Return of the 2-Stroke Engine

[dwightlooi]

Why Two Stroke?

Because a 2-stroke engine fires twice for every firing of a 4-stroke engine. This means that the 2-stroke engine has potentially up to twice the output of a 4-stroke engine of the same displacement. Because it does twice the work at the same rpm, it also makes does it with half the parasitic friction (all else being equal). Eg. when both types were available on the market, no 125cc 4-stroke motorcycle ever makes as much power and/or weigh as little as a 125cc 2-stroke bike.

The problem with 2-Stroke designs...

However, the 2-stroke engine has many traditional short comings, some of them utter show stoppers. To begin with 2-stroke engines usually burn a premix of lubricant oil and fuel. This is because they tend to use the crank case as a piston pump to push the intake charge into the combustion chamber when both the intake and exhaust ports are open. This means that instead of having lubrication oil in the crankcase, they must fill it with a fuel, air and oil mixture. This is a serious problem because with enough oil content in the mixture to lubricate the load bearing main bearings, journal bearings and wrist pins, the mixture will burn in a smoky manner and is guaranteed to fail modern emission standards. Despite this, lubrication is still poor compared to 4-stroke engines leading to 2-stroke motors wearing out twice to three times as quickly as 4-cycle engines. To make matters worse, because both the intake and exhaust ports must be open concurrently at some point, 2-stroke cycles must either exhale the exhaust gases incompletely or over aspirate the intake charge such at a portion of the fuel-air mixture escapes into the exhaust. The former leads to reduced power output from not having enough air to burn all the fuel in the mixture. The latter leads to wasted fuel going straight into the exhaust. Both further compromises hydrocarbon emissions and lead to reduced fuel efficiency. As if that is not enough, the use of tuned exhaust systems provide a back pressure pulse to help achieve a balance between the two aforementioned problems also leads to a very narrow rpm range where the engine is optimally powerful, efficient and clean running. Even when everything is perfect, at the ideal rpm and load range, because both ports are on the lower lower of the cylinder scavenging is never as complete as a 4-stroke engine due to dead spots on the upper part of the combustion chamber and some degree of inefficiency cannot be avoided. All it all, inferior fuel economy, lousy emissions, poor longevity and narrow power bands have condemned the traditional 2-stroke engine to garden blowers and RC models. In fact, in many countries 2-stroke engines are outright banned not just on cars, but motorcycles and Jet Skis alike.

Direct Injected SPOHV Engine Changes Everything

Here I am presenting a concept that changes everything while retaining the advantageous of a 2-stroke design. The engine uses an overhead valve and side exhaust ports. Fueling is by means of direct gasoline injection during the compression stroke. It uses a wet sump lubrication system for the main bearings, journal bearings, wrist pins and part of the cylinder walls. The crankcase is filled with oil like a 4-stroke engine and is not used to pump a fuel-air-oil charge into the combustion chamber. Instead aspiration is enabled by an external centrifugal supercharger. The engine operates on a hybrid 2-stroke / Miller Cycle in that the intake valve stays open during a good portion of upward travel of the piston after the exhaust ports have closed. This results in an air charge that is above atmospheric pressure when the intake valve closes making this a true force induction engine. It also creates an asymmetrical compression and power stroke with the latter being longer than the former for superior combustion efficiency very much like Atkinson and Miller Cycle 4-stroke engines.

SPOHV Advantageous:-

Emissions: Because the engine does not burn oil and there is no fuel introduced into the engine by the direct injectors until after the exhaust ports have closed there is no possibility of unburnt fuel escaping into the exhaust or significant amounts of oil being combusted. Because of this emissions are squeaky clean.

Longevity: Because all the elements in the bottom end is lubricated in the same manner as a 4-Stroke engine, durability of the SPOHV design should be comparable to contemporary 4-stroke engines.

Performance: With twice as many firings at any given rpm, the SPOHV engine is potentially twice as powerful as a 4-stroke engine of equal displacement. This is further enhanced by the fact that because the heads only have to house an intake valve and no exhaust valve, whereas the side ports on the cylinder walls are exhaust only, the total area of the intake and exhaust openings are insanely high compared to both traditional 2-stroke engines and DOHC 4-valve 4-stroke designs. This allows the engine to be lighter and smaller than a 4-stroke engine of equivalent output. Potentially half the size.

Refinement: While the 2-stroke cycle does nothing to change the harmonics of any particular cylinder arrangement it does double the number of firing pulses at any given rpm. In this sense, a 4-cylinder 2-stroke engine has pulse intervals equivalent to an 8-cylinder engine.

Fuel Economy: For any given amount of power made in an engine of a given displacement, the SPOHV engine turns over at half the rpm of a 4-stroke engine. It also has only 1 intake valve and 1 camshaft compared to 4 and 2 respectively for a DOHC 4-valve engine. This equates to significantly lower parasitic frictional losses. With extremely high intake & exhaust cross sections, the engine also has lower aspirational losses.

