rankine cycle was implemented. The experimental values of the effective power of the engine, the mass flow and the exhaust gas temperature were used to validate the engine model. The energy balance of the engine shows that more than 28.9% of the fuel energy is rejected by exhaust gases. Using the engine model, the energy and the exergy of the exhaust gases were studied. An experimental study of the real working cycle of a tractor engine revealed that the engine operates most of the time at a constant speed (n = 1650 r/min) and a constant load (brake mean effective pressure, 10 bar). Finally, Rankine cycle simulations with four working fluids were carried out at the most typical operating point of the engine. The simulation results reveal that the output power of the engine and the efficiency of the engine increase within the range 3.9–7.5%. The highest value was achieved with water as the working fluid while the lowest value was obtained with the organic fluid R134a. The power obtained with water as the working fluid was 6.69 kW, which corresponds to a Rankine cycle efficiency of 15.8%. The results show good prospects for further development of the Rankine cycle.

Progress in high performance, low emissions, and exergy recovery in internal combustion engines

Summary This article first gives a brief review of thermal engines designed for terrestrial transportation since the 1900s. We then outline the main developments in the state of the art and knowledge about internal combustion engines, focusing on the increasingly stringent pollution constraints imposed since the 1990s. The general concept of high-energy performance machines is analyzed from the energy, exergy, and public health point of view and illustrated with typical examples of clean energy production and zero emissions. Whereas the energy analysis revealed high potential of waste heat recovery from both exhaust and cooling system, the exergetic analysis revealed much higher recovery potential from exhaust gases. The exergy content of exhaust gases was observed to be within the range from 10.4% to 20.2% of the fuel energy. The cooling exergy is within the range from 1.2% to 3.4% of the fuel energy. The article concludes with some perspectives for the emergence of an economic model that could be applied to land-based transport systems in the framework of energy transition by 2030. Copyright

Optimization of automotive Rankine cycle waste heat recovery under various engine operating condition

An optimization study of the Rankine cycle as a function of diesel engine operating mode is presented. The Rankine cycle here, is studied as a waste heat recovery system which uses the engine exhaust gases as heat source. The engine exhaust gases parameters (temperature, mass flow and composition) were defined by means of numerical simulation in advanced simulation software AVL Boost. Previously, the engine simulation model was validated and the Vibe function parameters were defined as a function of engine load. The Rankine cycle output power and efficiency was numerically estimated by means of a simulation code in Python(x,y). This code includes discretized heat exchanger model and simplified model of the pump and the expander based on their isentropic efficiency. The Rankine cycle simulation revealed the optimum value of working fluid mass flow and evaporation pressure according to the heat source. Thus, the optimal Rankine cycle performance was obtained over the engine operating map.

A Study of Waste Heat Recovery Impact on a Passenger Car Fuel Consumption in New European Driving Cycle

In this article the effect of waste heat recovery (WHR) system by means of Organic Rankine cycle (ORC) on passenger car engine fuel consumption was studied. A vehicle driving model was developed in order to determine the engine operating points in New European Driving Cycle (NEDC). In order to evaluate exhaust gases enthalpy and fuel consumption at engine operating points corresponding to the driving cycle the engine was experimentally tested in steady mode. The exhaust gases temperature was measured at a location situated 1.5 m downstream the exhaust valves considering that place as the inlet of ORC heat exchanger. A simulation model of ORC was developed using R245fa as a working fluid. Numerical results revealed that maximum recovered power was 1.69 kW. The contribution of the WHR system on the vehicle fuel consumption was assessed by reduction in cumulated fuel consumption for a NEDC. Applying an ORC to engine exhaust gases reduces cumulated fuel in a NEDC test from 0.441 to 0.414 kg. In relative values this reduction accounts to 5.9 %.

Study on the combustion process in a modern diesel engine controlled by pre-injection strategy

The paper aims to study the combustion process in a modern diesel engine over the engine operating map. In order to study the rate of heat release (ROHR), an automotive diesel engine was experimentally tested using the injection parameters factory defined. The experimental test was conducted over the engine operating map as the engine speed was limited to 2400 rpm. Then, an engine simulation model was developed in AVL Boost. By means of that model the ROHR was estimated and approximated by means of double Vibe function. In all engine operating points we found two peaks at the ROHR. The first is a result of the pilot injection as the second corresponds to the main injection. There was not found an overlap between both peaks. It was found that the first peak of ROHR occurs closely before top dead center (BTDC) at partial load than full load. The ROHR peak as a result of main injection begins from 4°BTDC to 18°ATDC. It starts earlier with increasing engine speed and load. The combustion duration varies from 30 oCA to 70 °CA. In order to verify the results pressure curve was estimated by means of defined Vibe function parameters and combustion duration. As a result, we observed small deviation between measured and simulated pressure curves.