PAV: Pressurized Air Vehicle
Midterm Report
MAE435 29785
Michael Parsons
Richard Hartman
Sean Moninger
Aaron Moore
Vincent Constantino
Kyle Curling
Justin Frohock
Amy Hayde
Jacob Kilmurray
Andrew Knepper
Matt Sanford
Contents
List of Figures
Abstract
1. Introduction
2. Background
2.A Gasoline Engines
2.B Compressed Air Engines
2.C Efficiencies and Emissions
3. Methods
3.A Initial Decisions
3.A.1 Engine Choice
3.A.2 Chassis Choice
3.B Compressed Air Engine Theory
3.B.1 Theoretical Engine Calculations
3.B.2 Engine and Vehicle Testing
3.C Engine Modification
3.D Vehicle Integration
3.D.1 Air storage system
3.D.2 Air Pressure Regulator
3.D.3 Supply Lines
3.D.4 Intake Manifold
4. Results
5. Discussion
6. Appendices
6.A Coding
Code A.1 Head Loss in Induction Lines
Code A.2 First Thermodynamic Model
Code A.3 Second Thermodynamic Model
Code A.4 Air Consumption
6.B Project Information
Table B.1 Budget
Figure B.2 Gantt Chart
7. References
List of Figures
Page 2: Figure 1, Four-Stroke [1]
Page 6: Figure 2,Two-Stroke[6]
Page 7: Figure 3, Four-Stroke[3]
Page 10: Figure 4, P-V Diagram
Page 14: Figure 5, Gears[4]
Page 14: Figure 6, Sprockets[5]
Page 15: Figure 7, Welded Lobe[5]
Page 15: Figure 8, CAD of Lobes
Page 16: Figure 9, Induction Mounting
Page 19: Figure 10, Intake Design
Page 20: Figure 11, Intake Safety Factor
Page 25: Code A.1 Head Loss in Induction Lines
Page 26: Code A.2 First Thermodynamic Model
Page 27: Code A.3 Second Thermodynamic Model
Page 28: Code A.4 Air Consumption
Page 29: Table B.1 Budget
Page 30: Figure B.2 Gantt Chart
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Abstract
Carbon dioxide and other greenhouse gasses are a massive problem to a modern society with a massive rate of energy consumption. Many steps are being taken in order to reduce humankind’s rate of greenhouse gas emission, but not all options have been explored. One of the least explored options is the compressed air powered vehicle. Traditional gasoline engines combust gasoline with air, producing a large amount of CO2. Conversely, compressed air engines do not directly produce any CO2 at all, and may therefore be a great solution to emissions issues.
The compressed air engine project involves conversion of an internal combustion engine to run on compressed air. A single cylinder four-stroke motor was chosen alongside the frame from the Mini Baja vehicle primarily due to budgetary limitations. Four methods of converting from four-stroke to two-stroke were determined. An air induction system was also designed completely. An estimation of theoretical power was made along with estimated run time. Currently the project is waiting on fabrication of new cam lobes.
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1.Introduction
Many factors affect the perception of current automotive technology and the increase in research to determine a more efficient means of transportation. Global concern over greenhouse gas (GHG) emissions, smog production, climate change, fossil fuel depletion, and higher gasoline prices during already trying financial times drive automotive companies to produce an efficient and economical passenger vehicle.
In the United States GHG emissions from transportation increased 20 percent between 1990 and 2010. This increase is attributed to a more highway miles driven. The conventional internal combustion engine (ICE) produces carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) during gasoline combustion [7]. Due to this GHG release, the U.S. Environmental Protection Agency (EPA) regulates the quality of gasoline to ensure less smog, by using reformulated gasoline and controlling the amount of sulfur in gasoline, which is known to compromise the emissions controls on cars[8]. The U.S. Department of Transportation (DOT) and the EPA enacted regulations to curtail the damage produced by passenger vehicles in the U.S. by setting standards for the average fuel efficiency of cars and light trucks to 35.5 miles per gallon (mpg), by the model year 2016, which will be raised to 54.5 mpg by 2025. This increase in fuel efficiency will decrease GHG emissions and also reduce the frequency of refueling and the amount spent on gas[9].
In order to meet fuel efficiency standards, automotive companies have increased development of alternatives to the ICE. Vehicle size reduction is a valid development concept, such as those vehicles currently available in Europe; however, these vehicles are not broadly available or welcomed in the sports utility vehicle (SUV) dense United States. Currently the plug in hybrid electric vehicle (PHEV), full electric vehicle (EV), and hybrid electric vehicle (HEV) are the only alternatives to meet increased fuel efficiency needs. There are downfalls associated with each ICE alternative, including expensive batteries, using rare metals with possible toxic disposal issues and deferring the responsibility of GHG emissions to electricity production[10].