SPOHV Disadvantageous:-

Forced Induction is a Must: Because the crank case is not used to push the intake charge into the the cylinders, an external compressor is a requirement. This can be a roots blower, centrifugal compressor, Lysholm Screw, G-ladder or even a piston pump. But some kind of air mover is needed and it cannot be a turbocharger because at idle with no load, the turbos will make no boost. Because the engine does not draw air into the cylinders with a downward stroke of the pistons and the engine won't run at all unless it is fed by a positive displacement air pump

Reduced Maximum RPMs: Because the engine has longer, heavier pistons as well as bigger heavier valves, the rpm limit is consequently lower.

Dual Exhaust Outlets: For optimal egress of exhaust gases the exhaust ports are on both sides of the engine block. This complicates exhaust routing a little, in the same manner that a V type engine does.

Hypothetical 2.0 liter 4-cylinder SPOHV engine statistics:-

Type: Direct Injected 2-Stroke, 4-Cylinder Engine

Valvetrain: Single Overhead Cam, 1-valve per cylinder

Construction: Aluminum Block & Heads

Aspiration: Centrifugal Blower Assisted, 2-stroke Miller Cycle

Bore x Stroke: 89 x 80.3 mm

Displacement: 1998 cc

Fuel Type: 87 Octane Unleaded Gasoline

Lubrication: Mobil 1 0W-20 Synthetic motor oil; 5 Quarts / 10,000 mile change interval

Power Output: 300 bhp @ 5200 rpm

Torque Output: 330 lb-ft @ 4200 rpm

Maximum Engine Speed: 5500 rpm

Edited September 25, 2011 by dwightlooi

[67impss]

I knew that 2 cycles shouldn't be dead but had forgotten about them for quite awhile. I always was thinking about how Detroit Diesel two cycles worked in a wet sump and the oil still contaminated the intake. NOW this makes perfect sense, one thing could the charge pump be made quite small? and with a variable output so as to allow for turbo supercharging? This may complicate the intake plumbing but lower pumping parasitic frictional losses while adding to fuel economy. Also I could see a very small version 750-800cc to be used as a range extender in Voltic systems. While we're thinking this way a diesel would also work in this environment I'd like to see those torque estimates.

Good work and thanks for the effort my mind is willing but my education holds me back

[riviera74]

Given that Hyundai has completely switched to 4 cylinder engines (Genesis and Equus aside), this could be a major advantage in the MPG wars we are now in. Since it seems that a lot of customers want to save fuel (i.e. smaller engines and ideally less weight), this SPOHV makes a lot of sense. Only problem is is that the perception will probably be off again since few seem to think that an OHV is any good compared to a DOHC engine of any kind. Having said that, this would make the basis of excellent and highly fuel efficient truck engines since OHV is more acceptable there. IF GM actually puts this type of engine in all of its 4cyl cars, watch for high MPGs. That would mean higher sales overall, other things being equal.

Don't believe me: Read this

[dwightlooi]

I knew that 2 cycles shouldn't be dead but had forgotten about them for quite awhile. I always was thinking about how Detroit Diesel two cycles worked in a wet sump and the oil still contaminated the intake. NOW this makes perfect sense, one thing could the charge pump be made quite small? and with a variable output so as to allow for turbo supercharging? This may complicate the intake plumbing but lower pumping parasitic frictional losses while adding to fuel economy. Also I could see a very small version 750-800cc to be used as a range extender in Voltic systems. While we're thinking this way a diesel would also work in this environment I'd like to see those torque estimates.

Good work and thanks for the effort my mind is willing but my education holds me back

Well, there are and have been, overhead valve diesels. But traditionally, these have port fuel injection or carburetion so there was still the problem of fuel following the intake charge into the exhaust due to cross aspiration. Also, aspiration is not as complete and volumetric efficiency is not as high when you rely on two or four into valves in the cylinder heads. This is simply because of the fact that if you have to split the head area between intake and exhaust valves, they cannot be as large as if the head only as to accommodate intake valve(s). Also, when airflow is not from one end of the cylinder to the other some degree of dead spotting on the base of the cylinder is unavoidable. With the SPOHV design, the intake and exhaust areas are much greater, plus the airflow is from the very top of the cylinder to the very bottom eliminating any stagnant areas.

The charge pump will be about twice the size of a supercharger on a 4-stroke, 2.0 liter engine with a similar specific output. This is because it has to effect both the basic aspiration (net pressure at 1 atmosphere) and whatever boost you pile on after the exhaust ports close. So picture something the size of a Vortec or Paxton blower used on a V8 used on a 2.0 liter 4-cylinder and you get the approximate idea. It's still not that big though. And part of the reason I am biased towards the centrifugal blower is because it is the smallest and most efficient (when at or near its optimal operating speed).

