Innovative IC Engine Concept

An Innovative Turbo Compound Internal Combustion

Engine Concept for UAV Applications

Jack Taylor

Excel Engines Engineering Company

Dr. Jayesh Mehta

Joe Charneski

Belcan Corporation

Presented at AIAA Propulsion and Energy Conference – 2015

Orlando, Florida

07/27/2015

Agenda

Introduction

Stratification Approaches

Proposed Engine Configuration

Full Expansion – Ideal Cycle

Turbo Charged – Turbo Compound Cycle

Proposed Innovations to Combustor Design

Ideal Cycle Analysis And Pertinent Assumptions

Initial CFD Based In-Cylinder Flow Analysis

Observations and Future Work

Introduction

Inherent shortcomings of conventional petrol and diesel IC engines

Petrol engines exhibit high full power efficiency, but poorer part load characteristics,

Diesel engines have excellent part load characteristics, though poorer full load efficiency,

Both exhibit poor emission characteristics due to high peak temperatures associated with stoichiometric

ignitions, and

They both exhibit significant energy losses through cylinder walls, cylinder head, and through

hot exhaust gases.

Charge Stratification

Provides means to run an engine partway between heterogeneous Charge Ci engine, and homogenous Charge

SI engine,

Objective of this design is to distribute fuel/air mixture from rich to lean across the cylinder, and still maintain

overall lean combustion (Phi ~ 0.6),

Relatively leaner combustion also results into higher thermodynamic efficiency, lower emissions, and lower heat

losses through cylinder walls, where

NOx at full power is lower due to lean combustion, while CO at part load is lower due to reduced quenching in

the thermal boundary layer at the wall.

Approaches to Stratification

(a). Ricardo’s design for primary and auxiliary fuel injection, (b). Rich – Lean Combustion, ©. Rich – Lean Premixed,

(d). Swirl Stratified

IC Engine Efficiency Losses Pathways and Suggested Recovery

Mechanisms

Primary Pathways

1. Losses associated with uncontrolled combustion (e.g. knocking), hot

and cold gas mixing, and largely stoichiometric combustion.

Higher compression ratio, lean combustion, variable fuel injection (rich and lean), and

stratified charge. Compound compression and expansion cycles.

2. Pressure and thermal energy losses in exhaust.

Turbo compounding, multiple stage axial turbines, intercooling, and improved scavenging

through selective exhaust valve timing.

3. Thermal energy losses through walls.

Improved wall materials, TBC coatings, Ceramic Matrix Composites (CMC), lean-stratified

combustion (Lower near wall temperature), and smaller engine with higher density charge

air (Super charge-intercooler combination).

Secondary Pathways

1. Pressure losses associated with flow path, air/gas mixing, etc.

Improved turbo and compressor systems, and robust air flow management for flow through combustor.

2. Mechanical friction, and other parasitic losses.

Better low friction lubes for piston and rings, reduced shaft work to drive auxiliaries, and

lean burn yielding low NOx, with attendant lower burden on after-treatment.

Ricardo Design:

Fuel is injected through two fuel nozzles. The auxiliary fuel nozzle

injects spray directed at the igniter. The fuel/air mixture is near

stoichiometric for this stage. Next, a cylinder head mounted

injector sprays fuel directly into the cylinder. The overall combustion

occurs at relatively leaner mixture.

Due to rich burning during ignition, this arrangement gives better

performance at higher speeds.

In this version auxiliary rich fuel air mixture is ignited

Using a spark plug,

Main lean fuel air premixed mixture is Introduced in the

cylinder for a complete lean Combustion.

Stratified Charge

In another version, rich stoichiometric fuel is introduced

near the spark plug over the full load range. Away

from the spark plug the fuel air mixture is lean with

nearly pure air within the wall boundary layer.

Swirl Stratification

Current Uni flow, two-stroke Swirl

Stratified Design

In the proposed design, swirl is introduced at the

Intake through angled intake ports.

The angle of the ports, angular jet momentum,

etc. to be optimized.

Two-Stroke Uni flow configuration,

Stratification achieved through swirl and affecting near

stoichiometric combustion at the spark plug,

Full Expansion Engine

Base line IC Engine Concept:

Introduction of CMC or high temperature TBC on combustor walls and piston,

Longer power stroke compared to compression stroke in order to

minimize exhaust energy losses. This is achieved via leaving exhaust valve open

For part of compression stroke,

Lean combustion, phi = 0.6,

Exhaust valve pressure ratio – near two,

Fuel injected in the vicinity of the spark plug, rich combustion at the spark plug

where leaner fuel air mixture radially away from the spark plug,

Highly swirled flow, high turbulence, and intense mixing at the top of the compression

stroke, and

Applications in auto vehicles.

