Let's bring back Throttle Body Injection?

[dwightlooi]

The Problem

Direct injection, as many of you know, allows for charge cooling, more precise fuel metering and a higher degree of atomization. This consequently permits a higher compression ratio to be adopted which in turn affords greater fuel economy and higher performance. Sounds good right? Well, there's a catch. Direct Injection also presents a few problems...

• Noise from the injectors
• Carbon fouling of the intake valves, intake tracts and/or throttle assemblies.

The reason is simple. Every engine has some degree of blow by past the valves when they are closed and many deliberately circulate exhaust gases into the intake side -- via valve event overlap and/or EGR valve(s) for emissions control. These "dirty" gases carry carbon particles (soot really) which over time can stick to intake valves, runners and throttles. In port injected or, heck, carburetor equipped engines the intakes are "wet". Fuel is constantly misted over the intake tracts and valves. If the gasoline is of any decent quality, it will containt detergents which gently cleans the valves of carbon deposits. It won't be completely spotless, but in general there won't be a problem with significant build ups. Direct Injected engines have completely dry intakes, anything stuck on this side of the intake valve never gets cleaned off.

Mitigation strategies are available. They generally involve timing and angling the fuel injection event so no fuel vapor gets back up the intake. Also, close tolerances of the valve seats may be specificed ensure that blow by is minimized. The valves and intakes can be coated to reduce the amount of carbon that actually sticks. Finally, combustion chambers and mixtures may be optimized to mimizing sooting. However, completely eliminating carbon particles on the intake tracts is largely impossible with a "dry" intake. And, many respectable companies (Audi comes to mind, BMW & GM too to a lesser degree) has serious carbon fouling issues on their direct injected engines. Carbon build up can be so bad that by 40K miles you may see a loss of about 10% of "when new" output. To make matters worse, there is no easy fix. Injector cleaners and oil additives do nothing because they don't reach the trouble spots. The only cure is for a complete dis-assembly of heads and manual scrubbing or replacement of the valves and other components -- which is essentially an engine rebuild.

To be honest, every DI engine has this fundamental problem. The difference is in degree. In an Audi RS4 for instance you'll lose 20~30 hp in 10,000 miles and for the 2.0T engines, its pretty darn ugly and somewhat performance impacting by 50~60K miles. In GM and BMW engines it's about ~1 secs off your original 0-60 times by 50~60K miles; build up is visible, yet not horrendous although it makes one wonder how these engines will perform at 200K miles. Ford and Porsche on the other hand have been relatively clean -- just thin visible coating of grey but no discernible impact on dyno or real world numbers. Toyota of course is completely free of the issue because they went to the complexity and expense of using both port and direct injectors on every cylinder.

The Solution

• Direct Injection for power
• Throttle Body Injection for idle and low rpm / low load
• 2-stage cam switching system between a 80% Atkinson and a High Performance Otto cycles*

* Otto Cycle Compression Ratio of 11.3:1 will become 9.0:1 with the Atkinson cam grinds in action. This reduction in compression allows the slightly uneven fuel distribution from the TBI system to not be an issue with pinging. The Atkinson cams also makes the compression stroke 80% that of the expansion stroke improving energy recovery for better economy.

Using the good old TBI scheme allows one to "wet" the intakes using one injector instead of many. This is especially economical when you talk about six or eight cylinder powerplants as opposed to Inline-3s and 4s because of the number of injectors needed to do it the Toyota way. Also, the good old TBI cleans from the throttle body all the way down the intake and right through the valves. A port injection system only cleans the valves and the very end of the intake. The reduced compression from the Atkinson cam also reduces combustion noise.

Ideally, the TBI system will be active only at idle and when creeping around at low rpms (below 1500 rpm). A little cleaning every day goes a long way! This is also when injector noise is most audible. And, even when cruising on the freeway way at 1800 rpm in top gear, only the direct injectors are in action. If you ever prod the throttle the direct injectors and otto cams come online too. Basically, it is a system for intake cleaniness and enhanced refinement -- the TBI injector is capable of supplying no more than ~10% of the maximum fuel demand of the car at WOT near the redline.

Edited April 29, 2013 by dwightlooi

[David]

So in reviewing all you have stated here, while I have voted for the TBI, I do think this is misleading and really needs to be reorganized into the following options

TBI - Only

TBI & DI - Only

DI Only

None of the Above, bring back a 4 barrell holly Carburator!