You can use a mechanical blower or positive displacement pump for base aspiration and a turbo for making boost above and beyond that. The Fairbanks-Morse Opposed Piston Direct Injected 2-stroke Diesels does just that. They use the blowers for starting but turbos for running. But these are usually marine diesels or stationary power generator engines, so they tend to run at a constant speed and load, and do not have to contend with the traffic light! You cannot use a turbo exclusively because then the engine won't run to begin with. You don't need it to be variable output, all you need is for it to move roughly just enough air as the engine would ingest without over pressurizing the charge. However, if you want to do this the mechanical air pump MUST be a positive displacement device -- a Roots, Lyshom, G-ladder or Piston Pump. It should not be a centrifugal blower because the boost from a parallel turbocharger can "backflow" through a centrifugal impeller. That is not to say you cannot have a variable output compressor. It is not functionally necessary, but you can. There are several ways to do this. Use a multi-speed transmission between the crank and the blower, use a CVT pulley pair or -- like the WWII German fighter engines -- use a hydraulic coupling to drive the supercharger which you can partially bleed to reduce the drive rate. But all of these increase complexity and add parasitic losses.

[Drew Dowdell]

Question: Reduced RPM verses what exactly? Reduced RPM verses a traditional 2-stroke I could see as being a good thing rather than a detraction. Even Honda owners don't want their engine buzzing away at 8,000 rpm all the time.

[Z-06]

How much fuel economy would you expect from a car like the Cruze or an E-46 3er weighing approx. 3,200 - 3,300 lbs harnessing this engine?

[dwightlooi]

Question: Reduced RPM verses what exactly? Reduced RPM verses a traditional 2-stroke I could see as being a good thing rather than a detraction. Even Honda owners don't want their engine buzzing away at 8,000 rpm all the time.

Versus a 4-engine of a similar displacement. The reasons are two fold. Firstly, the piston skirts need to be long enough to cover the stroke length. This is necessary to segregate the exhaust port from the oil filled sump. 4-stroke engines don't need such a long piston. To a lesser degree, neither does a traditional side intake port 2-stroke engine because that port does not need to be segregated from the crankcase. In fact it is fed by the crankcase with its fuel-oil-air mixture. Secondly, a single large intake valve offers the best intake port area. But it is also heavier than two small ones individually. Higher piston and valve mass means that the engine will not rev as high before bearing wear or valve float becomes a problem. You are looking at a maximum rpm in the 5000s rather than the 6000s or 7000s.

Regardless, I think 5000~5500 rpm is NOT bad. It's a very decent limit. Better than most diesels and on the lowest end of long stroke 4-stroker gasoline engines. One has to remember that a 2-stroker at 5,500 rpm is firing just as many times as a 4-stroke at 11,000 rpm. Therein lies the secret to making almost twice the output of a 4-stroke engine of similar displacement and cylinder count. An analogy can be made with the 1.3 liter Wankel Rotary. A Wankel fires 3 times per full rotation of the rotor. This is why a 1.3 liter RX-8 can make 250hp -- it is a lot more than 1.3 liters in air moved per revolution compared to a 4-stroke piston engine! Unlike a Wankel though, the SPOHV engine does not have the finicky apex seals requiring oil injection to lubricate. Also, unlike the rotary it performs compression and combustion in exactly the same place whereas the the Wankel does in in separate parts of the torcoid. Always compressing the charge on a cold part of the engine reduces thermal efficiency of the engine very much like running an engine that never warms up.

Edited September 25, 2011 by dwightlooi

[dwightlooi]

How much fuel economy would you expect from a car like the Cruze or an E-46 3er weighing approx. 3,200 - 3,300 lbs harnessing this engine?

Higher than a 2.0 liter NA 4-atroke engine for sure. But lower than a 4.0 V6 or 2.0 turbo making the same amount of power. If you compare it to either V6 or I4T 4-stroke solutions making the same 300 hp, I'll guess its in the order of about 80~90% of the fuel burn. About 2/3rds coming from the reduced frictional and pumping losses, 1/3 coming from the fact that the 2.0 liter engine is lighter and smaller.

For a car like a cruze, a 2.0 liter 2-stroke SPOHV is probably an overkill... that's a 300+ hp powerplant. A 1.0 liter 150hp/165 lb-ft 2-stroke engine will probably be better. Possibly a 3-potter in the displacement class. In that case, probably around 32 (city) / 49 (Hwy) mpg. It's substantial, but this is NOT Cold Fusion!

[Drew Dowdell]

What would the power curve on one of these look like? I'm all in favor of lower RPM anyway, so even after your explanation, I see it as a good thing. A 2.0 S/C 2 stroke should make roughly a little less than double the power ( taking into account supercharger losses) at a given RPM than a 2.0T 4-stroke.

Knowing what today's 2.0t engines are capable of doing.... I am perfectly fine with a 5,000 rpm red-line.

