First of all I would like to mention a very good book, but in particular the book of Kevin L.Hoag; Vehicular Engine Design. It's a small book but very useful in the initial engine's design.
This part will concentrate on the engineering aspects of the engine. Off course the treatment of all the engineering stuff will make this page too elaborate, and therefore I will then refer to the report 'Preliminary design of a six stroke engine' I wrote last year. My apologies for the 'reporting style' of this page, but in the hurry of creating this website, I took the privilege to 'copy' quite a lot.
This is a small summary of the aspects treated in this report;
Power estimation
Fundamental to engine performance is the relationship between work and power. The work or the useful energy output of the engine is generally referred to as the torque output. The power is simply the product of engine torque and shaft speed.
It should be known that for the application of the engine, the shell eco marathon car, one should have a high as possible torque at the lowest shaft speed as possible. This is mainly because of the fact that high engine-speeds immediately mean higher fuel consumption because of incomplete combustion, but also it means that every part has to be very accurately balanced in order to not suffer to much from vibration. At this is an experimental engine; one should try to keep the maximum rev. within certain limits. Therefore a self-imposed regulation will be that maximum torque will be delivered between 2500-3500 rpm, and that the engine rev.limit will be at 5000 rpm. This will result in an engine power-map that will look something like this;
For normal gasoline fuelled combustion engines the air to fuel ratio is around 14.7. This is the value at witch the fuel mixes chemically very good with the air, and is a good average between power and emissions, and is a proven number witch is implicated in most passenger cars. If one looks for more power, but then also more fuel consumption, one should lower the number to 12.0 or even less. Higher air to fuel ratio numbers will imply that there will be so-called lean burning, witch cause under-lubrication of the engine but better fuel economy
Engine displacement
The goal is to design a new spark-ignition engine for an low-performance application. On the 2006 shell eco marathon, the Eco-Runner car drove on a 31cc 4stroke engine from Honda. The engine performed very well and therefore as the application stays the same, one should look to have almost the same engine displacement.
Based to some little dynamics calculations; the engine is to have a rated power of 0.75 kW at 3000rpm. A literature study has suggested that the specific fuel consumption vs. rated power will be approximately 300g/(kWh). Also a volumetric efficiency of 86% at nominal speed will be assumed. This is the factor between the real filling of the cylinder with fuelled air, and the cylinder volume. The number is based on statistics. The estimated displacement is calculated for these assumptions as;
Number of cylinders
As the number of cylinders is crucial to the engine design, it should be well taught. Of course one should try to keep the number of cylinders as low as possible, because of the number of rotating, and thus suffering, parts. But in with the application of steam, one should also remember that the more cylinders, the more surface is coming in contact with the combustion process, witch will generate a heat exchange with the cylinder wall. This is numbered in the Surface-to-volume ratio. It refers to the ratio between the combustion chamber surface area to combustion chamber volume. Of course this number changes as cylinder volume changes throughout the operating cycle. It is of greatest importance near TDC when energy is rapidly released during combustion and heat rejection to the combustion chamber walls is to be minimized.
The only solution left is the use of one cylinder, both in the theoretical an the practical way.
Bore to stroke ratio
Once the number of cylinders has been determined the final remaining basic layout question is that of the bore-to-stroke ratio. While the surface-to-volume ratio is nearly independent at the BDC volume, it is highly dependent on the bore-to-stroke ratio at the TDC cylinder volume. For the same cylinder displacement, a larger bore, shorter stroke engine has a higher surface-to-volume ratio and thus a greater heat rejection into the cylinder wall or cooling system.
Next parameter to consider is the piston speed. For a given desired engine speed, as the stroke is made longer, the piston must travel further during each stroke, and thus move faster. This increases friction, wear and inertia forces.
Another consideration is that of the combustion chamber aspect ratio. In a spark-ignition engine, the challenge is one of flam travel length, the distance the flame must travel as it traverses from the spark plug across the cylinder increases with increasing bore diameter. This can be arranged by either going to small bores or using two spark-plugs. Trade-offs associated with these three parameters just described are presented for a given engine in fig.3
The bore must be made large enough in order to keep the main piston speed below its design target, and in order to make the pressure drop across the valves as small as possible (it sharply increases as the valve diameter goes down).
