Two-Stroke Software Review - Using Blair's Design & Simulation of Two-Stroke Engines Software

Two-Stroke Software Review

Part 1 - Introduction to Two-Stroke Software

Bimotion v 2.1 - Blair S.A.E. - Dynomation 2 - MOTA v 5.0 - TSR

Using Blair's Design & Simulation of Two-Stroke Engines Software

1989 Blaster Engine Rebuild

Using Blair's Design & Simulation of Two-Stroke Engines Software

To get started the software asks "Are you running the program?"

Program - 1.1 - Piston Position asks for the bore, stroke and connecting rod length. It then asks for the degrees ATDC you want the output data to start from, end at, and the increment of degrees you want it displayed in. I entered the Blaster engine data. From this it calculated the piston position and output the data as degrees of crank-angle ATDC and included the volume above the piston at the various increments I specified. This data output is very simple in nature.

Program 1.2 - Loop Engine Draw is a much more detailed program. It asks for the input data from Program 1.1 but needs additional data including exhaust port opening timing, transfer port opening timing, inlet port timing, trapped compression ratio, squish clearance, wrist pin to piston crown height and wrist pin to skirt distance (both measurements taken from the center of the wrist pin). I entered the Blaster engine data. This program runs a sort of movie of the engine (basic computer animation) - its parameters have been drawn out and the crankshaft goes through one revolution. It shows additional parameters all taken from the crankshaft centerline.

Program 1.3 - QUB Cross Engine Draw is like Program 1.2 but instead uses the data to generate an engine using a deflector type piston. I ran the simulation using the same input data as above but included a 16 mm deflector on the piston top. This is interesting but quite a different piston design than that which is used in the Blaster.

Program 1.4 - Exhaust Gas Analysis, asks for the air to fuel ratio, brake specific fuel consumption, oxygen concentration in the exhaust, carbon monoxide emission, carbon dioxide emission, oxides of nitrogen. The program then ask whether to output the data in hydrocarbon ppm (parts per million) using a NDIR (non-dispersive infrared) devise or a FID (flame ionized detector). To complete the data input you must enter the reading you measured in ppm. The output them displays the brake specific air consumption, the brake specific emission values, the brake specific carbon dioxide value, the brake specific nitrogen oxide value, the brake specific carbon dioxide value, the brake specific oxygen value, the brake specific hydrocarbon value by the chosen hydrocarbon input devise and the trapping efficiency. This program asks for information I could not supply.

The next several programs contain a tremendous amount of information relating to the gas flow through 2 stroke engines. With over 150 pages and several programs dedicated to this topic a great deal of effort has been spent covering it. However it is beyond the scope of this article to cover these programs. Simply put, for most people this section of the book and the programs associated with it are mind boggling, though I may put the software in this section to use later on. Program 2.1 - Wave Flow will let you calculate the velocities of acoustic pressure waves within pipes. Program 2.2 - Superposition will let you calculate the superposition of oppositely moving waves. Program 2.3 - Friction & Heat Transfer will let you calculate the losses due to friction heating during the pressure wave propagation. Program 2.4 - Inflow & Outflow will let you calculate the reflection of pressure waves in pipes for outflow from a cylinder and inflow to a cylinder. Program 2.5 - Three-Way Branch lets you calculate the reflections of pressure waves at branches in a pipe (multiple cylinders).

Program 3.1 - Benson-Brandham Model, 3.2 GPB Scavenging Model, 3.3 QUB Scavenging Model, 3.3a - GPB Cross Ports, 3.3b - QUB Cross Ports, 3.4 Loop Scavenge Design and 3.5 Blown Ports (supercharged) are programs which model cylinder scavenging in each of the different types of 2 stroke engines. The output is data as scavenging ratio, scavenging efficiency and trapping efficiency.

Program 3.4 was used since its data could accept a 5 transfer port loop scavenged design engine. It is a very interesting program which allows port wall considerations to be designed. There are entry inputs for vertical and horizontal port wall dimensions. The output data from this program was generated as main port plan width, side port plan width, total effective port width (TEPW) and total effective width/bore ratio (TEWBR). I input data from the Yamaha engine as measured. The TEPW came out to 96.8. The TEWBR came out to 1.46.

Program 4.1 Squish Velocity is an interesting program that could be very helpful to determine the maximum squish velocity for a typical central dome type cylinder head. I should mention that the stock Blaster uses a combustion chamber shape which is not completely represented by any of the programs relating to cylinder head types - but then again I'm not trying to design a combustion chamber like the stock one. Though all of the programs in chapter 4 will calculate the maximum squish velocity (MSV) from the data input, these programs are very visual in that the results are drawn on the screen so the changes can be easily witnessed in the form of a little animation. Program 4.2 - Hemi-Sphere Chamber is probably the best combustion chamber program in this set for use with this test engine and I used it to calculate the combustion chamber maximum squish velocity. I entered the bore, stroke and connecting rod length (66.5 mm, 57 mm & 110 mm respectively) into the program along with my new exhaust port timing of 88.5 degrees ATDC. I chose a trapped compression ratio of 7.86:1 and a squish area ratio of .55 (.50 for this figure would be 50% of the bore area - .45 would represent 45% of the bore area). I choose a squish clearance of 1.1 mm to keep things safe. The output data computer a maximum squish velocity of 29.2 m/s, a maximum squish pressure of 1.081 which both occurs at 10.5 degrees BTDC. The squished kinetic energy comes out to 9.0 mJ.

