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Background
Background
This project was done in my Advanced Internal Combustion Engines class. The class had around 15 students in which we collaborated for some parts of the projects. The objective of this project was to design an intake manifold that replicated the performance of an original Nissan Z engine intake manifold. The manifold was meant to fit with a Nissan engine with a Z cylinder head and KA engine block. The engine was converted into a generator. The purpose of converting the engine was to reduce embedded energy that would be needed to manufacture another generator engine. This project follows the mission of REMADE, Reducing Embodied-energy and Decreasing Emissions in Materials Manufacturing, an organization that promotes reducing embodied energy by using current technology that is already fabricated, and utilizing that technology. Below you will find how the project progressed through out the semester.
Valve Analysis
Valve Analysis
The graph to the left displays the lift, velocity, and acceleration of the valves in during one complete cycle of the camshaft. This data was obtained from using a cam degree wheel to obtain valve lift data. Before recording any numbers, valve lash was implemented. Valve lash creates space between valves and the rocker arms that push them down to open the intake or exhaust ports. This is done to prevent constant pressure from the rocker arms on the valves when the engine gets warm. Heat can make the valves expand which would then increase the force that is imposed on them, potentially damaging them.
After lash was made, the lift data was recorded. To obtain velocity and acceleration of the valves, the lift data was placed into Matlab. The data was displayed as a smooth spline in order to get rid of noise on the graph. The derivative of the curve was then taken to obtain velocity, and again to obtain acceleration. If you click next on the presentation, you'll be able to see a table that displays maximum values from the curves in the graph above. Click here to find the Matlab code for this analysis
Mach Index Number
Mach Index Number
Mach Index Number is the ratio of the local velocity of air to the sonic velocity of air going through an inlet. In a general sense, a Mach Index of under 0.5 indicates that an engine has acceptable volumetric efficiency. At above 0.5 Mach Index, the air that goes through the inlet experiences chocked flow in which the air velocity is fast but, the mass flow is reduced. To test for the Mach Index number, we conducted a flow bench test on the Nissan KA engine block. From there we tested the flow through a single inlet valve. We adjusted the height after the end of each test to have a wide range of data to analyze. The numbers we came up with can be found on the table to the top left.
With the data obtained, we used Matlab to conduct a cross plot of the crank shaft angle of the engine and, the flow coefficient through the inlet. The graph of the cross plot can be found on the next slide of the presentation. The average height of the curve told us the average flow coefficient through the inlet. From there we could calculate for the Mach Index Number which was found to be 0.39 which meant that the engine had acceptable volumetric efficiency. Click here to find the Matlab code for this section.
Acoustic Tuning
Acoustic Tuning
Acoustic tuning is meant to get the most out of pulsating waves of air flow. Conflicting air waves can reduce air flow through inlets and in turn reduce volumetric efficiency. For this project though we didn't have to take into account acoustic tuning because of how the generator engine would operate. Usually automotive engines have induction systems that are tuned for around 2,000 to 4,000 rpm however, the generator engine in this project was meant to operate at only 1800 rpm, making acoustic tuning unnecessary. From this point of the project, the objective to designing our manifold will be to keep its costs as low as possible.
Gaseous Mixtures and Volumetric Efficiency
Gaseous Mixtures and Volumetric Efficiency
Our engine used a carburetor to form gaseous mixtures. The venturi effect is used to create pressure drops which forces fuel to be extracted and mixed with air. Venturis are created by varying the cross sectional area at which air flows through. The cross sectional area is reduced to create pressure drops though, there is an advantage and disadvantage on the size of the varying cross section. Smaller areas of flow increase pressure drop to increase the amount of fuel that mixes with the air however, too much of a pressure drop can lead to reduced air flow. The original engine carburetor venturi had a cross section of 20 mm. We also had access to a venturi cross section of 23 mm.
Matlab was used to calculate for the theoretical volumetric efficiency with regard to the carburetor venturis. Which turned out to be 78.54% for the 20 mm venturi, and 81.73% for the 23 mm venturi. Afterwards, we did a flow bench test on the 23 mm cross section to find experimental results of its volumetric efficiency which we found to be 85.85% when air was flowing at 60cfm (cubic feet per minute), and 85.72% at 80 cfm. Though the 23 mm cross section had more efficiency due to a lower pressure drop, the 20 mm cross section still had the advantage of better mixture among the air and fuel. The Matlab code for this section can be found here.
Intake Manifold Design
Intake Manifold Design
The slide presentations on the left show various angles of the initial and final intake manifolds I designed on Solidworks. The manifolds were designed individually by each student. The engine we were working with had an inline four configuration, hence the reason for four holes in the front. The holes were placed in a way to line up directly with the holes of the engine block that the manifold was meant to connect to. Though only one runner can be shown, the initial reason for making the runner curved was so that the manifold wouldn't take up space compared to if the runners were straight. The idea was to create a simple manifold that wouldn't take up substantial space and, would be relatively easy to manufacture however, while working on this design, I quickly realized that it had to be changed.
For the final design, some holes were cut in the front of the manifold. This was done so that the spark plugs on the engine had room to fit in. The smaller holes seen at the front were placed to let through bolts that connect the manifold and engine block together. The runners were made shorter and straight to make the design simpler, and reduce the amount of material required for manufacturing. The plenum at the end of the manifold has a hole at the bottom in the center through which air can flow through. The placement of the hole was meant to minimize as much uneven air distribution as possible. The plenum was shaped to be rectangular to keep the design simple for manufacturing purposes. Since acoustic tuning was neglected, the constraints that affected this project the most were the material choices and, the cost of manufacturing. Overall, the design was made to keep costs low by implementing simple parts that would be easy to cast, mold, or machine.
Cost Analysis
Cost Analysis
After the final design was finished, a cost analysis was conducted to observe which material and method of manufacturing would meet the goal of having each manifold cost under $100 per unit. I looked into materials such as nylon and aluminum. Compared to aluminum, Nylon is a lighter and, has a lower heat transfer coefficient. This would give it the advantage of having colder air flow into the engine. Colder air is denser compared to hotter air which lets it burn more fuel during combustion. I used http://www.custompartnet.com/ to conduct the cost analysis. I based the cost analysis on the material used and, the dimensions of the final intake manifold design. With Nylon and injection molding, the cost per part was well over $100. Even though Nylon is lighter than aluminum, such an advantage is irrelevant due to the fact that the engine would be used as a generator and not an automotive engine. My final analysis utilized the use of Aluminum 356 T6 which has good strength and, is able to withstand environments of high temperature. Using the customparts.net sand-casting calculator, I was able to estimate a cost of $54.09 per part which meets the cost constraint of under $100.
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