Performance improvements through turbo compounding

Introduction of an intercooler to reduce compression work,

Introduction of multi stage turbine for increased power output, and

Applications in turbo prop and turbo fan configurations. (500 HP, and 7000 HP UAV)

Full Expansion In-Cylinder Combustion

An Idealized Cycle Analysis – A 100 BHP Machine

Air Vol. Flow - Cu.Ft/sec. 2.22

Engine Speed - rpm 5000

Engine Speed - Revs/Sec 83.33

No. of Cylinders 2

Air Flow/cyl/sec - cf/sec 1.11

Displacement/rev/cyl 46.02

Total Engine Displ.-cu. In. 92.04

Inlet Port Height - in. 0.40

Stroke to Bore Ratio 1.00

Cylinder Bore - in. 3.88

Cylinder Area - sq. in. 11.84

Cylinder Stroke - in. 3.89

Req. Stroke - in. 4.29

Engine Expansion Ratio 2.0

Engine Compression Ratio 22

No intercooler

Wall Heat Losses – 5%

Over all Cycle Efficiency

30.3% to 52%

Combustor Pressure

2210 to 3910 psi.

Proposed Turbo Charged Turbo Compound IC Engine

Two-Stroke, Four Cylinder Application – Salient Features

Turbo compressor and the air cooler Increase pressure

and density of the IC Engine intake air,

Swirled intake air introduced into the engine cylinder, burned

and Exhausted into turbo HP turbine,

Gear box coupled with engine shaft Drive slow power, low

speed power Turbine,

Engine/power shaft also drives a Propeller system of the

turbo prop platform.

The proposed configuration offers flex-fuel Capability, higher

overall engine efficiency, High altitude flight capability,

and large turn down in engine speeds.

Engine Displacement and Dimensions:

500 hp Turbo Compound Engine




No. of Cylinders 4







Stroke - in. 2.55

Req. Stroke - in. 2.95

Cycle Analysis Results for 500 BHP Turbo Compound Engine

Centrifugal Compressor:

PR – 4, Efficiency 80%, Intercooler Eff. – 0.60,

Gama – 1.37, Cp = 0.24, Cv = 0.19

IC Engine:

Gamma – f(T),

Gas Turbine:

Gamma – 1.34, Turbine Efficiency – 85%,

Cp = 0.25

Engine Specifics:

Cycle Efficiency – 28.1% to 43.4%,

Indicated HP – 101 to 783

(Nominal – 494 HP at

Phi=0.6, Brake efficiency 23.8% to 42.6%.

Proposed Turbo Charged Turbo Compound IC Engine

Two-Stroke, Twelve to fifteen Cylinder Application – 7000 BHP Machine

Evaluated for SFC at different power conditions,

Evaluated for power generation as a function of altitude,

sea level to up to 70,000 ft.

High power allows use of multiple turbine stages – large

turbine expansion ratio possible.

Direct injection and stratified charge allows engine

power output to be controlled by fuel flow. Reduced

pressure losses through restrictions in the flow intake circuit.

In general design can be scaled up or down with power

requirements.

Engine Displacement and Dimensions:




No. of Cylinders 12







Stroke - in. 6.53

Brake HP per cubic inch 1.88

@ Eq. Ratio = 0.6

Mean Piston Spd. - ft/min 5442

Cycle Analysis Results for 7000 BHP Turbo Compound Turbo Fan

Summary Table Showing Comparison Between

The Proposed and Product Engines

Initial Flow Studies

CFD simulation of the transient flow inside the combustor initiated using FLUENT/GAMBIT

Standard two equation k-epsilon, fast chemistry, and moving mesh feature of the FLUENT

incorporated

TET cells in the remeshing zone, and HEX cells in the dynamic – layering zone

Default, Rossin-Rammler Spray Model, adiabatic walls, etc.

Scavenge Process through Exhaust Stroke

In order to cause effective scavenge, exhaust valve remains open

about 10 deg. Past the BDC (180 Deg.)

At 190 Deg. EV and IV both are open and combustion air allowed in

until about 220 Deg. This helps push out combusted material out of the

combustion chamber

Past 220 Deg. The EV is closed with the compression stroke continuing through

about 10 Deg. Past TDC.

Details of Swirl Stratified Combustion

Fuel injected at 340 Deg. Prior to TDC – in the direction of the swirl,

Fuel evaporation as the fuel moves away from the injection point.

Ignition at 360 Deg., and radial temperature stratification.

Conclusions

A novel IC engine concept is currently being developed that features the following:

Swirl augmented, lean, non-premixed combustion,

Optimized crank travel that offers more efficient scavenging,

Advanced fuel nozzle that injects fuel near igniter. This facilitates improved Vaporization/atomization

resulting in better performance. It also facilitates Flexi-fuel capability,

CMC or high temperature TBC coated walls, piston head, and crown. Results

In lower heat losses,

Uni flow, two-stroke configuration with pressure lube, and

Turbo compounding with a compressor, air cooler, and possibly multiple stages of turbine.

Several applications possible. For example, 100 HP non-turbo could be for automotive/truck application, While

500 HP turbo prop could power a small helicopter.

However, the application envisioned here is for a 7000 HP UAV platform as the proposed compound turbo fan

Offers low SFC (0.285), high altitude capability (up to 70,000 ft) due to compressor and an intercooler, and

Near full expansion thru’ the use of a multi stage turbine.

Innovative IC Engine Concept

Engineering

Transcript of Innovative IC Engine Concept