As general rule the bore is made no larger than necessary to fulfil these two requirements.
Compression ratio
The compression ratio maybe the most important engine parameter for our design. As engine compression ratio is defined as the volumetric rapport between the engine volume and the combustion chamber.
is directly linked to the engine efficiency.
If efficiency is defined as 
,
then one can derive that the efficiency is 
.
For example, if the compression ratio would go from 9 to 10, with 
, then the efficiency would go from 0.48 to 0.50
Of course one would like to raise the compression ratio as high as possible, but this will cause ‘pinging’, which is the uncontrolled self-ignition of the fuel mixture. Pinging or knocking is the self-ignition of the mixture, and can be counteracted by lowering the pressure. This can be done at lower engine temperature, lower compression ratio or taking a higher-octane fuel.
Of course the designer would like to go as high as possible with the compression ratio, and therefore the engine will be designed with a compression ratio of 9, with the possibility to change this number by adding ‘shims’ on the underside of the cylinder. As knocking is dangerous for the engine, a sensor will be placed on top of the engine in order to recognise as fast as possible the typical vibrations, which can lead to complete destruction of the piston and cylinder head.
Basic thermodynamics
From the most books about engines, one can take the basic thermo dynamical formulas and use them. From thermodynamics course one knows that the theoretical engine cycle can be seen as a Carnot cycle.
Doing some little calculations without going in the deep of thermodynamics gives the following results;
Assume;
- - Cv of mixture is 950J/Kg.K
- -
- - Compression ratio=9
Then one can see for
- 1.
2. 
- 3.
(empirical relations) - 4.
Assumptions
For the design of this engine some assumptions have been made in order to be able to use existing knowledge and components.
As piston production requires special tooling and material, one should opt for a standard piston in the range required. In the design of the engine, the authors choose a 33mm piston from Honda used in very small four-stroke applications. This choice has been made mainly because of the fact that it is one of the smallest diameters of pistons, which are easily available, and because of the good previous experience with small Honda engines. Research at Honda revealed that the maximum piston speed is around 10.8m/s witch should be kept in mind when determining the stroke. The stroke is dependent on the crankshaft and has been determined do be 40mm. If can be seen in the formula below that using a 40mm stroke, the engine meets the displacement requirements.
Block layout and design
The engines block is maybe the most complex part of the whole assembly, as it must support many different forces and still be as light as possible, fulfilling the requirements concerning the lubrication and sealing of the different components. The main requirement of the block consists of the supporting of the crankshaft and cylinder. It must contain the main crank bearings and support faces for the cylinder. As the part would probably be CNC machined, a lot of details have already been incorporated, in order to make the whole part as multifunctional as possible. Examples of this are the starter-supports, and clutch-mountings. Logically both sides of the block aren’t symmetrical, but inside the engine they are almost both the same.
The block has been designed in two parts as it should be easily assembled. Between these parts, a small gasket will be put in order to prevent any leakage.
At the underside of the block one can see a small collection basin for the sprayed oil.
Cylinder head design
In ignition engines fuelled with high-octane liquid fuels, a relatively uniform mixture of air and fuel is ignited with a high-energy electrical spark to initiate the combustion process. A flame front then progresses every direction from the spark plug until all of the mixture has been burned. The rate at which the flame front travels, and hence the rate of energy release is critical to engine efficiency. Key parameters in determining the energy release rate are the location of the spark plug, and the distance from that location to each location in the combustion chamber walls.
Because of choosing a very small bore, the packaging of sparkplugs and valves has to be well thought. In the first approach, two sparkplugs will be installed, in order to have a very good flame front, but afterwards, one of the sparkplugs can be changed with the water injector. A first sketch could look like fig6;
It can easily been seen that the determining factors in the design of the cylinder head will be;
-Diameter of sparkplugs
-Diameter of valves-valve seats
-Bore diameter
-Angle of placement.