[dwightlooi]

I can't go back and change the post... the window for modification has timed out. Basically, what I was suggesting is that DI has an inherent noise and fouling problem which cannot totally be eliminated in DI only cars. Using an auxiliary TBI system allows you to:-

• Reduce the injector noise from DI when it is most audible
• Provide for the cleaning of the intake and valves to eliminate the fouling problems
• Do the aforementioned using a system that is least complex and least costly

The addition of the stage cam switching system and part-time Atkinson cycle merely compliments the idea by affording a way to alter the "effective" compression ratio to accommodate for the inferior knock resistance of the engine while operating with TBI. Fuel efficiency really doesn't matter at idle or in the parking lot given the low power demand, air flow and fuel use in those situations. A concentric lifter can be used to achieve cam switching. This is applicable to both pushrod and OHC designs and is quite possibly the simplest way of doing it.

[David]

Dwightlooi, Do you think a DI engine using Natural Gas will have this carbon problem? CNG seems to burn so clean in comparison to Petrol that I am wondering if you could go DI with CNG and us insullation to quiet the injectors?

[dwightlooi]

Probably not. Natural Gas is overwhelmingly CH4 (aka Methane), there are some trace aromatics and impurities, but generally no long chain hydrocarbons. It is technically not capable of producing soot or carbon compounds that cakes. The same can be said of slightly longer chain hydrocarbons like propane. In fact, one of the reasons Methane is being proposed as an alternative -- in a refrigerated liquid state -- to RP-1 (refined kerosene) in Kerosene / LOX rocket engines is the coking proof nature of the fuel which permits a fuel rich staged combustion cycle as opposed to an oxidizer rich cycle.

The problem with CNG is the poor storage density and high pressure tanks needed. Your car will go half as far and the tanks will eat up half the trunk space. Go check out a Civic HX... Gasoline and diesel are attractive because they are storable, dense and readily available. Also, CNG is already a gas. Hence, there is no charge cooling through direct injection and there is very little benefits to using DI with it.

Edited April 30, 2013 by dwightlooi

[David]

Being a distributor of Fuelmaker CNG home fueling appliance I do understand the clean side of a vehicle. The Honda Civic GX is an impressive CNG auto. Biggest benefits for CNG is in your trucks and full size SUV's. My 94 suburban I built up the Engine to be hi output and it requires Premium. Reduced my fuel cost to 85 cents per gallon by converting over to 130 Octane CNG. Clean buring, plenty of performance and plenty of room to keep it bifuel with storage tanks on the drivers side between the wheels and the tank in back.

Europe has plenty of CNG auto's that do not take up trunk space as they replace the traditional fuel tank area with CNG tank. So you could have TBI on an engine, run CNG which has the same energy as petrol and produce 2/3rds less green house gas at a much lower cost.

This would then take care of the carbon build up and no need for DI.

[Camino LS6]

Interesting stuff, both on the injection and CNG fronts.

I really want to build a CNG car.

[David]

Interesting stuff, both on the injection and CNG fronts.

I really want to build a CNG car.

Great thing about CNG is for GM fuel injected motors, there are amazing injector kits that just plug in with full wire harness so you can keep them Bi-Fuel Petrol/CNG and have an easy time running with minimal setup.

Check out www.NWCNG.com for Fuelmaker home fueling appliances and www.premiercngservices.com for some awesome conversion kits.

[dwightlooi]

Well, converting the country to a new fuel is something that isn't easy to do. We can't even get America to "accept" diesel as a mainstream fuel for non-commercial vehicles. The problem with CNG is that for the same storage volume you can store less of it compared to gasoline or diesel -- because it is a gas and because long chain hydrocarbons release more energy when broken down in combustion. A rough rule of thumb is that for the same storage volume (tank size) CNG has about 1/4 the energy content as diesel or gasoline. This means that for the same fuel tank volume a CNG vehicle goes 1/4 the distance all else being equal. This is exacerbated by the fact that being a pressure vessel, CNG tanks usually need to be cylindrical or spherical whereas unpressurized liquid fuel tanks can be any contorted shape. This is why CNG vehicles typically have to sacrifice passenger or storage volume for fuel storage, and still do not go as far on a full tank. As a "clean" combustible fuel, liquid Propane is probably better than CNG. It is liquid at very moderate pressures and room temperatures, it has a higher specific energy density and it is similarly available. The storage density advantages is why camping stoves and portable grilles -- which need to take their fuel with them and store it -- run predominantly on propane, whereas home kitchen stoves and heaters predominantly run natural gas (which is carried through pipes and need not be stored locally).