Any reason these couldn't be done in V configurations? I imagine the cylinder angle would have to be different than what we're used to with V6 and V8s today.

[dwightlooi]

What would the power curve on one of these look like? I'm all in favor of lower RPM anyway, so even after your explanation, I see it as a good thing. A 2.0 S/C 2 stroke should make roughly a little less than double the power ( taking into account supercharger losses) at a given RPM than a 2.0T 4-stroke.

Knowing what today's 2.0t engines are capable of doing.... I am perfectly fine with a 5,000 rpm red-line.

Any reason these couldn't be done in V configurations? I imagine the cylinder angle would have to be different than what we're used to with V6 and V8s today.

The power curve will be more peaky than a modern 4-stroke engine with dual VVT. Remember a mid-90s DOHC or SOHC engine before VVT, variable runners and low pressure turbos? Something like that. Let's say you have a torque peak at 4200 rpm, 1000 rpm above and below that is roughly where the meat of your power band is. Not the the engine chokes below 3200 rpm, but it may be a little soft and you may feel it "get on cam" at about 3K. Mainly because the exhaust port timings are fixed and a mechanical amplifies a torque curve it does not linearized it. That's the price you pay for nearly doubling the power density and enjoying frictional drag similar to a 4-stroke engine running at half your rpms. You can mitigate it a somewhat if you implement a variable volume exhaust resonator. But that will add to the complexity and may present a problem in modern automotive context in that the variable resonator needs to be between the exhaust ports and the cat converter slow light off and hurting cold start emissions.

If you choose to make it into a Vee configuration the bank angles will be the same for balancing purposes. However, exhaust routing may be a challenge given that you have exhaust coming out both sides as well as the middle of the engine Vee. Your intake air goes into the top of the valve cover... like a big fat spark plug tunnel if you will.

[CanadianBacon94]

exhaust timing isn't fixed on all two strokes, new direct injection two stroke for snowmobiles have whats called power valves where a electric motor pulls on a cable to move a small plate up or down on the exhaust port see diagram

[regfootball]

sure, lets get one running.!

[dwightlooi]

exhaust timing isn't fixed on all two strokes, new direct injection two stroke for snowmobiles have whats called power valves where a electric motor pulls on a cable to move a small plate up or down on the exhaust port see diagram

No, it doesn't have to be fixed. But they are a lot more difficult to control than take timing. You need a single slider valve and its control mechanism per exhaust port. This is compounded when you have exhaust ports on both sides of the engine. With intake timing control, all you have is a single phaser on a single camshaft. In a single cylinder 2-stroke engine, I guess this is irrelevant. But when you have 4 cylinders, 8 ports, 8-sliders and 8 actuators it becomes a handful.

For the purpose of managing exhaust impulse, a variable exhaust plenum is easier to implement. What you have is basically a wedge shaped volume, a flap on the input end that swings up and down to vary the size of the effective "slice" of the pie. Changing the volume changes when, and at what magnitude, the feedback pulse arrives back at the exhaust ports. When it arrives, it temporally pushes a portion of the exhaust flow back through the port, negating part of the exhalation.

[riviera74]

One last question: when will the SPOHV engine be ready to put in a car sold at a local dealership?

[lngama]

Hello...

big topic...I have solutions to eliminate or minimize the cited disadvantages:

- forced induction

- low RPM

- dual ehxausts

I can eliminate also the big input valve.

Studying this matter since 1993 I´ve found such solutions

There´s a bit of information at www.motor2t.net

[G. David Felt]

I like this, wonder if the engine would be workable at higher compression for CNG?

[lngama]

http://www.nasa.gov/centers/glenn/about/fs01grc_prt.htm

Look..2 cycle engines can use any feasible compression rate...Including diesel aplicattions.

Did I answered your question?

compressed gas should pass into a regulator to lower the pression...

[lngama]

One last question: when will the SPOHV engine be ready to put in a car sold at a local dealership?

Hi...let´s remember that this is a PROPOSITION...In a world that HATES 2 cycle engines we could expect to have them powering our cars in a short amount of time....

[lngama]

Why Two Stroke?

Because a 2-stroke engine fires twice for every firing of a 4-stroke engine. This means that the 2-stroke engine has potentially up to twice the output of a 4-stroke engine of the same displacement. Because it does twice the work at the same rpm, it also makes does it with half the parasitic friction (all else being equal). Eg. when both types were available on the market, no 125cc 4-stroke motorcycle ever makes as much power and/or weigh as little as a 125cc 2-stroke bike.

The problem with 2-Stroke designs...

