Combustion Characteristics of HRD/SPK Alternative Diesel Fuels and F-76 Blends in a Marine Diesel Engine

Prof. Knox Millsaps

Visiting Assoc. Prof. Patrick Caton, USNA

Mr. Doug Seivwright

LT John Petersen & LT Adam Paz

Department of Mechanical and Aerospace Engineering

Naval Postgraduate School

ONR Alternative Fuels Meeting, September 26, 2013

Outline

• Diesel Combustion Issues with Synthetic and Biofuels

• Program Objectives

• Experimental Set-up

• Test Matrix

• Analytical Models

• Data Analysis

• Conclusions

Issues with Synthetic and Biofuels

Fleet Demonstrations in 2012 (RIMPAC) and 2016

• Navy procured Hydro-Reformed Diesel (HRD) has high cetane

number (approximately 78)

• Normal cetane range for Navy ship bulk fuel (F-76) is 42 to 67

• Diesel OEMs are “uncomfortable” with such high cetane

numbers

• Other synthetic fuels that have been widely tested in gas

turbines (USAF) such as Synthetic Paraffinic Kerosene (SPK)

have very low cetane numbers (e.g. 25)

• It is not well understood the impact of such wide variations in

cetane number on typical real marine diesel engines

Program Objectives

Experimentally measure the combustion differences in HRD/SPK and blends to quantify potential negative (positive) changes in a real marine Diesel engine

Quantify the changes in performance and mechanical loads/shocks to the engine with low and high cetane syn/bio fuels

Create a kinetic model to capture the ignition behavior (ignition delay) Question: To what extent can a general reference fuel chemistry model capture (predict) ignition behavior of these disparate fuels?

Educate Naval/DoD officers in critical biofuels issues so they will become tomorrows leaders in these technologies

Methodology

Experimentally measure performance over range of fuel blends

HRD/F76: 0/100 25/75 50/50 75/25 100/0

Cetane (46) (56) (66) (72) (78)

SPK/F76: 0/100, 25/75, 50/50, 75/25, 100/0

We thank Dr. Tim Edwards from AFRL/WPAFB for the SPK/data.

46 43.5

37.2

31.6

24.7

20

25

30

35

40

45

50

0 25 50 75 100

Ce

tan

e N

um

be

r

Fuel Blend (% SPK in F-76)

Test Engine and Set Up

Engine Control Console

Detroit Diesel 3-53

Data Acquisition System

Gravimetric Fuel System Fuel Distribution Stand

Engine Specifications and Schematic

Type Direct-injection diesel, 3 cylinder in-line, 2-stroke

Bore x Stroke 98.4 x 114 mm (3.875 x 4.50 in)

Piston-Bore Clearance

0.51 mm (0.020 in)

Speed 550, 1100, 1650, 2200 RPM

Rv 21

Boost 3 kPa – 22 kPa (0.4 – 3.2 psi)

Peak Power 75.3 kW (101 hp) at 2800 RPM

Peak Torque 278 Nm (205 ft-lbf) at 1560 RPM

Intake Air Lab ambient, 22 C

N / T 50 ft-lbf 100 ft-lbf 150 ft-lbf 190 ft-lbf

550 RPM O

1100 RPM O 1 (28 bhp) O

1650 RPM O O O 3 (60 bhp)

2200 RPM O 2 (63 bhp)

Tested Fuel Properties

F-76 HRD SPK

ρ (kg/m3)a 844 778 760

σ (mN/m)b 25.8 24.9 26.8

µ (cSt)c 3.0 2.748 1.088 50:50 Blends

LHV (MJ/kg) 42.7 44.0 44.0 HRD:F76 SPK:F76

Cetane 46† ~75 24.7 ~61 ~35

Composition

Wt% C

Wt% H

Wt% O

Wt%S

% paraffin

% olefin

% aromatic

86.8†

13.1†

0

0.1†

70.7

2.3

27

85.1†

14.9†

0

0†

98.5

0.9

0.6

84.8

15.2

0

0

94.3

4.7

1.0

Properties measured at 15°C (a), 24°C (b), and 40°C (c). Properties measured by Southwest Research Institute, Oct. 2012 and February 2013 or as marked †Naval Air Systems Command, Fuels Division, Patuxent River, MD.

Strain Gage Confirmation of SOI

• SOI timing (nom 10 CAD BTC) varies slightly with speed and load, but not significantly as fuel type is changed. • Allows comparison among fuel types at same speed and load without further characterization of SOI.

