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Technical Paper

Friction Reduction by Optimization of Local Oil Temperatures

2019-09-09
2019-24-0177
The reduction of engine-out emissions and increase of the total efficiency is a fundamental approach to reduce the fuel consumption and emissions of vehicles driven by combustion engines. Conventional passenger cars are operated mainly in lower partial loads most of their lifetime. Under these conditions, oil temperatures which are far below the maximum temperatures allowed, dominate inside the journal bearings. Therefore, the objective of this research project was to investigate possible potentials of friction reduction by optimization of the thermal management of the oil circuit of a combustion engine. Within the engine investigations, it was shown that especially the friction of the main and connecting rod bearings can be reduced with an increase of the oil supply temperature.
Technical Paper

A Simulation Study of Optimal Integration of a Rankine Cycle Based Waste Heat Recovery System into the Cooling System of a Long-Haul Heavy Duty Truck

2018-09-10
2018-01-1779
As a promising solution to improve fuel efficiency of a long-haul heavy duty truck with diesel engine, organic Rankine cycle (ORC) based waste heat recovery system (WHR) by utilizing the exhaust gas from internal combustion engine has continuously drawn attention from automobile industry in recent years. The most attractive concept of ORC-based WHR system is the conversion of the thermal energy of exhaust gas recirculation (EGR) and exhaust gas from Tailpipe (EGT) to kinetic energy which is provided to the engine crankshaft. Due to a shift of the operating point of the engine by applying WHR system, the efficiency of the overall system increases and the fuel consumption reduces respectively. However, the integration of WHR system in truck is challenging by using engine cooling system as heat sink for Rankine cycle. The coolant mass flow rate influences strongly on the exhaust gas bypass which ensures a defined subcooling after condenser to avoid cavitation of pump.
Technical Paper

Experimental Investigation of Flame-Wall-Impingement and Near-Wall Combustion on the Piston Temperature of a Diesel Engine Using Instantaneous Surface Temperature Measurements

2018-09-10
2018-01-1782
The heat transfer process in a reciprocating engine is dominated by forced convection, which is drastically affected by mean flow, turbulence, flame propagation and its impingement on the combustion chamber walls. All these effects contribute to a transient heat flux, resulting in a fast-changing temporal and spatial temperature distribution at the surface of the combustion chamber walls. To quantify these changes in combustion chamber surface temperature, surface temperature measurements on the piston of a single cylinder diesel engine were taken. Therefore, thirteen fast-response thermocouples were installed in the piston surface. A wireless microwave telemetry system was used for data transmission out of the moving piston. A wide range of parameter studies were performed to determine the varying influences on the surface temperature of the piston.
Technical Paper

Wall Heat Transfer in a Multi-Link Extended Expansion SI-Engine

2017-09-04
2017-24-0016
The real cycle simulation is an important tool to predict the engine efficiency. To evaluate Extended Expansion SI-engines with a multi-link cranktrain, the challenge is to consider all concept specific effects as best as possible by using appropriate submodels. Due to the multi-link cranktrain, the choice of a suitable heat transfer model is of great importance since the cranktrain kinematics is changed. Therefore, the usage of the mean piston speed to calculate a heat-transfer-related velocity for heat transfer equations is not sufficient. The heat transfer equation according to Bargende combines for its calculation the actual piston speed with a simplified k-ε model. In this paper it is assessed, whether the Bargende model is valid for Extended Expansion engines. Therefore a single-cylinder engine is equipped with fast-response surface-thermocouples in the cylinder head. The surface heat flux is calculated by solving the unsteady heat conduction equation.
Journal Article

Some Useful Additions to Calculate the Wall Heat Losses in Real Cycle Simulations

2012-04-16
2012-01-0673
More than 20 years after the first presentation of the heat transfer equation according to Bargende [1,2], it is time to introduce some useful additions and enhancements, with respect to new and advanced combustion principles like diesel- and gasoline- homogeneous charge compression ignition (HCCI). In the existing heat transfer equation according to Bargende the calculation of the actual combustion chamber surface area is formulated in accordance with the work of Hohenberg. Hohenberg found experimentally that in the piston top land only about 20-30% of the wall heat flux values from the combustion chamber are transferred to the liner and piston wall. Hohenberg explained this phenomenon that is caused by lower gas temperature and convection level in charge within the piston top land volume. The formulation just adds the existing piston top land surface area multiplied by a specified factor to the surface of the combustion chamber.
Technical Paper

Fundamentals of Pressure Trace Analysis for Gasoline Engines with Homogeneous Charge Compression Ignition

2010-10-25
2010-01-2182
Regarding further development of gasoline engines several new technologies are investigated in order to diminish pollutant emissions and particularly fuel consumption. The Homogeneous Charge Compression Ignition (HCCI) seems to be a promising way to reach these targets. Therefore, in the past years there had been a lot of experimental efforts in this field of combustion system engineering. Negative valve overlap with pilot injection before pumping top dead center (PTDC) and an “intermediate” compression and combustion during PTDC, followed by the main injection after PTDC, is one way to realize and to proper control a HCCI operation. For conventional CI and SI combustion the pressure trace analysis (PTA) is a powerful and widely used tool to analyse, understand and optimize the combustion process.
Journal Article

Novel Transient Wall Heat Transfer Approach for the Start-up of SI Engines with Gasoline Direct Injection

2010-04-12
2010-01-1270
The introduction of CO₂-reduction technologies like Start-Stop or the Hybrid-Powertrain and the future emissions limits require a detailed optimization of the engine start-up. The combustion concept development as well as the calibration of the ECU makes an explicit thermodynamic analysis of the combustion process during the start-up necessary. Initially, the well-known thermodynamic analysis of in-cylinder pressure at stationary condition was transmitted to the highly non-stationary engine start-up. There, the current models for calculation of the transient wall heat fluxes were found to be misleading. But with a fraction of nearly 45% of the burned fuel energy, the wall heat is very important for the calculation of energy balance and for the combustion process analysis.
Technical Paper

Improvement of Engine Heat-Transfer Calculation in the Three-Dimensional Simulation Using a Phenomenological Heat-Transfer Model

2001-09-24
2001-01-3601
Improvement of heat-transfer calculation for SI-engines in the three-dimensional simulation has been achieved and widely been tested by using a phenomenological heat-transfer model. The model is based on the local application of an improved Re-Nu-correlation (dimensional analysis) proposed by Bargende [1]. This approach takes advantage of long experience in engine heat transfer modeling in the real working process analysis. The results of numerous simulations of different engine meshes show that the proposed heat-transfer model enables to calculate the overall as well as the local heat transfer in good agreement with both real working process analyses and experimental investigations. The influence of the mesh structure has also been remarkably reduced and compared to the standard wall function approach, no additional CPU-time is required.
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