However, the 2-stroke engine has many traditional short comings, some of them utter show stoppers. To begin with 2-stroke engines usually burn a premix of lubricant oil and fuel. This is because they tend to use the crank case as a piston pump to push the intake charge into the combustion chamber when both the intake and exhaust ports are open. This means that instead of having lubrication oil in the crankcase, they must fill it with a fuel, air and oil mixture. This is a serious problem because with enough oil content in the mixture to lubricate the load bearing main bearings, journal bearings and wrist pins, the mixture will burn in a smoky manner and is guaranteed to fail modern emission standards. Despite this, lubrication is still poor compared to 4-stroke engines leading to 2-stroke motors wearing out twice to three times as quickly as 4-cycle engines. To make matters worse, because both the intake and exhaust ports must be open concurrently at some point, 2-stroke cycles must either exhale the exhaust gases incompletely or over aspirate the intake charge such at a portion of the fuel-air mixture escapes into the exhaust. The former leads to reduced power output from not having enough air to burn all the fuel in the mixture. The latter leads to wasted fuel going straight into the exhaust. Both further compromises hydrocarbon emissions and lead to reduced fuel efficiency. As if that is not enough, the use of tuned exhaust systems provide a back pressure pulse to help achieve a balance between the two aforementioned problems also leads to a very narrow rpm range where the engine is optimally powerful, efficient and clean running. Even when everything is perfect, at the ideal rpm and load range, because both ports are on the lower lower of the cylinder scavenging is never as complete as a 4-stroke engine due to dead spots on the upper part of the combustion chamber and some degree of inefficiency cannot be avoided. All it all, inferior fuel economy, lousy emissions, poor longevity and narrow power bands have condemned the traditional 2-stroke engine to garden blowers and RC models. In fact, in many countries 2-stroke engines are outright banned not just on cars, but motorcycles and Jet Skis alike.

Direct Injected SPOHV Engine Changes Everything

Here I am presenting a concept that changes everything while retaining the advantageous of a 2-stroke design. The engine uses an overhead valve and side exhaust ports. Fueling is by means of direct gasoline injection during the compression stroke. It uses a wet sump lubrication system for the main bearings, journal bearings, wrist pins and part of the cylinder walls. The crankcase is filled with oil like a 4-stroke engine and is not used to pump a fuel-air-oil charge into the combustion chamber. Instead aspiration is enabled by an external centrifugal supercharger. The engine operates on a hybrid 2-stroke / Miller Cycle in that the intake valve stays open during a good portion of upward travel of the piston after the exhaust ports have closed. This results in an air charge that is above atmospheric pressure when the intake valve closes making this a true force induction engine. It also creates an asymmetrical compression and power stroke with the latter being longer than the former for superior combustion efficiency very much like Atkinson and Miller Cycle 4-stroke engines.

SPOHV Advantageous:-

Emissions: Because the engine does not burn oil and there is no fuel introduced into the engine by the direct injectors until after the exhaust ports have closed there is no possibility of unburnt fuel escaping into the exhaust or significant amounts of oil being combusted. Because of this emissions are squeaky clean.

Longevity: Because all the elements in the bottom end is lubricated in the same manner as a 4-Stroke engine, durability of the SPOHV design should be comparable to contemporary 4-stroke engines.

Performance: With twice as many firings at any given rpm, the SPOHV engine is potentially twice as powerful as a 4-stroke engine of equal displacement. This is further enhanced by the fact that because the heads only have to house an intake valve and no exhaust valve, whereas the side ports on the cylinder walls are exhaust only, the total area of the intake and exhaust openings are insanely high compared to both traditional 2-stroke engines and DOHC 4-valve 4-stroke designs. This allows the engine to be lighter and smaller than a 4-stroke engine of equivalent output. Potentially half the size.

Refinement: While the 2-stroke cycle does nothing to change the harmonics of any particular cylinder arrangement it does double the number of firing pulses at any given rpm. In this sense, a 4-cylinder 2-stroke engine has pulse intervals equivalent to an 8-cylinder engine.

Fuel Economy: For any given amount of power made in an engine of a given displacement, the SPOHV engine turns over at half the rpm of a 4-stroke engine. It also has only 1 intake valve and 1 camshaft compared to 4 and 2 respectively for a DOHC 4-valve engine. This equates to significantly lower parasitic frictional losses. With extremely high intake & exhaust cross sections, the engine also has lower aspirational losses.

SPOHV Disadvantageous:-

Forced Induction is a Must: Because the crank case is not used to push the intake charge into the the cylinders, an external compressor is a requirement. This can be a roots blower, centrifugal compressor, Lysholm Screw, G-ladder or even a piston pump. But some kind of air mover is needed and it cannot be a turbocharger because at idle with no load, the turbos will make no boost. Because the engine does not draw air into the cylinders with a downward stroke of the pistons and the engine won't run at all unless it is fed by a positive displacement air pump

Reduced Maximum RPMs: Because the engine has longer, heavier pistons as well as bigger heavier valves, the rpm limit is consequently lower.

Dual Exhaust Outlets: For optimal egress of exhaust gases the exhaust ports are on both sides of the engine block. This complicates exhaust routing a little, in the same manner that a V type engine does.