[Drew Dowdell]

We can't even get America to "accept" diesel as a mainstream fuel for non-commercial vehicles.

Yet.

Looking at take rates for diesel vehicles where the option isn't a huge price jump and diesels are very well accepted.

[David]

Well, converting the country to a new fuel is something that isn't easy to do. We can't even get America to "accept" diesel as a mainstream fuel for non-commercial vehicles. The problem with CNG is that for the same storage volume you can store less of it compared to gasoline or diesel -- because it is a gas and because long chain hydrocarbons release more energy when broken down in combustion. A rough rule of thumb is that for the same storage volume (tank size) CNG has about 1/4 the energy content as diesel or gasoline. This means that for the same fuel tank volume a CNG vehicle goes 1/4 the distance all else being equal. This is exacerbated by the fact that being a pressure vessel, CNG tanks usually need to be cylindrical or spherical whereas unpressurized liquid fuel tanks can be any contorted shape. This is why CNG vehicles typically have to sacrifice passenger or storage volume for fuel storage, and still do not go as far on a full tank. As a "clean" combustible fuel, liquid Propane is probably better than CNG. It is liquid at very moderate pressures and room temperatures, it has a higher specific energy density and it is similarly available. The storage density advantages is why camping stoves and portable grilles -- which need to take their fuel with them and store it -- run predominantly on propane, whereas home kitchen stoves and heaters predominantly run natural gas (which is carried through pipes and need not be stored locally).

I have to disagree with you on the 1/4 less than petrol. CNG is equal in energy content to petrol when you compare a gallon of Petrol to a gallon of CNG. Propane is clearly less pressure but has 1/3rd less energy in the same gallon. As such, all propane powered auto's loose HP, Torque and distance unlike CNG that is equal to Petrol on getting the same energy out of a Gallon of fuel. CNG being 130 Octane is much cleaner and actual increases HP and Torque figures.

[Drew Dowdell]

The real benefits of CNG (and indeed, even Ethanol) would be realized if there were engines built specifically for the fuel rather than modifying gasoline engines. What good is 130 Octane in an engine running 8.5:1 compression ratio when plain old 87 Octane will do just fine? Running super high compression ratios with these fuels would allow for much more complete use of the fuel even though there is less energy per unit of fuel. Instead of trying to run E85 through low compression 3.4 liter Impalas, they should have been running E85 as the preferred fuel through super high compression (12+:1 compression) 2.5 liter Impalas. It would have allowed for the same horsepower as the 3.4 liter but removed the perceived MPG penalty we associate with Ethanol today.

This was the giant misstep of Ethanol... not taking advantage of it's inherent gifts. Any future alternative fuel that aims to run through standard engines built for gasoline is doomed to the same fate.... including CNG.

[dwightlooi]

Well, converting the country to a new fuel is something that isn't easy to do. We can't even get America to "accept" diesel as a mainstream fuel for non-commercial vehicles. The problem with CNG is that for the same storage volume you can store less of it compared to gasoline or diesel -- because it is a gas and because long chain hydrocarbons release more energy when broken down in combustion. A rough rule of thumb is that for the same storage volume (tank size) CNG has about 1/4 the energy content as diesel or gasoline. This means that for the same fuel tank volume a CNG vehicle goes 1/4 the distance all else being equal. This is exacerbated by the fact that being a pressure vessel, CNG tanks usually need to be cylindrical or spherical whereas unpressurized liquid fuel tanks can be any contorted shape. This is why CNG vehicles typically have to sacrifice passenger or storage volume for fuel storage, and still do not go as far on a full tank. As a "clean" combustible fuel, liquid Propane is probably better than CNG. It is liquid at very moderate pressures and room temperatures, it has a higher specific energy density and it is similarly available. The storage density advantages is why camping stoves and portable grilles -- which need to take their fuel with them and store it -- run predominantly on propane, whereas home kitchen stoves and heaters predominantly run natural gas (which is carried through pipes and need not be stored locally).

I have to disagree with you on the 1/4 less than petrol. CNG is equal in energy content to petrol when you compare a gallon of Petrol to a gallon of CNG. Propane is clearly less pressure but has 1/3rd less energy in the same gallon. As such, all propane powered auto's loose HP, Torque and distance unlike CNG that is equal to Petrol on getting the same energy out of a Gallon of fuel. CNG being 130 Octane is much cleaner and actual increases HP and Torque figures.

I am sorry, I don't think that's scientifically accurate...