Sparkplugs
In order to have an easier packaging design, the smallest spark plugs available for small engine applications have been bought, wherefrom the author has made an cad-drawing in order to afterwards being able to do the cylinder head design.
Valve design
The basic features of the poppet valve assembly are shown in fig7.
The valve itself consists of two sections. The valve head is the portion that seals the combustion chamber; it is typically constructed of steel selected for high-temperature strength and hardness. In most engines a high-hardness seat is pressed into the cylinder head beneath each valve. The seat is made of an alloy similar to that of the valve heat and is used to minimize wear resulting form the impact loads seen at valve closure. The valve stem glides in a valve guide pressed into the head. The valve assembly is completed with a valve spring, retainer and keepers as shown in the picture.
The output of the engine at any given speed is a direct function of volumetric efficiency. Of course volumetric efficiency is to be maximized by maximizing the available intake and exhaust flow area. This can be done by;
- using high diameter valves
- higher number of valves
- opening the valve deeper in the cylinder chamber (valve lift)
- making the opening time longer
In the case of this small engine, and considering the already existing packaging problems, one should chose to have only one intake and one exhaust valve.
Another issue, which also needs to be considered at the moment of design, is the ratio between intake flow area and exhaust flow area. At first one may say that the intake and exhaust area should be equal since the same mass must go out as that is coming in, but different factors modify this answer.
Without coming into to deep considerations, it comes to the fact that the mass flow through each valve is driven by the pressure ratio across the valve at any instants in time, and the fact that the specific volume of the exhaust gas is much higher than that of the intake charge, thus requiring greater flow area for an equivalent mass flow rate. A literature study implies that the ratio should be around 1.1 to 1.2.
The valve seating angle is an important flow parameter which has to be considered at the begin of the design. Seat angles range form 15 to 45 degrees. The shallower seat angle allows the effective flow area to increase more rapidly the valve initially lifts form the seat, and it reduces wear due to impact loads.
However, the shallower seat angle typically increases flow separation as lift is increased and makes sealing more difficult. Higher seat angles are generally more advantageous unless valve and seat wear rates become too high. Angles above 45 degrees are not used as these results in valve sticking in the closed position and increase the required opening force. Considering what is said before, and also thinking about production issues, one should opt for a design using seat angles of 45
After some questioning, bronze has been chosen as the valve seat material. Bronze has the nice and useful ability to be self-lubricating and is also again a soft material, which will allow the valve speed to be increased, as impact load will partly be dissipated in the material. As engine endurance is not a real issue for this experimental engine, the rapid wear of the bronze material will have to be monitored, but normally the valve seats will experience the whole engine lifetime.
Valve airflow calculation
The performance of the engine is sensitive to the effective flow area available at any crank angle position during the intake and exhaust processes. The effective flow area is in turn dependent on the combination of valve lift versus crank angle and flow area versus lift. The valve lift versus crank angle is determined by the camshaft lobe design and valve train capabilities.
The flow optimisation begins at the interface between the valve an seat (see previously).
As stated before, the engines efficiency depends on the volumetric efficiency, and thus on the timing and opening area of the valves. At a certain moment, further opening of the valve won’t have any sense, as the main flow area won’t change any more. The valve ‘stem’ which is still in the flow, and can’t be removed causes this. An easy calculation of this depth can be made by;
And then the depth L at which the flow area won’t change any more can be determined to be;
Statistically seen something around this value was expected as general rule of thumb is 
and our diameter is 14mm.
As can be seen in literature, the timing the valves are opened is quite standard for modern engines and have been determined around the following angles;
addendum;
Some small additional part here were the valve motion's speed was determined using the radius of the curvature. Different cams were designed with different openingspeeds for the valves. An optimum was found in this picture, where the maximum opening would be 4 mm and the maximum retraction speed of 60m/s
Camshaft and camshaft holders
As one can imagine, logically the camshafts or at least the cams should be in line with the valves. In normal automotive engines, these camshafts are rotating in so called hydrodynamic bearings. These bearings are the one who will determine engine life, as these are very sensitive to wear when the engine is cold started. Again some gain can be made here using ceramic roller bearings. Something which is also important is the clearance between the cams and the valve (valve head). When the clearance is to small, the valve will come in constant contact with the cam by the fact of heating up and increase, causing a constant small gap between the valve and the valve seat. This will allow cylinder mixture to escape and is called valve burning. When the clearance is to big, a precise prediction of valve opening time is not possible, although the valve will close perfectly in normal conditions. A second advantage of to many clearance in our case, is the fact that the cam will not be in contact with the valve head when not needed, causing less friction and thus a better efficiency again. This clearance can be adjusted using a ‘variable shim’.