Hypothetical 2.0 liter 4-cylinder SPOHV engine statistics:-

Type: Direct Injected 2-Stroke, 4-Cylinder Engine

Valvetrain: Single Overhead Cam, 1-valve per cylinder

Construction: Aluminum Block & Heads

Aspiration: Centrifugal Blower Assisted, 2-stroke Miller Cycle

Bore x Stroke: 89 x 80.3 mm

Displacement: 1998 cc

Fuel Type: 87 Octane Unleaded Gasoline

Lubrication: Mobil 1 0W-20 Synthetic motor oil; 5 Quarts / 10,000 mile change interval

Power Output: 300 bhp @ 5200 rpm

Torque Output: 330 lb-ft @ 4200 rpm

Maximum Engine Speed: 5500 rpm

Why two stroke? Take a look at

This video show the real heart of an engine...To finish you´ll need only an enclosure to these pieces and minor pieces...

If the engine is a 4 stroke you will need another engine at the top dedicated to the valve system... So you can call the 4 stroke as a "valve engine"

[dwightlooi]

Why two stroke? Take a look at

This video show the real heart of an engine...To finish you´ll need only an enclosure to these pieces and minor pieces...

If the engine is a 4 stroke you will need another engine at the top dedicated to the valve system... So you can call the 4 stroke as a "valve engine"

A 2-stroke engine -- by definition -- is one which fires once every time the piston goes down and up -- hence 2 "strokes". A 4-stroke is one which fires once every time the piston goes down and up twice -- hence four strokes.

Most two stroke engines have ports, whereas four strokers have valves. But this is not strictly speaking true. You CAN -- as in the SPOHV design -- have a 2-stroke engine that has valves, or in the case of a more conventional design with overhead intake and exhaust valves which operate at twice the frequency as a 4-stroke engine.

Valves which we are used to are called poppet valves, but they don't have to be poppet valves. In fact, prior to and during WWII, a popular design choice is the use of "sleeve valves". Sleeve valve engines have ports on the side, no camshafts, no springs and look like 2-stroke engines. BUT, the intake and exhaust ports are covered and uncovered in succession by a rotating sleeve around each cylinder. The Bistrol Hercules(14-cylinder Radial) on the Beaufighter and Napier-Sabre (inline H-24 cylinder) in the Hawker Typhoon are widely used sleeve valve engines.

Edited July 19, 2013 by dwightlooi

[Z-06]

Dwight,

Let us start working on a working model of this.

[Drew Dowdell]

A 2.0T Ecotec can already do 300 hp with minimal effort... what advantage am I getting with a 2.0SPOHV 2 stroke?

[dwightlooi]

Theoretically about double the power density of a 4-stroke and twice the impulses per cylinder (a 3-cylinner will fire with the same frequency as a V6)

[dwightlooi]

Dwight,

Let us start working on a working model of this.

This may be easier than you think... especially if it's just a scaled mockup for show and tell.

Go model it in Solid Works, Creo or Catia. Save the model as a .STL file. Give it to a 3D printing shop and have it printed on some 3D printer of your preference -- SLA, SLS, FDM or Polyjet. It'll cost a few hundred bucks. You can print the block and heads in clear plastic with the internals in a solid color. You can then assemble it, turn the crank and have everything move. It's a one weekend project really.

[Drew Dowdell]

Theoretically about double the power density of a 4-stroke and twice the impulses per cylinder (a 3-cylinner will fire with the same frequency as a V6)

Right... his theoretical engine was only putting out 300hp from a 2 liter 2-stroke engine... I was asking what advantage I was getting since it wasn't in the HP dept.

[dwightlooi]

When you make 300 hp without having to run high boost + low compression, and when you move the same amount of air needed to make that 300hp by turning over at half the speed, your fuel economy is better. 300hp is from a air pump that moves at at roughly the same rate as the engine ingests it -- ie. very little boost just enough to overcome the residual pressure of the exhaust gases. Basically you are getting 3.6 liter NA V6 class output from a 2.0L with high compression and near atmospheric aspiration. If you feed it with 22~23 psi of boost like the 272hp 2.0T (LTG) does, you are looking at about 500 hp.

[lngama]

This one below at the link is a two stroke engine:

http://www.stuntbase.com/forum/kb.php?mode=article&k=30

People need only to eliminate the polution but

WITHOUT ADDING COMPLEX EXTRA PARTS. In this case is better to use a 4 stroke counterpart...

How can we achieve this goal?

I have some ideas..there´s a bit of them at www.motor2t.net

[G. David Felt]

Very cool sites Ingama, thanks for sharing.

[lngama]

Thank you.

[Guest Maciej]

http://www.youtube.com/watch?v=6lTwsy1oOR0&feature=share

http://www.youtube.com/watch?v=1TdK0gZsRp8

[Drew Dowdell]

that 2-stroke/4-stroke switching idea sounds neat.... but from the sound of it, they need to work on the NHV side of things still

[Guest Charlie]

Theres a Problem with the design pictured that would cause failures if built, the Ignition source needs to be central as the pressure during ignition will cause blowby and piston scoring, You could use a crescent shaped port opening instead. 