Here are the Volumetric Energy Densities of the fuels we talked about. It is given in Megajoules / Liter (MJ/L) -- a standard measurement of energy density per unit storage volume:-

• Pump Gasoline = 33.2~34.3 MJ/L*
• #2 Diesel Fuel = 37.3 MJ/L
• Jet A (Kerosene) = 33.1 MJ/L
• Liquified Natural Gas (cryogenic) = 26.0 MJ/L
• Liquid Propane = 25.3 MJ/L
• Ethanol = 24.0 MJ/L
• Compressed Natural Gas (@ 3625 psi) = 9.0 MJ/L
• Uncompressed Natural Gas (@ 14.7 psi) = 0.0365 MJ/L

* General = Generally speaking, the higher the Ethanol content the lower the energy density; 10% Ethanol blends have the worst energy density amongst Gasoline formulas. Octane boosting additives and detergents also generally reduce energy densities although extremely insignificantly.

Based on the above, I'd say that 1/4 the energy content is a reasonably accurate description. Now, CNG is also a lot lighter per unit volume. In fact, in terms of Mass Specific Energy Density it is not bad at all -- 53.6 MJ/kg vs 46.3 MJ/kg for Gasoline -- but we were talking about how far the vehicle can can go with a particular fuel tank size not fuel weight! Also, while Natural Gas weighs very little the tanks are large because it is a gas and densities are very low compared to liquid fuels. Also, to hold thousands of PSI of pressure, the tanks are heavy compared to gasoline and diesel tanks.

[David]

I will agree with your facts you have stated, though with 4th generation carbon fiber tanks, it seems we are getting light tanks with compressed gas and getting the power out of the source. LNG, Liquid Natural Gas has potential also.

No matter what form of fuel, I think there are benefits to both DI and TBI that we can use. I also think that Drew has a valid point that we need to be looking at higher compression engines to go with alternative fuels.

Interesting to see the fuels listed as such as I have always seen it as Gallon equal which gives vastly different numbers.

[dwightlooi]

I will agree with your facts you have stated, though with 4th generation carbon fiber tanks, it seems we are getting light tanks with compressed gas and getting the power out of the source. LNG, Liquid Natural Gas has potential also.

No matter what form of fuel, I think there are benefits to both DI and TBI that we can use. I also think that Drew has a valid point that we need to be looking at higher compression engines to go with alternative fuels.

Interesting to see the fuels listed as such as I have always seen it as Gallon equal which gives vastly different numbers.

If you express the numbers in MJ / Gallon the numbers will be different, but the ratios won't. It'll be like 62 mph is 50% faster than 31 mph. If you express it as 100 km/h and 50 km/h respectively, that's still 50% faster.

As so far as light hydrocarbon (gaseous) fuels go, I still very much prefer Propane. It is liquid at ~120 psi (@ 75 deg F) whereas Natural Gas is never liquid at any "practical" pressure. At room temperature, propane is about 25 MJ/L compared to with about 9 MJ/L for natural gas with 4000 psi tanks. Unlike CNG, rupture of a 100~200 psi pressure vessel is generally not explosive and not dangerous. The low pressures also means that the tanks can be relatively cheap and significantly lighter given the same construction compared to CNG tanks. From a handling standpoint, high pressure rigs are not required for refueling and processing gaseous propane into liquid fuel requires only moderate refrigeration to the tune of -44 deg F which is easy to achieve with common refrigerator technology without needing fussy cryogenic equipment.

Propane is about 110 octane. Not super high, but still notably more than gasoline. Allowing a compression ratios in the 13~13.5:1 range in an engine that is normally suited to 10.5:1 with Gasoline. Not bad. More importantly, Propane is metered as a gas, meaning that unlike liquid fuels port or direct injection is really unnecessary for precise fuel metering. Instead, you simply mix the propane with the intake air somewhere between the throttle body and the intake. Fuel distribution in the pretty homogeneous gaseous mixture will be even. As far as combustion cleanliness, it is practically as clean as CNG. C3H8 combustion results in CO2 and/or CO as well as water the combustion products -- no soot, no carbon fouling, no gunk, no particulates. Generally, there won't be a need for a catalytic converter and there is no issue with hydrocarbon emissions. The engine will be naturally smog free. If you run it very lean and very hot you do get oxides of nitrogen, but that's really from heating air itself really and anything that relies on atmospheric air for the oxidizer will form NOx if operated lean enough and hot enough since air is 21% oxygen and about 78% nitrogen.