Direct Injection Fuel Pumps

[Joe L.]

As some of you may be aware, direct fuel injection is the "coming thing". It's being used to increase power, lower emissions and better fuel economy. Some of the GM Ecotec 4 cylinder engines and 6 cylinder DOHC engines already have it and the new Gen V small block will probably have it, too. With direct injection fuel is injected directly into the combustion chamber rather than into an intake runner. It achieves significant increases in power.

One of the problems with direct injection is that it requires very high fuel pressure, in the range of 200 psi or above. To achieve this the automakers will be going to cam driven, engine mounted, mechanical fuel pumps. Where have we seen this before? Back to the future?

[Clem Z.]

Re: Direct Injection Fuel Pumps

As some of you may be aware, direct fuel injection is the "coming thing". It's being used to increase power, lower emissions and better fuel economy. Some of the GM Ecotec 4 cylinder engines and 6 cylinder DOHC engines already have it and the new Gen V small block will probably have it, too. With direct injection fuel is injected directly into the combustion chamber rather than into an intake runner. It achieves significant increases in power.

One of the problems with direct injection is that it requires very high fuel pressure, in the range of 200 psi or above. To achieve this the automakers will be going to cam driven, engine mounted, mechanical fuel pumps. Where have we seen this before? Back to the future?

all the way to 2100# PSI and the diesel DI runs at 25,000 # PSI. that is a lot of pressure !!!

[Terry M.]

Re: Direct Injection Fuel Pumps

all the way to 2100# PSI and the diesel DI runs at 25,000 # PSI. that is a lot of pressure !!!

Not only is that a lot of pressure, but it is enough to be dangerous. Deisel mechanics are used to (or should be used to) the safety rules around that kind of pressure. Now the rest of us will have to learn a new set of rules and procedures.

[Clem Z.]

Re: Direct Injection Fuel Pumps

Not only is that a lot of pressure, but it is enough to be dangerous. Deisel mechanics are used to (or should be used to) the safety rules around that kind of pressure. Now the rest of us will have to learn a new set of rules and procedures.

thank god these new engine are much too complicated for the back yard mechanics to be working on as these systems hold lots of pressure even when the engine is not running and require a special bleed down method before you should try and work on them

[Bruce B.]

Re: Direct Injection Fuel Pumps

I'm curious as to what material is used in direct injection for the fuel lines and the actual transition into the cylinder?
I know on the current GM FI, plastic lines are used in most applications.

Also what type lines are used on the NASCAR injection units?

On the Hilborn I converted to electronic FI my fuel pump generates about 130 PSI but I reduce it to 49-51 PSI using a bypass regulator.

All my fuel lines are 6AN and tested to 170 PSI+

[Duke W.]

Re: Direct Injection Fuel Pumps

The injection pumps used by Daimler-Benz on the inverted V-12 aircraft engines and the post war 300SLR/SL were basically modified diesel injection pumps of the era. I don't know anything about the current designs, but am interested in obtaining a SAE paper or some other document that describes the details.

Fuel injected at the port begins to evaporate immediately and removes heat from both the incoming air and the port walls. This results in a slightly cooler charge at the end of the compression stroke, which theoretically allows a higher detonation-free compression ratio on a given octane fuel compared to a carburetor, but in practice the difference is small.

Injecting directly into the cylinder late in the compression stroke after the inlet valve closes means that all the heat to vaporize the fuel comes from the air and the combuation chamber surfaces. This results in a meaningful drop in temperature prior to ignition, which allows a meaningful increase in compression ratio for a given fuel octane compared to carburetion or port injection.

For those of you who attended my San Diego seminar or downloaded the pdf of the PowerPoint slides, you learned that thermal efficiency is a monotonic function of compression ratio, but it's not linear, and 14:1 represents a practical limit because at that point combustion chamber geometry becomes compromised with ever higher surface area to volume ratio, which increases heat loss.

Direct injection is more expensive than port injection, but upcoming fuel economy regulations are forcing the issue. The next generation small block should give us an idea of what direct injection can do. The displacement will be less, and I expect the bore centers will be reduced from the current 4.4", which will result in a physically smaller and lighter engine. Yet it will likely produce nearly the same torque and power as the current LS3 while using five to ten percent less fuel for all operating conditions.

