Please explain this difference between diesel and gasoline engines

[walnutman]

The ribbon heater isn’t for starting just for emissions reduction while cold. Crank time is longer on HPCR because the injection pump needs some speed to develop the pressure.

At the time you turn the ignition key to the ON position the PCM/ECM looks at the IAT temperature and determines if the manifold is cold enough to need pre-heating. Typically this occurs when temperatures are below 55-65*F. You'll notice that the battery voltage will fall slightly more than normal during this time that the WAIT TO START light is lit. Once started the grid heater will continue to cycle on and off to maintain proper manifold temperature. There are 2 grid heater elements. The PCM/ECM will determine if one or both elements will be used.
Here are the times and temperatures you should see.

Intake Manifold Temperature Key ON position
Pre-Heat Cycle Time
Ignition ON, Engine NOT Running
Post-Heat Cycle
Ignition ON Engine Running
Above 59F (15C)
0 Seconds
No
15F to 59F (-10C to 15C)
10 Seconds
Yes
0F to 15F (-18C to -10C)
15 Seconds
Yes
Below 0F (-18C)
30 Seconds
Yes
When temperatures are below 0*F it’s suggested to cycle the grid heater twice to help aid in starting. Block Heater use can offset intake temperatures, since the block will warm incoming air.

Grid Heater(s) - Power Requirement



1 Element
2 Elements
95 Amps
190 Amps
1140 Watts
2280 Watts
Starter – Power Requirement
350-700 Amps
(Depends on temperature and oil viscosity)
Alternator Output
120 Amps

As in anytime you start the vehicle and grid heaters are active it will take longer to recharge the batteries. So be sure to run the engine longer to ensure the batteries are charged back up. Typically about 10-15 miles is a enough distance to re-charge the batteries in arctic cold temperatures.

Both grids on will provide a heating temperature of 500F as proved in the video.


When the grids are running, you can tell when both or just one grid is running. You hook a voltmeter up to any point on the truck and measure exact voltage. In the video, you can see voltage drops to 11.75V, indicating that both grids are running. When the voltage slightly releases to 12.20V, one of the grids has stepped out. That grid then also steps out and regular charging voltage of over 13V is seen. Only one grid heater is needed after the initial dual grip operation to keep intake temperature up, so then you can see only one grid turning on and off with every time it drops to 12.4V.

Driving at low speeds can make the grid heater stay on seemingly endlessly as the cold air is driven into the engine at a high rate with the grids failing to heat it up to the temperature that the grids turn back off. You have to get the RPM and engine load just right, it also has to be during the state that you haven’t turned the grid cycling phase off (going over 20mph). Basically, you might be going 15mph up a hill and the grid will cycle on and instead of turning off the next second like normal, the threshold temp is never met and the grid will stay on for a seemingly endless time. Like I said, the conditions have to be perfect in order for it to do it. Just an interesting tidbit.. It is surely hard on the alternator and batteries.


The grid heaters will then shut down when you go over about 20mph, retain sufficient intake temperatures, or shut the engine back off. The grids typically run about 3 minutes while idling, cycling on and off to maintain temperature, and finally canceling the cycles.

Grid Relays



There are 2 grid relays, one for each grid heater. Each are ran by the ECM individually. The green wire on each of them is ground. The yellow and red wires are for each unique relay and serve as the positive lead that goes to the ECM. Upon being sent positive voltage, the relay energizes and the grid heater turns on.

 

[aircommuter]

All is still for reducing emissions. I have some Cummins units with grid heaters removed and dual air intake. They start instantly. The engine is used in other applications like crawlers and loaders before the were used in trucks and emissions weren’t of concern. They don’t have the heaters or an ECM. The 5.9 Cummins was a consolidated design with Case and Cummins.

 

[Shenandoah MF1760]

I know someone here can help me with this question. Maybe the question should be spark ignition versus compression ignition, but I will just use gasoline spark ignition vs diesel compression ignition. Anyway, gasoline engines are very sensitive to air/fuel ratios. For example, gasoline engines when run too lean can run way too hot and this can result in pre-ignition, burnt valves, and melted pistons. I have personal experience with a melted piston crown, darn it. So the air/fuel mixture is closely controlled. Diesel engines don't control the air at all, the engines are always sucking in as much air as possible. This means that the air/fuel mixture is all over the place. So why is it that a compression ignition diesel engine can tolerate the very lean condition at low throttle settings? And, from what I have read here, diesel engines run hotter at higher throttle settings and running them at too low of a throttle setting, such as excessive idling, can cause problems such as "wet stacking". The reason being that the engine is running too cool and all the fuel is not burning completely. It's just idle curiosity on my part and I figure a good answer is likely to be found here.
Thanks,
Eric

To answer the title question, diesel engines have a much higher thermal efficiency, around 20% better than the spark ignition system used by gas engines. This translates into more power and torque. This efficiency increases with load which is typically at a higher speed.