The principle is very simple, as one makes different shims with always some very small increase or decrease in thickness. When placing these shims, one can accurately adjust the clearance of the camshafts.
The camshaft holder was a part of big concerns, as it is constantly loaded with sinusoidal loads, it is susceptible to fatigue. In a first small design, the holder looked like this in figure
This design was controlled on nominal stresses using FEM analysis, and was made acceptable for aluminium. At a verification meeting the remark was made that the highly stressed part had to sustain at least 10^5 cycles, which it would never attain using aluminium, as aluminium is very sensitive to fatigue. Two possibilities where opened in order the increase the efficiency of the design;
- Using an other material
- Changing the design
Both options can be good solutions as they have both many advantages.
When one uses steel and the internal stresses do not exceed a certain limit, it can be seen on a so called S-N curve that steel will sustain fatigue to eternity. An S-N curve shows the properties of a material when load with N cycles at a certain maximum stress amplitude S. From this curve one can also see that aluminium doesn’t have such a limit. When making a little investigation on both the options, one can see that the steel part will be much heavier than the aluminium part. This is caused by the fact that both parts have to be redesigned, but the steel part is not fully stressed, as it has to stay a way below its maximum allowable stress. This will then result in an aluminium part looking like
In order to have accurate valve timing, most engines work with chains, connecting the crankshaft and the camshaft. In our design, a chain would be to heavy, and give few possibilities to adjust further the opening angles. Therefore the designer has chose to use a very small pitch timing belt, resulting in a system as shown below. This system has also the advantage of being able to convert from 4-stroke to 6-stroke
Cylinder design
The cylinder has as main function; driving the piston in a lineary motion driven by the explosion.
As the cylinder is not a real high stressed part, it can be made of some aluminum or magnesium like material. The choice for aluminum or magnesium is also justified by the fact that temperature rise in the combustion chamber will never be to high in order to start some melting process.
As the piston is a fast moving object within the engine, it will cause a lot of friction when not proper designed. In order to avoid losses at friction different measures can be taken;
- Lubrication can be applied
- Cylinder wall finishing must be as smooth as possible
As the whole engine has to be as light as possible, again weight gain can be done on the cylinder using aluminum or magnesium. As both materials are to soft to sustain long friction by the piston motion, one should apply a coating in order to ‘harden’ the ‘motion guiding’ surface.
Therefore contact has been made with a specialized company, witch will apply a ceramic coating on the preliminary machined cylinder, which then will be honed to the right diameter. Honing is a process where the cylinder surface is finished to a very fine surface roughness and to a very precise diameter.
As the cylinder mantel is the main heat resource for the vaporization of the water to steam, it should be kept as warm as possible. This could be done by using a heating system directly derived from a normal engine’s cooling system. In order to keep it warm, water that has flown around the exhaust will flow around the cylinder to keep the mantle as warm as possible. As the engine has to be as modular as possible, the engine’s cylinder has to be a ‘stand alone’ part, meaning that it should be mounted on the block, and fulfilling all it’s requirements without being dependent of other parts.
Therefore the cylinder has been split in two parts which will be pressed the one in the other. This is done in order of being able to produce the inside cylinder part or the bushing including the water-cannels. Then the outside part will be pressed over it to close those canals and being the mounting connection to the block and cylinder head.
