P. Bauer and J. Murillo - PowerPoint Presentation

Slide1

P.

Bauer and J. Murillo

University

of Notre DameDept. of Electrical EngineeringNotre Dame, IN 46556, USA

Biodiesel versus diesel: A comparative analysis of the effect of engine cycling on efficiency

TABLE OF CONTENTS

1 - Introduction

Preliminaries and Concepts

2 -PreliminariesBSFCCycling induced BSFCBioDiesel bsfc3 -Analytical Results

4. -Conclusions5. -Future Research

1. INTRODUCTION

Hybridization of powertrain

: fuel savings due to avoidance of high

bsfc operating regions in ICEOur focus: Large ICEs (Diesels) in a series hybrid configurationLarge ICEs in a series hybrid powertrain It is not possible to cycle between the bsfc optimal power and the engine off state

Important question: Do the advantages of cycling carry over from Diesel to Bio-Diesel ?Applications areas:

large trucks, earth moving equipment, locomotives, Diesel generators, etc.

Hardware requirements:

ICE, generator, energy buffer, inverter, e-motor(s), mechanical powertrain, engine controller.

Diesel

Engine

Generator

AC

Fuel

Rectifier

DC

Battery

Load

2. PRELIMINARIES AND

DEFINITIONS

Assume the engine will operate at discrete power levels

, in this case two power levelsDenote the two engine operating points as

,

.

Define the minimal achievable brake specific fuel consumption at an engine power level

as

Denote the power level of the global

minimum as

and the low power

OP

as

Typical full load

BSFC

ranges:

In order to illustrate the concept we will use some artificially generated bsfc curves

2. PRELIMINARIES AND DEFINITIONS

Original minimally achievable engine

BSFC

for Diesel

Cycling induced engine

for Diesel

Minimally achievable engine

BSFC

for Bio-Diesel

Cycling induced engine

BSFC for

Bio-Diesel

The difference between

BSFC

for Diesel and Bio-Diesel as function of brake power

: Engine brake power

: Brake power for which the

BSFC

minimum is reached for Diesel

: Power of low power operating point for Diesel

(2. Cont.) CYCLING: Basic Concepts

Fuel savings can be achieved by cycling in a series hybrid powertrain

The engine is operated at

two discrete operating points,

and

Average power produced is between operating point power levels and must meet power output demands

Excess

power generated at high engine power levels can be stored in an energy buffer

Stored power can be pulled from the energy buffer to compensate low engine power levels

Our analysis is asymptotic, i.e. for large cycle periods and large energy buffer

size

Cycling between

and

(2. Cont.) CYCLING: Basic Equations

Fuel mass,

M,

consumed at a power, P, over time T

Average Power,

,

as a function of time for

and

Mass

o

f fuel consumed cycling between

P

1

and

P

2

(2. Cont.) THE CYCLING INDUCED EFFECTIVE 𝒃𝒔𝒇𝒄

A new bsfc curve generated under the assumption that an engine will be cycled between two operating points

low

power operating point

at

the global bsfc minimum power level

Cycling induced fuel

consumption

often better than fuel consumption under regular operation.

(2. Cont.) A REALISTIC CASE: The Cummins B-Series EQB235-20 Diesel Engine

Fuel savings are possible in real, existing engines

Key characteristic: the “flatting out” of the engine bsfc curve

For larger engines, greater margins of fuel savings are possible

(2.

Cont

.) Bio-Diesel BSFC

Relationship between

, bsfc(P) and

.

Relationship

between

curves for regular Diesel and Bio-Diesel, with the difference between the two being denoted as

. For

practically all Bio-Diesel fuels and mixtures with regular Diesel, the efficiency drops relative to regular Diesel, i.e. the

increases:

Often

is approximately constant and not a strong function of

3. ANALYTICAL RESULTS

,

(1)

The bsfc values for Bio-Diesel is always higher than that of Diesel.

The difference between Diesel and Bio-Diesel bsfc depends on the

BioDiesel

mixture

Usually the difference between Diesel and Bio-Diesel bsfc is only a weak function of power and can often be considered constant over certain power

bands

(3.

Cont.)

ANALYTICAL RESULTS

(2)

Relationship between induced BSFC for Diesel and Bio-Diesel

The induced BSFC for Bio-Diesel is always higher than that for Diesel

The difference in the induced BSFC depends on duty cycle and the difference in BSFC values at power

and

(3. Cont.) ANALYTICAL RESULTS

(3)

Condition for cycling induced BSFC (for Bio-Diesel) to be lower (better) than the regular BSFC (for Bio-Diesel)

If the inequality is true, cycling is advantageous

(3. Cont.) ANALYTICAL RESULTS -

Key Result

(

4

)

Condition for cycling to be advantageous

If the BSFC difference between Diesel and Bio-Diesel is large in a certain power band

between

and

, and small

at

and

,

cycling is preferable.

(5)

This condition is often approximately satisfied, i.e. the BSFC difference between Diesel and BIO-Diesel is approximately constant over certain power bands

With the previous equation

(4)

this shows that in this case the advantageous of cycling carry over from Diesel to

BioDiesel

A notable case where these advantageous may not carry over is if the BSFC difference is high at P1 and

Popt

and low in between.

(3. Cont.) ANALYTICAL RESULTS

(3. Cont.) ANALYTICAL RESULTS –

Example BSFC by S.

Savariraj

et al.

(3. Cont.) ANALYTICAL RESULTS –

Example BSFC by S.

Savariraj

et al.

4.

CONCLUSION

This paper provided an analytical efficiency comparison of cycling operations with Diesel and Bio-Diesel.

Conditions

were derived that ensured that the efficiency advantages of cycling for Diesel carry over to Bio-Diesel.

It

was shown that in most cases these advantages carry over to Bio-Diesel if the same operating points are used.

However

it is currently not clear, if significant improvements in efficiency are obtainable if the operating points are changed when transitioning to Bio-Diesel.

5. FUTURE RESEARCH

(1)

Changing

operating points to maximally exploit the Bio-Diesel BSFC – How much can be gained?(2) Emission effects of frequent operating point changes(3) Does flattening out of the bsfc curve reduce the benefits of cycling in the case of Bio-Diesel?

THANK YOU!!!