Most current "low pressure" port injection systems have a fuel pump in the tank and a pressure regulator to maintain fuel pressure in the 40-60 psi range (depending on the design), which is injection pressure, so only the one fuel pump is necessary. Rubber hose in these systems is built to SAE30R9 requirements and is commonly called "fuel injection hose". Standard SAE30R7 fuel/evap/PCV hose should never be used for port injection applications.

The current NASCAR system is a typical low pressure port injection system, but I don't know if they have the pressure pump in the tank as in common on production cars or use a feed pump with the higher pressure pump downstream.

Direct injection will require a feed pump to the high pressure pump as was the case with most mechanical injection systems of the past.

Duke

[Bruce B.]

Re: Direct Injection Fuel Pumps

Duke,

The fuel lines on most current GM FI spiders are not rubber they a polymeric material ( ie: plastic) as shown in the attached picture which happens to be used on a GM V6.

The V8 assemblies are great for converting mechanical FI to electronic FI due to thier small size.

[Duke W.]

Re: Direct Injection Fuel Pumps

Thanks for bringing me up to date. Since my newest car is a 1991 model, I haven't kept up with all the technology changes including materials.

My Cosworth Vega, which was one of the first American cars with low pressure port or throttle body injection originally had the standard low pressure fuel hose, SAE30R7. This hose actually has a rated working pressure of 50 psi up to 3/8" (35 psi for larger diameters), so it was technically okay to use on the CV's 39 psi system, which has 3/8" hoses in the high pressure circuit downstream of the external Bosch injection pressure pump located on the underbody ahead of the right rear wheel. There is an conventional in-tank low pressure pump that supplies the Bosch pump. The Seville used the exact same Bosch injection pressure pump.

I think SAE30R9 spec hose showed up in the early/mid eighties as low pressure port/TBI systems became the norm, and I upgraded the CV to this hose in the early nineties. SAE30R9 hose has a rated working presssure of 180 psi, so it provides a lot more safety margin on a low pressure injection system.

Duke

[Dick W.]

Re: Direct Injection Fuel Pumps

The injection pumps used by Daimler-Benz on the inverted V-12 aircraft engines and the post war 300SLR/SL were basically modified diesel injection pumps of the era. I don't know anything about the current designs, but am interested in obtaining a SAE paper or some other document that describes the details.

Fuel injected at the port begins to evaporate immediately and removes heat from both the incoming air and the port walls. This results in a slightly cooler charge at the end of the compression stroke, which theoretically allows a higher detonation-free compression ratio on a given octane fuel compared to a carburetor, but in practice the difference is small.

Injecting directly into the cylinder late in the compression stroke after the inlet valve closes means that all the heat to vaporize the fuel comes from the air and the combuation chamber surfaces. This results in a meaningful drop in temperature prior to ignition, which allows a meaningful increase in compression ratio for a given fuel octane compared to carburetion or port injection.

For those of you who attended my San Diego seminar or downloaded the pdf of the PowerPoint slides, you learned that thermal efficiency is a monotonic function of compression ratio, but it's not linear, and 14:1 represents a practical limit because at that point combustion chamber geometry becomes compromised with ever higher surface area to volume ratio, which increases heat loss.

Direct injection is more expensive than port injection, but upcoming fuel economy regulations are forcing the issue. The next generation small block should give us an idea of what direct injection can do. The displacement will be less, and I expect the bore centers will be reduced from the current 4.4", which will result in a physically smaller and lighter engine. Yet it will likely produce nearly the same torque and power as the current LS3 while using five to ten percent less fuel for all operating conditions.

Most current "low pressure" port injection systems have a fuel pump in the tank and a pressure regulator to maintain fuel pressure in the 40-60 psi range (depending on the design), which is injection pressure, so only the one fuel pump is necessary. Rubber hose in these systems is built to SAE30R9 requirements and is commonly called "fuel injection hose". Standard SAE30R7 fuel/evap/PCV hose should never be used for port injection applications.

The current NASCAR system is a typical low pressure port injection system, but I don't know if they have the pressure pump in the tank as in common on production cars or use a feed pump with the higher pressure pump downstream.

Direct injection will require a feed pump to the high pressure pump as was the case with most mechanical injection systems of the past.

Duke

Most modern diesels use a fairly low pressure pump to supply fuel to the injectors. They also have a high pressure (3,000 psi) oil pump that operates the injector once the computer signals it to do so. The injection pressures vary from about 26,000 psi to 37,000 psi depending on the manufacturer and application.

[Chris H.]