Manifold design
On the intake side of the engine air and fuel are mixed together and their flow to the cylinder is regulated. Several different components must work together for the intake system to perform these tasks successfully. The main components of the intake manifold include the air filter; throttle body, plenum, fuel injector, and runner. The air filter removes impurities in the air so it will not hinder the combustion process. The throttle body provides the ability to manage the flow of air into the engine itself, increasing the opening to supply more air. The plenum serves as a reservoir for the incoming air to be pulled from when the cylinder requires a charge of air. Fuel can be regulated and mixed with the air through a number of methods from carburetion to electronic fuel injection into the port. Then finally the air flows through the runner and into the engine where it is combusted.
First of all a smooth laminar flow is wanted in areas of the intake where no fuel is present. This will minimize the losses due to wall friction and bends in the manifold system. When fuel is introduced into the system it is necessary for the flow to become turbulent. This will increase the flow velocity and at the same time increasing the atomization of the fuel air mixture to create a proper burn once in the combustion chamber.
The Main goal behind tuning an intake manifold is to increase the volumetric efficiency of the engine. The volumetric efficiency takes into account the losses throughout the system from the air filter to the intake valves themselves. Volumetric efficiency is also not constant, as it depends on engine speeds, and valve opening time, caused by reflection waves.
The length of such a pipe can be calculated using the knowledge that the expansion wave created at the opening of the intake valve will travel trough the manifold till it reaches an ‘infinite opening’. There it will be reflected and come back as a compression wave. Ideally this compression wave is at the valve when it is closing, causing some bit more compression of air and thus a better volumetric efficiency.
Using the formula one can find the ideal pipe length for a certain engine speed. 
where
a = speed of sound
v= speed of flow in manifold
t= opening time of the intake valve
Assuming an engine speed of 3600 RPM, this would lead to an intake length of 88cm. Of course this is to long, and as waves will continue bouncing, this length can be divided by two or four.
At a higher rpm the longer pipes will actually hinder the efficiency of the engine leading to a poor performance curve.
Ambient air first enters the intake system through the air filter. The air filter is necessary because small bits of debris can ruin the tight tolerances inside the engine. The filter should effectively and efficiently remove intolerable particles from the entering air stream while creating as little pressure drop as possible.
The next component is the throttle, which comes between the filter the plenum.
Using air flow calculations, on can find that a throttle diameter of around 12mm is very good. After the throttle the air then flows into the plenum.
The plenum acts to smooth out turbulence in the flow and assure that always unrestricted air is available for the runner. After some internet research and statistical evaluation it was decided that a plenum volume of twice the displacement of the engine should be achieved.
Connecting rod design
The engine simultaneously experiences a variety of internal forces. First, at each cylinder some portion of the crankshaft and connecting rod must be centered at some distance away from the crankshaft centerline as determined by the engine’s stroke. As the crankshaft spins this mass gives rise to a centrifugal force of a magnitude dependent on engine speed and acting outward from the crankshaft at each instant in time. What the engine “sees” is the instantaneous summation of the forces and calculations will be facilitated by recognizing the powerful tool of superposition. The reciprocating-piston engine operates on the kinematic principles of converting reciprocating motion at the piston to rotating motion at the crankshaft. The conversion occurs across the connecting rod with everything connected at its small end experiencing purely reciprocating motion, and everything at its large end experiencing purely rotational motion. The connecting rod itself experiences complex motion that would be extremely difficult to model and calculate. Fortunately such calculations are not necessary as for experimental engines a close approximation can be achieved by simply weighing each end of the connecting rod and splitting the mass between that in the reciprocating and that in rotating motion.
As for the design of this experimental engine we have taken a standard crankshaft, the connecting rod has to meet certain properties in order to be valid for the available counterweight.
Doing measurements on the original connecting rod, one can see that the weights can be determined to be;
Weight on reciprocating side |
32gr |
Weight on rotating side |
28gr |
Position of center of gravity |
35.6mm |
Total weight |
63gr |
Original connecting rod
Of course the new connecting rod should have the same weight on rotating side, and have the same center of gravity in order to prevent vibrations. Using cad models one can work to a feasible connection rod.