Air intake is not the same as gas engines which introduce a mixture of fuel and air during the intake stroke.

In a diesel, air is only drawn in during the intake stroke, and the fuel is admitted during the compression stroke when the act of compression has caused the air to be super-heated which ignites the fuel.

This super-heated air is why diesels don't have spark plugs and are the reason some direct-injected diesel engines don’t even require glow plugs to start.

The correct fuel-air ratio will be maintained by the engine itself, as long as there is plenty of air available. Too little air (or too much fuel) means black smoke.

 

[walnutman]

All is still for reducing emissions. I have some Cummins units with grid heaters removed and dual air intake. They start instantly. The engine is used in other applications like crawlers and loaders before the were used in trucks and emissions weren’t of concern. They don’t have the heaters or an ECM. The 5.9 Cummins was a consolidated design with Case and Cummins.

They don't always start instantly in sub zero temps. Ones without ECM's are not HPCR. But yes I agree the primary reason for the grid heater is emissions. A lot of performance guys remove the grid for better air flow.
The blanket statement "All is still for reducing emissions" is simply incorrect.
Read through the responses in this forum.

Grid Heater(s) Purpose ?

www.cumminsforum.com

 

[John0829]

Now, the injection system for fuel times the combustion event for optimum power based on RPMs, throttle input, or computer depending on the fuel system.

I agree to a point with what you said but also beg to differ, for example, take the OLD 2 stroke Detroit Diesel, it uses the camshaft to operate the injector, timing didn't change only thing that changed was the amount of air (obviously) and amount of fuel injected which was controlled by the rack and governor.

You ain't lived until you have climbed on top of a screaming run away 12V71 to shut it down because one injector failed in the WOT position (only position I ever saw them fail) and some idiot didn't bother to reconnect the emergency shutdown.

 

[aircommuter]

They don't always start instantly in sub zero temps. Ones without ECM's are not HPCR. But yes I agree the primary reason for the grid heater is emissions. A lot of performance guys remove the grid for better air flow.
The blanket statement "All is still for reducing emissions" is simply incorrect.
Read through the responses in this forum.

Grid Heater(s) Purpose ?

www.cumminsforum.com

I can tell you a lot more about these engines than you will read in these forums, i started in the engine rebuild business in 1972. I have owned numerous engines as well. You will encounter a lot things in life when you are told or recommended one thing but there is actually another underlying reason. It’s called duping.
Also the grid heaters were used in non HPCR versons that still cycle on and off after starting without a computer. But still for the same reason. They just didn’t have as many parameters.

 

[walnutman]

I can tell you a lot more about these engines than you will read in these forums, i started in the engine rebuild business in 1972. I have owned numerous engines as well. You will encounter a lot things in life when you are told or recommended one thing but there is actually another underlying reason. It’s called duping.
Also the grid heaters were used in non HPCR versons that still cycle on and off after starting without a computer. But still for the same reason. They just didn’t have as many parameters.

You ain't as smart as you tell yourself. That is a fact. The comments on that thread aren't what we are being told. It's actual experiences from people other than you.

 

[CalG]

I agree to a point with what you said but also beg to differ, for example, take the OLD 2 stroke Detroit Diesel, it uses the camshaft to operate the injector, timing didn't change only thing that changed was the amount of air (obviously) and amount of fuel injected which was controlled by the rack and governor.

You ain't lived until you have climbed on top of a screaming run away 12V71 to shut it down because one injector failed in the WOT position (only position I ever saw them fail) and some idiot didn't bother to reconnect the emergency shutdown.

IT takes more than a shop rag ! They go through the blower just as fast as you can get them near.
A good sturdy work coat stuffed in the inlet will do the job though ;-)

Don't ask me how I know this ;-)

 

[charlessenf]

a lengthily post. for simplicity, can you reduce your question to a sentence or two? regards

"So why is it that a compression ignition diesel engine can tolerate the very lean condition at low throttle settings?"
Was what I read.

 

[DieselBound]

It's all about the fuel! More energy content in diesel- energy density; takes a different approach to utilize. Diesel being oil-based is less corrosive- easier on metals. Higher compressive forces, however, means that crank, pistons rods etc HAVE to be more robust than their gasoline counterparts: this level gets bumped up when adding turbo-charging. Heavier stuff will require more energy to move around in which case the advantage is reduced (it'll take a lot of long math to figure out by how much).