Automotive companies such as MDI and Peugeot Citroen are leading the development of vehicles using pressurized air[11]. Advancements in the use of pressurized air could reduce tailpipe emissions, city smog production, and consumer fuel costs, while eliminating the need for corrosive batteries. GHG emissions will be solely dependent on electricity production; therefore, compressed air vehicles will have lower net GHG levels than gasoline engines if electricity is sourced from renewable resources[10]. As pressurized air vehicles have not entered the market, the purpose of this project is to develop a method to convert a gasoline-fueled engine to a pressurized air engine in order to demonstrate the feasibility of utilizing the renewable resource of compressed air for vehicle propulsion.
2.Background
2.A Gasoline Engines
Gasoline engines are a type of internal combustion engine. In an internal combustion engine, a fuel, in this case gasoline, is combusted with an oxidizer to form high temperature gases [12]. These high temperature gases expand and do work to create mechanical energy. There are several types of internal combustion engines, including two-stroke, four-stroke, diesel, and gas turbine engines. Four-stroke engines are the most common of these for small vehicle use.
In a four-stroke engine, the combustion occurs in a cylinder and the high pressure gasses do work on a piston connected to a rotating crankshaft. Each cycle of a four-stroke engine can be broken down into four different parts: the four “strokes,” which can be seen in figure 1.These four parts are induction, compression, power and exhaust. The induction stroke begins at top dead centre (TDC) and ends at bottom dead centre (BDC). During this stroke, an induction valve is opened at the top of the cylinder and a mixture of gasoline and air is drawn into the engine. The compression stroke begins at BDC and ends at TDC. During this stroke, the induction valve is closed and the gasoline/air mixture is compressed as the piston moves to TDC. The power stroke begins at TDC and ends at BDC. During this stroke, the compressed gasoline/air mixture is ignited by a spark at the top of the cylinder, causing combustion, forming carbon dioxide, water vapor and heat[13]. As the gasoline/air mixture burns, the products expand and cool, forcing the cylinder downwards. The exhaust stroke begins at BDC and ends at TDC. During this stroke, an exhaust valve at the top of the cylinder is opened and the exhaust exits the cylinder and the piston moves up[14]. This cycle encompasses two crankshaft rotations.The camshaft is a rod which controls the timing of the induction and exhaust valves in the engine. It is connected to the crankshaft by a set of speed reducing gears or chains, allowing it to turn at half the rate of the crankshaft.
2.B Compressed Air Engines
In order to converta gasoline engine to a compressed-air engine, it is crucial to understand how a compressed-air engine works in relation to its gasoline powered counterpart. The important parts of a compressed-air engine are the compressed air tank, regulator, delivery system, camshaft, valves, and piston cylinder. These parts are either unique to a compressed-air engine or operate differently when powered by compressed air.
The compressed-air tank is the driving force of the engine. It is equivalent to the fuel tank for a gasoline engine, as it is the source of the energy used to move the piston. Unlike gasoline's energy content, which is a constant value per unit volume, the amount of energy available from the compressed air is completely dependent on the pressure at which it is stored. Unfortunately, as flow leaves the tank the pressure within the tank drops. This causes an inconsistent flow into the engine, thus a regulator is crucial to the compressed-air engine.
In order to stabilize the compressed-air engine, a regulator is used. A regulator allows for a controlled pressure of the flow into the engine. The ideal regulator would give a constant pressure and flow rate from the high pressure tank. A constant pressure allows the delivery system and timing of the engine to be designed for just one pressure instead of a constantly changing flow pressure. Without the regulator, the flow rate and pressure levels would be inconsistent and potentially too high, leading to either a failure in engine components or a very short run time.
The delivery system is the next stage of the engine, and the parts incorporated depend on the design. The main components would include the air tubing, a throttle system, and an intake manifold. The throttle system gives the driver control over the power output of the engine by controlling the flow rate of the air into the engine. The tubing and intake manifold serve to deliver the air from the regulator to the piston cylinder(s). If multiple air tanks are used, the manifold must be designed to receive multiple inflows. The length and the diameter of the tubing must be precise in order to reduce pressure losses in the flow.
For a compressed-air engine, the process that drives the engine is vastly different from a gasoline engine. In a gasoline engine, the intake valve stays open just long enough to pull in the air/fuel mixtures. Conversely, the power output of a compressed air engine increases significantly the longer the intake valve is open during the power stroke. For optimal power output from a compressed air engine, the camshaft needs to be modified to create new timing of the intake valve. Unlike gasoline engines, a compressed air engine does not require a compression stroke, since there is no combustion. Therefore the typical four-stroke configuration of gasoline engines is inferior to a two-stroke configuration.
The source of work on the piston is the final difference between the compressed-air engine and a gasoline engine. Instead of a virtually instantaneous combustion and expansion, the piston is moved by the compressed air in two stages. The first stage occursfrom the initial opening of the intake valve, and the second occurs after the valve closes until the end of the power stroke. With the valve open, the air fills the cylinder at a constant pressure, forcing the piston downward. Once the valve is closed, work is generated by expansion of the gas until the full volume of the cylinder is reached. The gas is then expelled in an exhaust stroke and the process is repeated.