Re: Direct Injection Fuel Pumps

Ford's Ecoboost motors use direct injection with fuel pressure at 2100 psig. I drove a Flex with an Ecoboost and it's a sweet motor. Smooth, quiet and fast. Twin turbo DOHC 3.5L V6 with 355 hp and a fat torque curve.

[Joe L.]

Re: Direct Injection Fuel Pumps

The injection pumps used by Daimler-Benz on the inverted V-12 aircraft engines and the post war 300SLR/SL were basically modified diesel injection pumps of the era. I don't know anything about the current designs, but am interested in obtaining a SAE paper or some other document that describes the details.

Fuel injected at the port begins to evaporate immediately and removes heat from both the incoming air and the port walls. This results in a slightly cooler charge at the end of the compression stroke, which theoretically allows a higher detonation-free compression ratio on a given octane fuel compared to a carburetor, but in practice the difference is small.

Injecting directly into the cylinder late in the compression stroke after the inlet valve closes means that all the heat to vaporize the fuel comes from the air and the combuation chamber surfaces. This results in a meaningful drop in temperature prior to ignition, which allows a meaningful increase in compression ratio for a given fuel octane compared to carburetion or port injection.

For those of you who attended my San Diego seminar or downloaded the pdf of the PowerPoint slides, you learned that thermal efficiency is a monotonic function of compression ratio, but it's not linear, and 14:1 represents a practical limit because at that point combustion chamber geometry becomes compromised with ever higher surface area to volume ratio, which increases heat loss.

Direct injection is more expensive than port injection, but upcoming fuel economy regulations are forcing the issue. The next generation small block should give us an idea of what direct injection can do. The displacement will be less, and I expect the bore centers will be reduced from the current 4.4", which will result in a physically smaller and lighter engine. Yet it will likely produce nearly the same torque and power as the current LS3 while using five to ten percent less fuel for all operating conditions.

Most current "low pressure" port injection systems have a fuel pump in the tank and a pressure regulator to maintain fuel pressure in the 40-60 psi range (depending on the design), which is injection pressure, so only the one fuel pump is necessary. Rubber hose in these systems is built to SAE30R9 requirements and is commonly called "fuel injection hose". Standard SAE30R7 fuel/evap/PCV hose should never be used for port injection applications.

The current NASCAR system is a typical low pressure port injection system, but I don't know if they have the pressure pump in the tank as in common on production cars or use a feed pump with the higher pressure pump downstream.

Direct injection will require a feed pump to the high pressure pump as was the case with most mechanical injection systems of the past.

Duke

Duke-----


GM's 3.6L DOHC V-6's with direct injection have a compression ratio of up to 11.5:1 and operate on 87 octane fuel.

[Duke W.]

Re: Direct Injection Fuel Pumps

Most modern engines , even "high compression", will operate detonation free on 87 PON fuel. For the Corvette LS3 91 PON is "recommended", but it is not required. GM does recommend 91 PON, minimum for the LS7.

Detonation sensors, spark retard, and mulitple spark advance maps will allow most "premium fuel" modern engines to operate on unleaded regular.

Spark retard might reduce low speed pickup and, maybe fuel economy, but the average driver will never notice any difference in either if they use regular unleaded in their "premium fuel" engine.

One exception may be modern boosted engines, especially turbocharged engines. They are set up to achieve high boost at low revs and less than premium fuel may noticeably reduce low end torque due to spark retard required to quell detonation at low revs and high boost.

Duke

[Clem Z.]

Re: Direct Injection Fuel Pumps

Most modern engines , even "high compression", will operate detonation free on 87 PON fuel. For the Corvette LS3 91 PON is "recommended", but it is not required. GM does recommend 91 PON, minimum for the LS7.

Detonation sensors, spark retard, and mulitple spark advance maps will allow most "premium fuel" modern engines to operate on unleaded regular.

Spark retard might reduce low speed pickup and, maybe fuel economy, but the average driver will never notice any difference in either if they use regular unleaded in their "premium fuel" engine.

One exception may be modern boosted engines, especially turbocharged engines. They are set up to achieve high boost at low revs and less than premium fuel may noticeably reduce low end torque due to spark retard required to quell detonation at low revs and high boost.

Duke

it does hurt the fuel mileage. i made a trip to bowling green with a fellow corvette owner and he had a 6 speed manual and i had a 4 speed auto with the 3.15 rear gear. i noticed when we filled up he took more fuel than i did as he was using regular and i was using premium