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Return of the 2-Stroke Engine


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Poll: Return of the 2-Stroke Engine (8 member(s) have cast votes)

Returning to a 2-Stroke Engine is

  1. Great Idea (6 votes [75.00%])

    Percentage of vote: 75.00%

  2. Lousy Idea (2 votes [25.00%])

    Percentage of vote: 25.00%

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#1

dwightlooi

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Posted 25 September 2011 - 01:27 AM

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.

Posted Image

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.


Posted Image

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 by dwightlooi, 25 September 2011 - 01:37 AM.

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#2

67impss

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Posted 25 September 2011 - 07:54 AM

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 :smilewide:
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#3

riviera74

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Posted 25 September 2011 - 08:45 AM

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
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#4

dwightlooi

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Posted 25 September 2011 - 09:00 AM

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 :smilewide:


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.

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#5

Drew Dowdell

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Posted 25 September 2011 - 11:18 AM

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.
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#6

Z-06

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Posted 25 September 2011 - 12:34 PM

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?
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#7

dwightlooi

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Posted 25 September 2011 - 12:53 PM

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 by dwightlooi, 25 September 2011 - 12:57 PM.

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#8

dwightlooi

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Posted 25 September 2011 - 01:05 PM

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!
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#9

Drew Dowdell

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Posted 25 September 2011 - 01:36 PM

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.
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#10

dwightlooi

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Posted 25 September 2011 - 02:38 PM

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.
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#11

CanadianBacon94

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Posted 25 September 2011 - 03:04 PM

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
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#12

regfootball

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Posted 26 September 2011 - 10:29 PM

sure, lets get one running.!
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#13

dwightlooi

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Posted 27 September 2011 - 02:13 PM

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
Posted Image


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.
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#14

riviera74

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Posted 07 October 2011 - 08:48 AM

One last question: when will the SPOHV engine be ready to put in a car sold at a local dealership?
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#15

lngama

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Posted 18 July 2013 - 10:24 AM

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


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#16

dfelt

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Posted 18 July 2013 - 11:21 AM

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


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#17

lngama

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Posted 18 July 2013 - 04:49 PM

http://www.nasa.gov/...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...


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#18

lngama

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Posted 18 July 2013 - 07:08 PM

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....


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#19

lngama

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Posted 19 July 2013 - 09:01 AM

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.

twostrokeexhaust.gif

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.


advanced2stroke.jpg

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"


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#20

dwightlooi

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Posted 19 July 2013 - 12:04 PM

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 by dwightlooi, 19 July 2013 - 12:09 PM.

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