This paper presents some innovative concepts on an efficient Internal Combustion engine for UAV Applications

1. 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

2. 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

3. 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

4. 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.

5.  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

6. 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,

7. 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)

8. 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.

9. 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
Air Vol. Flow - Cu.Ft/sec. 4.35
Engine Speed - rpm 6000
Engine Speed - Revs/Sec 100.00
No. of Cylinders 4
Air Flow/cyl/sec - cf/sec 1.09
Displacement/rev/cyl 18.79
Total Engine Displ.-cu. In. 75.18
Inlet Port Height - in. 0.40
Cylinder Bore - in. 3.06
Cylinder Area - sq. in. 7.36
Stroke - in. 2.55
Req. Stroke - in. 2.95

10. 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%.

11. 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:
Air Vol. Flow - Cu.Ft/sec. 91.02
Engine Speed - rpm 5000
Engine Speed - Revs/Sec 83.33
No. of Cylinders 12
Air Flow/cyl/sec - cf/sec 15.17
Displacement/rev/cyl 314.57
Total Engine Displ.-cu. In. 3774.83
Inlet Port Height - in. 1.50
Cylinder Bore - in. 7.83
Cylinder Area - sq. in. 48.17
Stroke - in. 6.53
Brake HP per cubic inch 1.88
@ Eq. Ratio = 0.6
Mean Piston Spd. - ft/min 5442

12. Cycle Analysis Results for 7000 BHP Turbo Compound Turbo Fan

13. Summary Table Showing Comparison Between
The Proposed and Product Engines

14. 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.

15. 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.

16. 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.

17. 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.