Vehicle Thermal Management Systems Conference Proceedings (VTMS11)

15-16 May 2013, Coventry Technocentre, UK

Institution of Mechanical Engineers

• Publisher: Woodhead Publishing
• Year: 2013
• Print ISBN: 9780857094728
• eBook ISBN: 9780857094735
• Topic: Technology & Engineering
• Subtopic: Construction & Architectural Engineering
• Index: Technology & Engineering

The challenges facing vehicle thermal management continue to increase and optimise thermal energy management must continue as an integral part of any vehicle development programme. VTMS11 covers the latest research and technological advances in industry and academia, automotive and off-highway. Topics addressed include: IC engine thermal loading, exhaust and emissions; HEV, EV and alternative powertrain challenges; Waste heat recovery and thermodynamic efficiency improvement; Cooling systems; Heating, A/C, comfort and climate control; Underhood heat transfer and air flow management; Heat exchange components design, materials and manufacture; Thermal systems analysis, control and integration. - Covers the latest research and technological advances - Brings together developments from industry and academia - Presents leading edge research on optimised thermal energy management

Engines

Study of the vehicle thermal management focused on the engine lubricant oil

A. Morita¹, A. Hosoi¹, T. Harada¹, M. Uchida², Y. Kodama² and H. Maegawa², ¹Toyota Motor Corporation, Japan; ²NIPPON SOKEN, INC., Japan

Abstract

Thermal management demand for the engine lubricant oil is becoming higher due to the compatibility of higher specific engine output and efficiency. We have analyzed and grasped heat balance of the lubricant oil in the case of recent small car, and studied the way to improve both cooling performance and warm up behavior of the oil without additional heat exchanger. In the studied case, we have confirmed and predicted the cooling performance improvement up to 10 °C at 5200 rpm-WDT high speed driving condition. In addition, the predicted warm up behavior improvement is expected to be around 2 °C hotter after running the cold start urban driving cycle.

Notations

Symbols
Q Heat transfer rate [W]	Average Nusselt number [-]
λ Heat conductivity [W/mK]	Pr Prandtl number [-]
h Heat transfer coefficient [W/ m^2 K]	r Distance from stagnation point [m]
T Temperature [K]	z Nozzle-to-piston spacing [m]
l Length [m]	d Diameter [m]
A Heat transfer area [m^2]	v Mean velocity [m/s]
m Mass [kg]	μ Oil viscosity [Pa s]
c Specific heat [J/kgK]	C Constant [-]
Re Reynolds number [-]	V Wind velocity [km/h]

Subscripts
cond Conduction	pskirt Piston skirt
conv Convection	oj Oil jet
com Combustion	o Oil
fl Fluid	of Oil film
w Wall including piston	liner Cylinder liner
p Piston	og Oil gallery
pring Piston ring	bskirt Block skirt

1 Introduction

Development of improving warm up behavior of the engine under cold start has been focused and published by many researchers which successfully indicate milestones to reduce fuel consumption (e.g. [1-3]). About a half of additional losses caused by cold start is reported to be mechanical losses, which is dominated by viscosity of the lubricant oil, clearance and tension of the sliding portions. Therefore, countermeasures for this subject would be adopting lower viscosity oil or accelerating warm up speed of the oil and the sliding portions by making full use of waste heat generated inside the engine. On the one hand, it is important to pay the greatest attention to control them under allowable temperature at severe driving conditions, where heat load to the oil tends to increase by installation of the oil jets for piston cooling. This study is focused on mechanism of the oil temperature determination and analysis of the oil heat balance. In addition, trial to improve heat transfer efficiency between the oil and the coolant, capturing the engine as a heat exchanger, was attempted and the results are described.

2 Theoretical study

2.1 Method

To understand heat balance of the engine lubricant oil in the vehicle, a 1-D thermal model was constructed by formulating hypothesis of heat transfer mechanism starting at the combustion chamber to the coolant and the air flow outside the engine. A 1-D thermal model was chosen because it is convenient and useful at starting point of design when no geometries are given. Looking at examination cases in the past which focused on the oil cooling performance, method using a 3-D thermal model for the oil temperature prediction was published [4]. This study shows good agreement with test data and proved the validity of the temperature prediction method, although heat balance analysis of the oil was not utilized. However, hence the model is elaborate, a 3D model construction may be uphill task, and may be inconvenient when considering transitional temperature analysis. Method using a 1-D model was also published by the other authors [5], however, more verification with test data seems to be desired to gain confidence.

2.2 Thermal model

Figure 1 (a) shows macroscopic heat flow of the engine mounted in the vehicle. Heat balance could be expressed as Equation (1). Most part of friction and cooling losses generated inside the engine are transported by the coolant and released by the radiator, and the heated air flow radiates rest of losses from the engine surface.

Figure 1 Thermal model: (a) macroscopic view (b) image of the engine model (c) overview of the 1-D thermal network

(1)

In this part, detail of the 1-D thermal model shown in Figure 1 (b) (c) is described. The engine used for this study is shown in Table 1, which is adopted in the mass produced vehicle with curb weight around 1000-1200 kg. Concept of the thermal model was to construct as simple as possible aiming at general use by understanding sensitive characteristics for the oil temperature, which were known from the past experience and studies made by many researchers.

Table 1

Engine specifications

Engine type	Spark ignition
Displacement	72.5 mm
Bore diameter	72.5 mm
Stroke	80.5 mm
Compression ratio	11.5

Friction losses of each moving portions were predicted by the empirical correlation with temperature dependency, based on the measurements made by motoring test that was held previous to this study. The gas temperature, and heat transfer coefficient inside the combustion chamber was predicted by the combustion model introduced in the published paper: [6]. Equation based on the correlation by Woschni was used to predict the heat transfer coefficient in this model. These values were predicted at every crank angle and delivered to the 1-D thermal model (GT-SUITE [7]) as the input heat from the gas. Heat conduction between the each section of the engine wall was determined by Equation (2), which depends on the wall geometries and material properties. Heat convection between the wall and the fluid was determined by Equation (3).

(2)

(3)

Boundary conditions of the major portions, which are sensitive to the oil temperature, are described. Heat transfer coefficient between the coolant and the jacket walls, this time, were picked up by the 3-D CFD calculation, which was done previous to this study. Essentially, the heat transfer coefficient should be given by empirical correlations for convenience especially under the situation without fixed 3-D geometries. The oil flow rate was determined by calculating pressure balance of each section. Equation (4) shows heat balance of the piston. Heat transfer...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Engines
• Heat Exchangers
• Waste Heat/Energy Recovery
• Simulation
• Underhood and Vehicle Simulation
• Alternative Powertrain/Heat and AC
• For Publication Only
• Author Index