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A Study on the Effect of Elevated Coolant Temperatures on HD Engines
... A lot of research has been conducted to lower the heat losses to the walls and hereby increasing the engine's efficiency. For example by lowering the in-cylinder gas temperature, by using low temperature combustion or water injection [21], or by reducing the temperature difference between the combustion gases and the combustion chamber walls, by applying ceramic coatings on the combustion chamber walls and piston [22] or operating the engine with an elevated coolant temperature [23]. Next to the efficiency, the heat transfer also affects the emission of pollutants, as many of the chemical reactions in their formation are highly dependent on the mixture's gas temperature. ...
... 23: Frequency spectrum of the pressure pulsations ...
In this work, an experimental study was performed of the heat transfer in low temperature combustion engines. The heat transfer was measured in two single-cylinder engines: a Waukesha CFR engine at Ghent University and a Scania D13 engine at Lund University. The CFR engine was operated in HCCI mode and the Scania engine in both HCCI and PPC mode. A statistical analysis was performed on the effect of the engine settings on the maximum heat flux and the total heat loss during the cycle for motored, HCCI and PPC operation of both engines. An evaluation of multiple existing heat transfer models demonstrated that these models are not suitable for predicting the instantaneous heat flux during HCCI and PPC operation. For this reason, a new heat transfer model was developed for low temperature combustion engines. A comparison with the existing heat transfer models showed that the heat transfer model is better able to predict the instantaneous heat flux, the maximum heat flux and the total heat loss.
... Low operating temperature of surfaces leads to power loss and increase fuel consumption (Shayler et al., 2005). High temperature causes problems with higher engine thermal stress and problem with knock (Singh et al., 2017). ...
... Some of these issues are addressed in the work by Singh et al. [23] on elevated coolant temperature simulations for a Scania HD engine. In this study it was seen that there exists an optimum coolant temperature for each engine operating point, for maximizing recoverable power from the coolant. ...
div class="section abstract"> Powertrain efficiency is a critical factor in lowering fuel consumption and reducing the emission of greenhouse gases for an internal combustion engine. One method to increase the powertrain efficiency is to recover some of the wasted heat from the engine using a waste heat recovery system e.g. an organic Rankine cycle. Most waste heat recovery systems in use today for combustion engines use the waste heat from the exhaust gases due to the high temperatures and hence, high energy quality. However, the coolant represents a major source of waste heat in the engine that is mostly overlooked due to its lower temperature. This paper studies the potential of using elevated coolant temperatures in internal combustion engines to improve the viability of low temperature waste heat recovery. The paper first uses engine experiments and multi-linear regression analysis to model the indicated efficiency and recoverable power for a Scania D13 heavy duty engine across a range of engine loads, speeds and coolant temperatures. The recoverable power is obtained from simulations of a dual loop waste heat recovery system using ten working fluids as potential candidates for recovering heat from the exhaust gases and the coolant. The paper then investigates the maximum potential fuel consumption benefit by using elevated coolant temperatures for the Scania engine running on the World Harmonized Transient Cycle. From the simulation results, it was seen that cyclopentane and methanol were the best performing working fluids for the coolant and exhaust gas heat sources respectively. From the analysis on the World Harmonized Transient cycle, when using the best performing working fluids and elevated coolant temperatures, a potential net reduction in fuel consumption of 9% could be obtained.
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In this paper, an investigation is done into the potential of increasing the coolant temperature of an engine to maximize the powertrain efficiency. The study takes a holistic approach by trying to optimise the combined engine and waste heat recovery system. The work was done experimentally on a Volvo 4-cylinder light duty diesel engine in combination with Rankine cycle simulations. For the study, the coolant temperature was swept from 80 °C to 160 °C at different operating points. It was seen that with increased coolant temperatures, the brake efficiency of the engine increased by up to 1 percentage point due to reduced heat losses. An optimum coolant temperature was observed, dependent on the operating point, for maximizing coolant recoverable power. An expansive study was done simulating 48 working fluids for a dual loop waste heat recovery system. From the working fluids simulated, cyclopentane was seen as the best for coolant waste heat recovery, whereas methanol and acetone were better for the exhaust gases. The gain in efficiency seen, was up to 5.2 percentage points, with up to 1.7 percentage points as the effect due to recovered power from the coolant.
This article offers a comprehensive overview of research on fuel reforming in internal combustion engines (ICE). It includes a historical perspective of research in this field, a discussion on the considerations to be made prior to choosing a primary fuel for reforming purposes, and the main processes in fuel reforming. Steam reforming offers a moderate degree of thermochemical recuperation and is applicable to methanol and ethanol feeding. Reforming with air reduces the degree of recuperation, but opens up the use of heavier fuels such as gasoline and diesel fuel. Dry reforming (with CO2) offers the best recuperation but is prone to fast coking. The choice of catalyst and the expected side reactions for each fuel are also discussed. While there is extensive literature on steam reforming catalysts and kinetics at atmospheric pressure, studies at higher pressures and/or on decomposition reactions are very few. The thermodynamics of fuel reforming in ICE and simulation approaches are also discussed. The paper also reports on engineering aspects of fuel reformer design and provides an overview of engines with thermo-chemical recuperation (TCR), fuel supply, and load control strategies in ICE with TCR. In-cylinder fuel reforming as well as application of fuel reforming for performance improvement of emission aftertreatment systems are subsequently discussed. This overview reveals ongoing diverse research activities in the field of onboard fuel reforming. However, several problems, including reformate burning velocity at typical for ICE conditions, in-cylinder behavior of directly injected reformates and particle formation still need to be addressed. A discussion on some of these unresolved issues is attempted herein.
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