Typical Pressure Data

Data Reduction

• Start of Injection (SOI) • Ignition Delay (ID) • Start of Combustion (SOC) • Combustion Phasing (CP) • Combustion Duration (CD) • Maximum Rate of Pressure Rise (MRR) • Peak Pressure (PP)

Relative Ignition Delay For All Points

Relative Metric

X – XF76

(Zero indicates same as F76)

Percent Alt. Fuel in F76

On left, decreasing abscissa is SPK in F76

On right, increasing abscissa is HRD in F76

Cetane number maps from 25 (100% SPK), to 45 (100% F76) , to 75 (100% HRD)

With decreasing [SPK] and increasing [HRD]: • IGD decreases by ~ 1 ms

• IGD decreases more for decreasing [SPK] than for increasing [HRD]

Combustion Phasing and Duration

With decreasing [SPK] and increasing [HRD]: • Increasing combustion duration (less premixed combustion)

• Modest retard in combustion phasing based on 50% burn point (less premixed combustion)

• Very slight change in angle of peak pressure, dependent on operating condition; mostly, retard in phasing offsets decreased IGD, leaving angle of peak pressure unchanged.

gISFC, Peak Pressure, Rise Rate

With decreasing [SPK] and increasing [HRD]: • Decreasing peak pressure (4-6 bar for SPK, 1-2 bar for HRD)

• Decreasing maximum rate of pressure rise (5-10 bar/CAD for SPK, 2-5 bar/CAD for HRD)

• Small increases in gISFC are possible, dependent on operating condition (0 – 5%)

Fuel Chemistry Modeling of IGD

Diesel PRF Mechanism • 4204 species, 20235 rxns • i-C16H34 and n-C16H34 • Sarathy, et al. 2011; Pitz, Westbrook, et al. 2011. What Φ and T? Map of IGD across Φ, T space shows three regimes: 1. T-only dependence 2. T and Φ joint 3. Φ-only dependence

Ignition Delay (ms)

Estimation of Temperature at SOI

Methods (a) Single zone, ideal gas,

measured P, V. (b) 50% of (c). (c) Two-zone; central core ideal gas,

w/o piston boundary layer. (d) Two-zone; central core ideal gas. (e) Isentropic, ideal gas, based on

pressure ratio. (f) Isentropic, ideal gas, based on

compression ratio.

• Estimates are bounded by methods (a) and (e), low 700’s to upper 800’s K.

• Method “C” gives estimates as 797 K – 818 K.

• Is this temperature range important?

Sensitivity of IGD to T and Φ

• Chemistry model shows relatively large effects of Φ, T on (absolute) predicted IGD

• Accurate estimates of T and Φ are critical for absolute accuracy in IGD prediction

• However, trends are similar and converge at high cetane

Red = variation of Φ (1.0, 2.0. 3.0, 4.0) at constant T = 800 K

Blue = variation of T (800 K, 850 K, 900 K, 950 K) at constant Φ (3.0)

Modeling Relative IGD

• PRF mechanism is able to capture relative IGD very well.

• Agreement here is indicative of importance of chemistry in IGD and that differences in spray development between the tested alternative fuels are minimal with respect to IGD

Model (dashed line) corresponds to PRF mechanism at: • P = 50 bar • T = 800 K • Φ = 2

• Successful operation was achieved with mixtures of F-76, algal-HRD (cetane 75+), and SPK (cetane 24.7) across speed-load map.

• Changes in ignition delay cause changes in fuel-air premixing, combustion duration, and phasing; these changes mutually offset for angle of peak pressure.

• Decreasing SPK, higher HRD fuels yield decreased peak pressure, rates of pressure rise, and cause slight increase (0 - 5%) in fuel consumption, dependent on operating condition.

• Higher cetane fuels created less stress and shock on engine. Engine did not run smoothly on 50/50 or higher SPK/F76 blends (37 cetane number).

• Fuel effects are generally monotonic with cetane number.

•TSOI is bounded between ~750 and high 800’s K, but PRF chemistry modeling shows that the uncertainty in TSOI and Φ results in large variations in predicted absolute IGD, while relative trends are similar.

• Using various mixtures of n-C16H34 and i-C16H34, depending on fuel blend, at Φ = 2 and T = 800 K captures experimental relative IGD well, suggesting the primary importance of chemistry effects between these alternative fuels and that similar models could be used to predict relative differences in IGD with other alternative fuels.

Conclusions

• Need better estimate of SFC changes over

torque/speed map - MEP

• Better measurements (Optical) of injection and

combustion. Will start this fall.

• Impact of injection timing, cycle re-optimization for

higher cetane fuels

• Need to understand any emissions impact of HRD

• Can combustion be enhanced by Transient Plasma

Ignition (TPI).

Unresolved Questions

Questions?

NREIP Student

Kyle Reed