A second improvement made on the connecting rod, is the believe of the designer that a small connecting rod is less efficient than a long one, for the same bore to stroke ratio. When the crankshaft is turned 90 degrees, the connecting rod will be at the biggest angle in comparison with the vertical axis. As forces trough the connecting rod can be split between the vertical and the horizontal component, the longer the connecting rod, the smaller the angle, the bigger the vertical component causing the rotation of the crankshaft. Of course this has as negative effect that the engines height will be increased, but in our design this isn’t really a restriction. This again will be an efficiency gain.
Now also a check has to be made on the strength of the design, as the connecting rod is one of the most (if not the most) stressed parts of the engine, some finite element analysis of the part has been done, from where adaptations have been made in order to counter act the stress concentrations occurring while loaded.
FEM analysis of new longer connecting rod
Resulting from the FEM analysis one can see that the maximum occurring stresses are in the order of 300MPa, which is almost the half of the strength which is specified for normal steel. One could opt to use a lighter material or some changes in the design, but as constrains are present resulting from minimal mass at the rotating side, this can’t be achieved.
Fuel injection and control
The whole meaning of this engine is about efficiency, and thus the fuel consumption is very important. From the first engines on, carburetors where used for mixing the air with the fuel, after this called the mixture. The mixture was then compressed in the combustion chamber and ignited by an electro-mechanical ignition.
In the late seventies, cars appeared with electronic injection, not necessarily causing higher performance, but better fuel economy by accurate timing of the injection and better atomization of the fuel. Carburetors had the disadvantage that the long way the mixture had to travel till the combustion chamber was causing condensing of the fuel on the runner and inlet manifold walls and therefore less accurate mixture prediction.
The main advantage of EFI is the fact that it can vaporize the fuel very close to the combustion chamber, and give the opportunity to predict very accurately the mixture properties. When linking an oxygen sensor in the exhaust to measure the completeness of the combustion, one can also iterate with the injector and increase or decrease the amount of fuel injected.
Some basic calculations can be made in order to predict the amount of fuel required for the engine (this is some repetition of the calculations performed in chapter 3, but now specific for injector calculation).
The ideal gas (which air is reasonably close to) obeys the relationship:
PV = nRT
In order to know how much fuel to inject, we need to know how much air is going into the engine so the chemically correct mixture (called “stoichiometric”) can be achieved. For a fuel injected engine, it is required to use sensors to determine the pressure in the intake manifold and the air temperature. However, the temperature in this equation is “absolute temperature” measured in Kelvin which is equal to degrees Celsius + 273º.The volumetric efficiency is a percentage that tells us the pressure inside the cylinder at BTC versus the pressure in the manifold. We know the volume of the displacement of the engine. Thus we can calculate the mass of air in the cylinder using;
P = VE * MAP (i.e. the pressure in the cylinder in kPa),
V = CYL_DISP = the displacement of one cylinder (in liters),
R = 8.3143510 J/mol K,
Since we now know the amount of air in a cylinder from the MAP and IAT(intake air temperature) values and the 'tuned' value for VE, we need to know the amount of fuel to inject. The required fuel determines the length of time in milliseconds [ms] that the system should “squirt” to give the stoichiometric amount of fuel (14.7 Air/Fuel Ratio for gasoline) at 100% VE, a manifold absolute pressure (MAP) of 100kPa, and an air temperature of 15 degrees Celsius for a complete stroke cycle.
The air/fuel ratio (AFR) is the mass of air compared to the mass of fuel entering the engine, so for a 14.7:1 AFR we have 14.7 times as much air as fuel. The volume ratio is much more extreme, about 9000:1, and varies considerably with temperature, so AFR is always specified by mass. A stoichiometric mixture is chemically correct for complete burning with no extra fuel or air left over. For gasoline, a 14.7:1 AFR is considered the correct amount for burning with no leftover air or fuel. Of course in this design we are going to try tho make this air/fuel ratio as high as possible without risking the engine to ‘dry’. This means that the amount of fuel is so low, it will not lubricate the cylinder wall any more.
As the amount of fuel the designer would like to inject is so low, no standard injectors exist which have openings that are small enough to still have the time to control the flow. A special injector was purchased at Bosch.