2.C Efficiencies and Emissions
It is useful to see comparisons of emissions and efficiencies within different forms of vehicle power. The comparisons have been done between plug-in hybrid electric vehicles (PHEV), full electric vehicles (EV), pressurized air, and gasoline combustion. GHG emissions are a primary concern of the Environmental Protection Agency, as the emissions lead to a reduction in the Earth’s ozone layer, and smog forming over cities.In particular, vehicle emissions are massively important to certain urban cities like Los Angeles, where car emissions are the sole cause of smog. Both of these issues contribute to global warming and are becoming increasingly problematic each year humans continue to pump GHG into the atmosphere. Vehicle efficiency is generally measured in miles travelled per gallon of fuel (MPG). This number must be calculated differently for compressed air cars and all versions of electric vehicles, but is a very good comparison between different vehicle power sources. Though each power system has its own perks,each has disadvantages.
Gasoline combustionis the current standard for personal transportation vehicles, so it is a good comparison for the other propulsion models. In the United States, cars and light trucks account for 61% of the transportation industry emissions[15]. Each gallon of gasoline burned emits 25 pounds of GHG[15]. In particular, the average CO2 emissions per mile for passenger cars is 423 grams/mile, which equals 5.1 metric tons of CO2 per year[16].
Electric vehicles are becoming more popular, as the technology for these vehicles is rapidly advancing. Between PHEV’s EV’s, and HEV’s (Hybrid Electric Vehicles), the consumer has many options to choose from. The main draw to electric vehicles is that they do not depend on gasoline; instead they rely on batteries to store energy for the electric motors. The primary benefit to electric vehicles is that, as long as there is no gasoline engine for range boosting, electric vehicles produce no immediate emissions. They are not true emission free vehicles, since storing the electrical energy typically requires emissions. Most of these vehicles “fill up” at charging stations at the owner’s house or along major highways, thus electric vehicles will have different emissions and efficienciesin different regions. Regions powered predominantly by natural gas and coal, i.e. the midwest region, will have higher EV emissions compared to regions withsignificant renewable energy production, i.e. the northwest region[15]. The CO2 emissions for a PHEV or EV in the Midwest Region averages 290 grams/mile[17]. The amount would be less in the hydropower rich Northwest Region.
The newest member to the powered vehicle lineup is the Compressed Air Car. The concept behind this vehicle is that on board tanks store energy as compressed air, then air then moves a piston which creates mechanical energy that the car uses to drive[18]. An advantage of compressed air for powering cars is that it becomes a zero emissions vehicle, air is entering the engine, and air is exiting the engine. The only emissions that will be happening due to the compressed air car are whatever is used to fill up the onboard tanks: a situation similar to that of electric vehicles. It is important to note that a compressed air engine weighs and costs less than a conventional combustion engine, since the compressed air engine does not require many of the components the gas engine requires, i.e. spark plugs, catalytic converters, and cooling systems. The different options for filling the compressed air tanks include onboard electric compressors that would be plugged in at home or work, or filling locations that have high-pressure compressors. Currently, a major company preparing to sell compressed air cars, MDI, states that their car can be filled up for $2.50 at French electricity prices and can travel 50 miles at full speed on a single tank[18]. While the range of compressed air car is less than that of electric and gasoline variants, the low cost and lack of emissions make for a very competitive vehicle with the increasing costs of petroleum.
3.Methods
3.A Initial Decisions
3.A.1 Engine Choice
Two-stroke and four-stroke engines are the most common forms of gasoline engines available for conversion to compressed air. A two-stroke engine completes the combustion cycle in two piston strokes of the piston, hence the name. Figure 2 is an example of a two-stroke engine configuration.
The primary advantage of selecting a two-stroke engine is that the engine does not have to be retimed since, unlike a four-stroke engine,there are no valves to be operated in a set sequence. A two-stroke engine has fewer moving parts, since it lacks a camshaft and an oil system. In a two-stroke engine, the oil is mixed in with the fuel to lubricate the system. This means that two-stroke engines do not last nearly as long, since the parts of the system wear a lot faster from a lack of a dedicated lubrication system. Another disadvantage is that the intake and exhaust ports must be flipped or sealed up. If flipped, there is a significant loss of efficiency during the compression stroke. If the ports are sealed up, a new exhaust port would need to be designed and implemented, whether it is a slam valve or solenoid. The exhaust port can also be located near the bottom of the piston's travel with the sacrifice of some of the overall efficiency.
The major advantage of a four-stroke engine is its readily available exhaust valve system, as seen in figure 3. The major disadvantage is that the engine must be retimed. This problem extends to the fact that for efficient exhaust discharge, the camshaft would need to be reground. Another solution might be to sacrifice a little bit of efficiency by drilling a hole in the block to discharge some pressure from the engine. Another concern with four-stroke engines is that the engine requires a lubrication system. With the basic lubrication system in place, the engine will produce GHG emissions. By ignoring the lubrication system, the engine will not last very long and the frictional losses will be great.