 

 

Also the heat generated in 2 strokes is a problem as they are firing twice as often as 4 strokes, when heat is built up it causes pre-ignition, this would be aggravated by the use of forced induction but could be managed as your only doing half the RPMs of a 4 stroke and you have large exhaust ports to vent the hot gas faster than a 4stroke. 

 

Build it!

[dwightlooi]

Actually this is a modern rendition of an old idea. 2-stroke engines with overhead valves and sleeve ports have existed before and had worked very well -- albeit mostly in diesel applications.

 

Remember the M113 Armored Personel carrier and the AMX13 light tank? They are powered by the Detriot Diesel Allison 6V53 engine in blown or turbocharged form. This engine had overhead intake valves, side exhaust ports and operates on an externally pressurized 2-stroke cycle. It did not have an overhead cam however, relying instead on an in-block cam, pushrods and rockers to operate the overhead valves. It is one of the most reliable and long lived tank engines. The Japanese Type 90 Main Battle Tank is another example of a heavy vehicle powered by an overhead valve, side port 2-stroke engine. In this case it is the Mitsubishi 10ZG32WT 10-cylinder 1,500 hp 2-stroke engine and this engine does employ overhead cams.

 

BTW, the spark plug does not have to be central. In fact in most 2-valve designs it is not. A centrally located spark is a  favorable design choice for combating detonation and knocks. Basically, you can think of knocking as a race between the spark initiated flame front and the flame front generated by hot spots in in the cylinder (usually near the rim of the piston). A centrally located spark offers the shortest distance from the spark to the furthest point in the combustion chamber. An offset placement is less desirable, but it is no worse than... say... using a larger cylinder bore which has the same effect.

 

Edited February 10, 2015 by dwightlooi

[dwightlooi]

BTW, the 6V53 displaced 5.2liters 318 cu-in (6 x 53 cu-in/cylinder). It made 275hp. This may not sound like much, but it is actually quite impressive given that this was the 1960s before electronic anything and this is a diesel engine. For comparison, the M60's AVDS1790 engine displaces  29.3 liters (1790 cu-in)  and made 750 hp -- that is 5.6x the displacement for 2.7x the output. Why? Because it is a 4-stroke engine and it fires each of its cylinders half as often.

Edited February 10, 2015 by dwightlooi

[G. David Felt]

Very cool history.

[loki]

i miss dwight's topics like this.

[G. David Felt]

1 hour ago, loki said:

i miss dwight's topics like this.

Totally agree, I wish he would come back and continue cool discussions like this.

[dwightlooi]

A little update...

There has been considerable interest in 2-stroke diesels lately. Companies like Achates are design new 2-stroke engines -- in the case of the Achates an Opposed Piston Diesel design with no cylinder heads, no valves, no spark plugs. Their first production engine is a 3-cylinder design which displaces 2.7 liters. It produces 270 bhp and 480 lb-ft.

Now, to be fair, the engine has six piston, two crankshafts and is closer in size to a 5.4 liter H6 than a 2.7L I3. But it has three advantages. Firstly, there is no camshafts, no cylinder heads and 40% as many parts. Secondly, because there are two pistons for each cylinder, the expansion ratio of each cylinder is twice that of a conventional engine of the same bore and stroke length which allows for insane effective stroke lengths (hence energy extraction) without high piston speeds. Finally, the thermal efficiency of the engine is above 40% (between 40.2 to 43%) across it's entire rev range which is about 15% better than 4-stroke diesels of the same output. A Silverado light truck so powered will deliver 37 mpg on the highway -- not bad at all.

A more interesting application for opposed piston designs is as a micro generator. A 400cc one cylinder O-P engine will generate about 30~35 KWe (40~47 hp). The supercharger (a necessity for 2-stroke O-Ps) can be a tiny and simple centrifugal impeller since this generator only needs to operate at its optimal rpm or not at all. It'll be spun up to its self-operating speed by the generator it drives before any fuel is ever injected. That is perfect as a range extender for electric vehicles. This is enough to completely recharge a 30KWh battery pack in an hous or maintain high way cruise at 60~80 mph while recharging the battery in about two. Effectively this means you CAN drive from San Francisco to LA on a full charge and about 6 gallons of diesel fuel. Not bad at all. Or, if you don't ever want to plug in that electric car you can drive around as a diesel powered hyrbid vehicle with about ~50 mpg and a ~300 mile range on that 6 gallon tank. Again not bad. The performance of the vehicle is quite independent of the generator or the battery capacity. It is governed largely by the size of the drive motor. Unlike the ICE , a big electric motor is not significantly less efficient than a smaller one (low load efficiency is about 70~75% vs about 90~95% at optimal). The single cylinder engine, its generator and the diminutive diesel tank will fit under the trunk floor in the same space currently occupied by a pair of mufflers and their exhaust pipes. Unlike a gasoline tank, rear placement is not a collision hazard because diesel spills are NOT flammable.