Injector model
As the flow rating of the injector is known in kg/min, one can determine the opening time required by using different calculators on the internet.
Spark ignition
As seen before the dependency of the engine’s efficiency is only a matter of the volumetric efficiency of the engine. Now when the compression stroke is a fact, in an normal engine a sparkplug would ignite the mixture, causing high pressure increase and therefore the piston to go down creating the work-stroke.
The creation and the timing of the spark is done by the ECU and a transformer. The essential task of firing the sparkplugs to ignite a gasoline-air mixture is carried out by a process which uses Faraday’s law.
Basic spark ignition
The primary winding of the ignition coil is wound with a small number of turns and has a small resistance. Applying the battery to this coil causes a DC current to flow. The secondary coil has a much larger number of turns and therefore acts as a step-up transformer. But instead of operating on AC voltages, this coil is designed to produce a large voltage spike when the current in the primary coil is interrupted. Since the induced secondary voltage is proportional to the rate of change of the magnetic field through it, opening a switch quickly in the primary circuit to drop the current to zero will generate a large voltage in the secondary coil according to Faraday's Law. The large voltage causes a spark across the gap of the sparkplug to ignite the fuel mixture. For many years, this interruption of the primary current was accomplished by mechanically opening a contact called the "points”.
As the efficiency depends completely of the volumetric efficiency, the timing at which the spark ignites the mixture is critical. In a mechanical circuit the time a voltage has to flow trough the wires is constant. Therefore causing later ignition at higher engine rpm, and maybe to early ignition at low rpm and thus terrible efficiency losses.
In order to improve this, electronic systems where developed. Modern ignition systems use a transistor switch instead of the points to interrupt the primary current.
Electronic controlled spark ignition
The transistor switch is steered by the ECU. The ecu contains a table for each engine speed and the belonging ignition triggering advance. Modern coil designs produce voltage pulses up 40,000 volts from the interruption of the 12 volt power supplied by the battery.
Close-up high voltage circuit
Engine lubrication
In addition to the obvious purposes of reducing friction and wear, the engine lubricant is called upon to aid in sealing; aid in cooling; protect components against corrosion; clean surfaces of deposits; and carry particles in suspension to the oil filter. The lubricant base stock, making up between 75 and 85 percent of the oil by volume, consists of a blend of hydrocarbons selected to provide the starting point for viscosity and lubrication performance.
An oil pump is used to draw oil from a sump or oil basin and supply it through pressurized passages to the majority of component interfaces susceptible to wear. Looking first at the automobile engine, the oil pump draws oil from the sump thought a pickup tube and sends it thought a filter to the oil rifle –a pressurized drilling running the length of the block. While the sump in most engines is contained in the oil pan beneath the crankshaft, dry-sump systems are sometimes seen. The dry-sump system is most common in very high performance engines, but is sometimes chosen for packaging reasons. With the dry-sump system, a second oil pump is used to immediately evacuate the returning oil from the oil pan, and send it to a separate reservoir from where it is again supplied to the engine. The resulting crankcase vacuum reduces pumping losses in the crankcase associated with piston movement. It also reduces the oil mist and further losses associated with fluid friction between the crankshaft assembly and the air and oil vapor in the crankcase. For our application, the losses should be minimal, thus one should opt for an dry-sump system. But as weight is also an issue, one should look for using one pump only, or even try to use none at all. If on places the separate oil tank below the engine, the fluid will flow automatically from the engine to the tank thanks to gravitational forces. When coming together in this tank, one can capture the oil, and using the pressurized air in the bottle available, it should be possible to inject oil clouds without any extra weight penalty causing system.
Therefore contact has been made with a firm specialized in lubrication systems for aircraft maintenance systems. They proposed to use their ‘dosage system for hand guided machines’. The system can inject oil ‘clouds’ triggered from pneumatic pulses. These pulses can be provided as mentioned by the pressurized bottle available. Placing a timing system in-between or a solenoid valve steered by the ECU can create an accurate lubricating system. The oil will flow automatically in the lower catch can, and when servicing the engine, it will be put again in the dosage system.