I've gotten 820 miles on a tank of diesel in one of my cars (roughly 15 gallon tank). NOT going to be able to do that with gasoline (alone- hybrid is even iffy).

I am not comfortable storing volumes of gasoline. Advantage diesel.

 

[Thereisagod]

It's a combo of things. Diesel burns slower than petrol so the peak temperature isn't as high. Diesels are built heavier out of more sturdy materials. They run *very* lean compared to petrol. Diesels run slower so there is comparatively more time for the heat to disperse between ignition events.

You can still melt diesel pistons. Diesels come the other way where more fuel makes the combustion hotter. So winding up the fuel screw and hoping for the best is the same as leaning out the fuel on a petrol. Eventually you will get the piston hot enough to melt.

From a quick google, diesels run about 18 or 20 to 1 under high load, as opposed to petrol running 12.5 - 14.7 depending on your tune. Some petrol engines can run in lean burn for economy under light load but I don't know the specifics.

12.5:1 to 14.7:1 compression ratio in a petrol motor? I believe you're talking high performance sports cars and certain sports motorcycles. Most petrol engines are around the 10:1:1 to 12.5:1 ratio, even lower - unless I'm way out of date

 

[charlessenf]

It's actual experiences from people other than you.

Yes, that is called anecdotal information. Collect enough, verify details, add missing details, organize it logically and you've a potentially valuable database.

One thing about us humans is that we are generally unaware of what we are unaware of, tend to operate within the parameters of our individual experiential parameters (comfort zone).

Years ago when they first came out with the little tubes and egr valves and such to reduce emissions from my sixty-something Buick, I had a mechanic 'fix' an issue by cutting one of those 'extra' tubes and plugging the ends with a couple of bolts.

Now, some engineer working for GM with a fancy ass laboratory and all manner of air quality testing apparatus had designed thatl arge Buick engine and al the parts on it to function properly - including that black rubber tube.

That 'mechanic' has a story to swear by about how he 'fixed that Buick' he'll swear by. And, I have another.

 

[Rancher Ed]

The reason a gasoline engine will run hot and potentially melt pistons when run "lean" is that a diesel engine generally operators under a different portion of the "lean" spectrum. As shown below, peak flame temperature is achieved at the ideal air/fuel ratio (stoichiometric ratio), with the flame temperature being lower at both richer and leaner conditions.

In a gasoline engine, the goal mixture for maximum power is actually slightly rich. Visually this means the engine is operating somewhere on the sloped line between 0.5 and 1.0 in the above image. Adding air to the original "goal" mixture moves the air/fuel ratio closer to 1.0, which increases the flame temperature. This new condition is leaner than the original "goal" but is not actually "lean" in the absolute sense. If you continued to add air past the stoichiometric ratio the flame temperature would come back down and the engine would run cooler again on the right side of the peak.

This article from Summit Racing shows some common ratios for cruise, idle, and Wide-Open-Throttle relative to the stoichiometric ratio: Summit Racing - Air/Fuel Mixtures


Diesel engines operate on the opposite side of the curve: At idle they are way past 2.0 on the right side of the peak flame temperature with a very high air/fuel ratio. As more fuel is added, the air/fuel ratio gets richer and richer, moving the ratio closer to 2.0 and eventually 1.0 where the peak flame temperature occurs.


To summarize, they respond to becoming more rich or more lean differently because they operate on different sides of the peak flame temperature. WHY gasoline engines run slightly rich instead of designing the engine to handle the peak flame temperature is another topic, and likely has to do with engineering/control of the process, cost, emissions, and/or all of the above.

 

[JRH02]

Just build a triple turbo 12v Cummins at 700+ hp and have the best of both worlds.

 

[pmsmechanic]

The ribbon heater isn’t for starting just for emissions reduction while cold. Crank time is longer on HPCR because the injection pump needs some speed to develop the pressure.

The further north you live the more the ribbon heater is used for cold weather starting. Believe me on this.

Crank time on HPCR is longer because the engine needs to crank over enough times for the computer to figure out where tdc is. Once it knows that then it can compute the injection timing.

 

[Bentrim]

Yeah I know another long winded post--- Just hope it is worth the read. I know some can add to or even correct this information, but use it for what it is worth to you. Enjoy

The difference is in the properties of the fuel. Both most be atomized to burn properly.
Gasoline is usually mixed with air before it enters the cylinder and is compressed as a mixture to be ignited by a ignition source. That said I understand now there are direct injection gasoline engine, and I have not studied them yet.