Programs 4.3 - Hemi-Flat Chamber, 4.4 - Bathtub Chamber, 4.5 - Total Offset Chamber, 4.6 - Bowl In Piston, 4.7 - QUB Deflector are specific use programs designed to be used with these different types of combustion chambers.

Program 6.1 - Time Area Targets lets you input data to aid in the development of the basic engine design. The program asks for either the target power level from the swept volume at a specific engine RPM, or the target BMEP only, or the target BMEP level from a given swept volume at a specific engine speed. In my case I choose the first option. I entered the target power in kW units (18.6425 is the same as 25 HP), the swept volume of 198 cm^3 at the speed of 8000 RPM. The output showed the engine would need a total exhaust time area of .0124 s/m (124). It then provides two total transfer port time area targets - an upper and a lower value. The upper value is .0070 s/m (70) and the lower value is .0118 (118) s/m. The total inlet time was calculated at .0111 s/m (111).

6.2v2 - Expansion Chamber (will be discussed in a subsequent report).

6.3 - Time-Areas - I entered the data from the Blaster barrel. The program gave me the following information. All data is in mm, degrees and s/m units. The intake ports will have to have their area calculated elsewhere since the data input was for degrees of crankshaft rotation only. In this reed valve engine the inlet ports are always open. There wasn't a way to enter the data of 5 transfer ports that had 3 different widths so I entered them all as 23 mm wide. That's a little on the high side.

Exhaust Port Data@7000

Exhaust Opens ATDC Fully Open @ Number of Ports Width Each Total Area Total Time Area Blowdown*10^4

91.5 170 1 42 889.3 125.8 7.1

Transfer Port Data@7000

Transfers Open ATDC Fully Open @ Number of Ports Width Each Total Area Total Time Area*10^4

119.5 167 5 23 1231.7 122.7

Intake Port Data

Number of Ports Width Each Total Area

2 18 847

The stock engine @ 7000 RPM.

Exhaust Port Data@8000

Exhaust Opens ATDC Fully Open @ Number of Ports Width Each Total Area Total Time Area Blowdown*10^4

91.5 170 1 42 889.3 110.1 6.2

Transfer Port Data@8000

Transfers Open ATDC Fully Open @ Number of Ports Width Each Total Area Total Time Area*10^4

119.5 167 5 23 1231.7 107.3

Intake Port Data

Number of Ports Width Each Total Area

2 18 847

The stock engine @ 8000 RPM.

Exhaust Port Data@8000

Exhaust Opens ATDC Fully Open @ Number of Ports Width Each Total Area Total Time Area Blowdown*10^4

88.5 180 1 43 991.6 125.2 6.6

Transfer Port Data

Transfers Open ATDC Fully Open @ Number of Ports Width Each Total Area Total Time Area*10^4

116.5 180 5 23 1430.4 125.8

Intake Port Data

Number of Ports Width Each Total Area

2 18 847

The Modified Engine @ 8000 RPM.

Note how the changes in the port timing also change the port area and time area. In this case the modified engine shows port time area @ 8000 that's almost the same as the stock engine at 7000 RPM.

6.4 - Reed Valve Design is the program chosen for this engine since the Blaster engine is fitted with a reed valve. By using the data entry parameters as outlined in Part 5 I was able to correctly represent the reed system. The output data showed the required reed area to be 949 mm^2. The actual port area was determined to be 1281 mm^2. The actual reed area is 773 mm^2. The program calculated the size of carburetor that could run through this cage at the specified target RPM as being 34 mm. The reed natural frequency is 145 Hz and the engine natural frequency is 133 Hz. The reed tip ratio is 0.20 and the stop plate radius of 67 mm. It didn't ask me for the actual reed stop plate radius so I wonder if this is an ideal radius for that piece. The change I made in the reed petal thickness from the original .42 mm glass fiber to the .51 mm glass fiber changed the reed natural frequency from 119 Hz to the 145 Hz shown above. In order to have it come close to matching at 8000 RPM (134 Hz) the petal thickness would have to be increased to only .47 mm.

6.5 - Disc Valve Design is not a program that can be used with an engine of this type.

8.1 - Diffusing Silencer and 8.2 - Side-Resonant Silencer may be covered in subsequent reports.

More to come - Rick

Two-Stroke Software Review

Part 1 - Introduction to Two-Stroke Software

Bimotion v 2.1 - Blair S.A.E. - Dynomation 2 - MOTA v 5.0 - TSR

Using Blair's Design & Simulation of Two-Stroke Engines Software

1989 Blaster Engine Rebuild