 

 

[Drew Dowdell]

What about diesel warm-up time @dwightlooi, or do these generators run all the time instead of start-stop like the Volt?

[dwightlooi]

1 hour ago, Drew Dowdell said:

What about diesel warm-up time @dwightlooi, or do these generators run all the time instead of start-stop like the Volt?

The way I will do it is for the vehicle to be a mid-range plug in electric with say a 20kWe battery. The car has no eCVT planetary transmission, just a direct drive motor like a pure electric. A 20KWe battery is good for about a 60~80 mile range (assuming regenerative braking) and direct drive. Unlike a Volt, this is actually enough for anyone with up to a 1 hour commute each way and a habit of driving to lunch or going shopping after work. But it is not so big that it has electric range which is not used on a daily basis. This is important because the battery is the single most expensive component of the EV. Saving $8000 in battery costs allow you to add a $4000 generator and still sell the vehicle for $4000 less.

If the driver does nothing, the Diesel Generator will automatically come on automatically when the battery drops to 20% charge and will cut off when it gets to 40% charge. That means it'll run for about 15 minutes at a time if you are cruising on the freeway or about 8 minutes if you are parked or sitting in stop-n-go traffic (give or take). More intrepid drivers can set the Generator on and off thresholds anywhere he pleases between 10 and 90%. Any time the driver pleases, he can depress the GEN switch which will turn the Generator On. When manually triggered, the generator runs until it is turned off with another tripping of the GEN switch or until the battery reaches 90% Charge (saving 10% to absorb regenerative braking energy recovery).

If you plug it in every night, the car behaves like mid-range electric such as the Leaf or an i3. The generator simply means that the car will never leave you stranded. If you never plug it in, the car generator will come on in 8 to 15 minute intervals, but drives just like a pure electric. If you are low of charge but can't plug it in for a while or if you never plug it in but want a full battery for some spirited driving, you can trip the GEN switch to keep your battery topped off. At full throttle a 200hp motor will drain that 20KWh battery from 90% to 20% in about 5 minutes (almost like in a RC Car).

The difference between this and a Volt or a Prius is that the single cylinder generator is nowhere near the cost, weight and size of an 4-cylinder ICE coupled to the drive line. The car has very simple powerplant consisting of a battery, a motor and an inverter (power converter) like a pure electric except it does not depend on a huge battery for practicality. The 400cc Generator installs like a pair of mufflers and is simply a mobile charger. The cheapest version of the car can have no generator. It can also be added later on with as much effort as replacing mufflers and plugging in a cable harness.

Because of the deep duty cycle, I'll very much prefer if the vehicle uses a Lithium-Iron-Phosphate battery rather than a Lithium-Cobalt-Oxide battery. Two reasons... LiFePO4 is much longer lived in deep discharge applications and LiFePO4 is inherently safe from thermal runaways and gasification (aka blowing up).

Edited November 29, 2018 by dwightlooi

[dwightlooi]

The original illustration was removed for some reason. Here it is again.

[Drew Dowdell]

What is the NVH of something like this?

[dwightlooi]

12 minutes ago, Drew Dowdell said:

What is the NVH of something like this?

NVH should be no better or worse I guess...

Maximum engine speed will be worse though. It'll be worse because the pistons are heavier (longer skirt needed to cover the exhaust ports), and also because you no longer have a dedicated exhaust stroke (at high speeds there will be less time for the intake air to push the exhaust out). This is why through flow side port engines -- including the Opposed Piston designs like the Fairbanks-Morse 38D8 1/2, Junkers Jumo 205 and more recently the Archates stuff -- tend to be diesels which do not rev that high anyway. It should be manageable up to 5000~6000 rpm or so using a rising rate supercharger (like a centrifugal blower). This is never going to be an Honda F20C, that's for sure.

[Drew Dowdell]

5 minutes ago, dwightlooi said:

NVH should be no better or worse I guess...

Maximum engine speed will be worse though. It'll be worse because the pistons are heavier (longer skirt needed to cover the exhaust ports), and also because you no longer have a dedicated exhaust stroke (at high speeds there will be less time for the intake air to push the exhaust out). This is why through flow side port engines -- including the Opposed Piston designs like the Fairbanks-Morse 38D8 1/2, Junkers Jumo 205 and more recently the Archates stuff -- tend to be diesels which do not rev that high anyway. It should be manageable up to 5000~6000 rpm or so using a rising rate supercharger (like a centrifugal blower). This is never going to be an Honda F20C, that's for sure.

Well, doesn't need to be high revving... these would make good compact power units for generators in PHEVs.