A gasoline engine always has the air throttled and therefore is controlled on how much air/fuel mixture is allowed to enter the intake manifold and the cylinder.
Early farm tractors running "tractor fuel" (kerosene or distillates) had compression ratios down around 5 to 1, as gasoline became cheaper and more available compression ratios rose to 7 or 8 to 1.usually I have not found one above 8 to 1. Many of these low compression tractor could be "updated" to burn gasoline by replacing the pistons and intake/exhaust manifold. And then under extreme load preignition could be a problem. Even at these low ratios some attempted to use water injection to control preignition. Back in the muscle car era the higher compression of 12 1/2 to 1 was about the highest that could be safely run with Sunoco 260 the highest octane available on the street.

Gasoline start Diesel engines.
Early development of the Diesel engines found current electric starters did not have enough oomph to start them. Caterpillar used a hand started gasoline engine to start the Diesel. John Deere used a two cylinder engine on their first Diesel model R, For the next model 80 and later 2 cylinder Diesels they used a gasoline V4 until electrics caught up in about 1958, even then a compression release was still needed. IH on the MD used a 4 cylinder Gasoline/Diesel engine. (One side gas, the other Diesel)Pulling a lever opened a chamber in the head that lowered compression and exposed spark plugs. The engine then could be started on gasoline, after it warmed up the lever was pushed front and the engine was running on Diesel.

Diesel
Most Diesel engines run on an unrestricted air supply, Yes I have seen some with a throttle plate in tha air intake manifold (BMC Diesel in a Nuffield tractor)
Early Diesels used a energy cell or often referred to as a precombustion chamber. This help in many ways as it was easier on parts, and had less "Diesel knock", made it easier to build current production gas engine with a few modification to Diesel. Most early designs used an injector on one side of the head and the precombustion chamber on the opposite side, so the injection "shot" the fuel over the piston and into the cell (Oliver and MM), while some injected fuel directly into the cell (IH). The disadvantage was they were usually harder starting and required a starting aid when cold. Even some needed glow plugs after just being shut off!! (IH 282 in 560 and 706)
Direct injection eliminated a lot of issues, was more efficient, easier to cold start, but rattled more. They were also built heavier. The injector shot the fuel into a combustion chamber made in the piston. Even then some were very quiet as for Diesel noise (MM 585 in G1355 and White 2-150)

Diesel Fuel Injection
Not familiar with early fuel injection or new electronic fuel injection
Most early farm tractors used a rotary or inline injection pump. The rotary (CAV, Roosa Master, some Bosch) used a cam the "pushed" rollers together to generate the pressure required to pop the injectors, some had a timing advance built in and some did not advance.
Inline pumps used a row of piston/cylinder assemblies the ran off a camshaft to generate the high pressure.
All were governor controlled and varied the amount of fuel injected.
Cummins using the PT systems used the engine camshaft to operate the injectors and the amount of injection was controlled by the pressure in the fuel manifold.
I know Detroit was similar and used the camshaft but am not familiar with the control.
Modern electronics can vary timing, amount of fuel and even have multiple injections. Great for all around performance until the computer dies. That explains why they a so quiet and can produce so much power while reducing pollution.

 

[Willie B]

Diesel fuel is about 1.5 times the energy potential in a given volume of fuel. Diesel explodes more steadily expanding to push the piston down, less of a bang that gasoline gives. More power is extracted from equal energy from a diesel. Because compression is greater, motor components must be stronger.

 

[Brendanspapa]

In a diesel engine, the fuel burns relatively slowly, as it's injected into the cylinder, rather than rapidly, as in a spark ignition (gasoline engine). Further, the combustion (burning) process progresses only as it encounters enough oxygen in the cylinder, which may be further away from the point of injection. Combustion occurs at a constant pressure in a diesel, vs at a constant volume, in a gasoline engine.

 

[CalG]

As so many have offered, the difference is the fuel!

It's like comparing TNT with a lump of coal.

Both release heat on combination with reactive chemistry elements. But under controlled conditions, at different rates. Rate of heat generation results in Temperature.

Powdered coal can be very explosive... so can wheat flour.

Producer gas is a viable fuel source in desperate conditions.

 

[topgun05]

Crank time on HPCR is longer because the engine needs to crank over enough times for the computer to figure out where tdc is. Once it knows that then it can compute the injection timing.

Maybe in the most simplistic design IF motor stopped in worst spot it would need 2 crank revolutions for ECU to "figure it out" but anything built in this century will "know" the position in 1/4 to 1/2 of revolution no matter where it stopped.