Pickup Trucks 101: How Engines Work

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By Matthew Barnes

Most pickup trucks sold today have internal combustion engines. Passenger vehicles are powered by two main types of engines: compression, aka diesel, and spark ignition, aka gasoline. Besides the type of fuel they burn, what are the differences between a gasoline engine and a diesel engine?

Spark Ignition

Gas engine

Both spark ignition and compression ignition engines can work on a two- or four-stroke cycle. The more common of the two for automobiles, and certainly pickups, is the four-stroke. If we follow the path of the air entering a four-stroke engine, the strokes (or stages) in order are:

  1. Intake: The piston moves from top dead center to bottom dead center with the intake valve(s) open. If fuel is injected into the throttle body or intake manifold, then it is pulled into the cylinder with the air. If fuel is directly injected, then it may be injected near the end of the intake stroke and into the beginning of the compression stroke.
  2. Compression: All valves close and the piston moves from bottom to top dead center. Near the end of the compression stroke the spark plug fires, igniting the air-fuel mixture.
  3. Power: The piston moves from top to bottom dead center with all valves closed. The air inside the cylinder expands from the combustion of the air-fuel mixture. This provides the driving force for the engine.
  4. Exhaust: The piston moves from bottom to top dead center with the exhaust valve(s) open, pushing the exhaust out.

In spark ignition engines, the fuel can be injected into the intake manifold, just before the air intake valve, or directly into the cylinders, but it is always injected before the spark plug fires. Combustion occurs from the spark plug igniting the air-fuel mixture when the piston is very close to top dead center in the cylinder. The piston head and the cylinder head are typically shaped specifically for air flow into and out of the cylinder, and for the most even combustion burn throughout the cylinder as possible.

Spark ignition engines use a throttle to limit the amount of air entering the engine. Limiting the air will also limit the amount of fuel that is injected into the combustion chamber and therefore reduce the power output. Modern engines have sensors in the exhaust and intake to see how much air is flowing into the engine, and how much fuel is needed for a complete burn in the combustion chamber. The engine computer also controls when the spark plug fires. As you might suspect, these variables change with altitude (different ambient air pressure), engine load, engine rpm and weather conditions.

PUTC_gas_engine

Gasoline engines usually have a compression ratio around 10 to 1, which is about half of what most diesel engines run. The lower compression ratio helps stop preignition, which is when the air-fuel mixture ignites from being compressed instead of from the spark plug. Preignition can lower efficiency and power output, and when things really go bad it can heavily damage an engine. That's why using the proper octane rating for your vehicle is so important for proper engine health and longevity.

Spark ignition engines generally reach their peak power output at higher rpms when compared to compression ignition engines. With horsepower being a function of torque and engine speed, gas engines are typically better able to achieve higher horsepower than diesel engines. They also rev faster due to a faster energy release and lighter (less heavy duty) rotating mass. The faster energy release comes from the spark ignition and using gasoline instead of diesel fuel. When compared to diesel fuel, gasoline is more refined as well, and is easier to ignite — it also burns cleaner and quicker. This is one reason why most high-performance vehicles use spark ignition engines.

Compression Ignition

Diesel engine

Compression ignition engines also most commonly run on the four-stroke cycle; however, compression ignition engines differ from spark ignition engines in many ways. For example, compression engines don't have a traditional throttle, the compression ratio is significantly higher, they use a different fuel, the fuel is injected at a different time and place, and the fuel is ignited using a completely different method.

For compression ignition engines, there is no throttle to restrict air flow while the engine is running. This means that no matter what the load might be on the engine, the same amount of air will enter the cylinders. This also causes the engine to spend a significant amount of its life running in a fuel lean state, making the engine run hotter, but compression engines are built to compensate for this.

Compression ignition engines ignite the air-fuel mixture by heat and compression rather than the spark plug igniter of a gasoline engine. For this to work effectively, the engine needs to have a high compression ratio; many diesel engines have a compression ratio in the 20-to-1 range. As you might imagine, this puts a lot more stress on the engine components, but also allows the engine to have a higher torque output.

PUTC_diesel_engine

Because compression ignition engines need heat for the ignition to happen, they are susceptible to hard starts in cold environments; however, technology in diesel engines has come a long way, and most modern diesel engines can be started even in extremely cold temperatures, without the use of an engine block heater.

Fuel is injected directly into the cylinders. To avoid preignition, fuel injection starts at the end of the compression stroke when the piston is very near top dead center and continues with most of the fuel being injected during the power stroke. The injectors must also inject the fuel at very high pressures to overcome the higher compression ratio. Spark ignition engine fuel injectors run in the 20-to-50 pounds-per-square-inch range, while modern compression ignition engine fuel injectors run in the 30,000-to-50,000 psi range. The high-pressure injection also helps to better atomize the fuel, making for a cleaner and more complete burn.

17ford_f-250-diesel

Ignition begins as soon as fuel is injected into the cylinder and continues until fuel stops being injected. In theory, spark ignition can be thought of as an instantaneous ignition where all the fuel is burned in a very short amount of time. With compression ignition the opposite is true, the fuel is burned more slowly over a longer period.

Diesel engines tend to have high torque output at a low rpm. This torque comes from the longer fuel burn time, diesel fuel having more energy by volume and the high compression ratio. To handle the extra force on the engine, many of the components of a diesel engine are larger or use higher-strength materials. This makes diesel engines ideal for heavy work loads, especially when they are run at a constant rpm. Power generators, ships, trains (modern trains use diesel generators to power electric motors) and heavy equipment all use diesel engines because of the high torque output at lower engine speed. Another benefit to a diesel engine is that the higher compression ratio aids in engine braking. For pickups, diesel engines are great for towing heavy loads over long distances and typically provide longer life cycles.

Final Thoughts

There are advantages and disadvantages to spark and compression ignition engines for pickups. Diesel engines are built with stronger components and move at slower speeds, which helps with their longevity. Diesel engines also weigh significantly more than similarly sized gas engines. Gas engines will cost less up front, but diesel engines hold their value over longer timeframes. However, with newer emissions restrictions, diesels no longer provide a significant fuel economy advantage over gas engines, especially when running lighter loads in full-size pickups.

Cars.com graphics by Paul Dolan; Cars.com photos by Matthew Barnes and Angela Conners

Comments

I still believe a 2 stroke engine would be better suited for trucks.

Diesel all the way, never look back.....

Not once in this article is the word 'turbocharger'
That is why diesels engines "tend to have high torque output at a low rpm"
The term pressure ratio should be used instead of compression ratio.
If a diesel has a numerical 15:1 compression ratio, and the combination of late [past BDC] intake valve closure + boost pressure means you will have a 30:1 pressure ratio; versus the gas engines 10:1 {late intake valve closure is offset by resonance charging}-that is how diesels feel powerful.

I hope the author goes on to discuss electric drivetrains using battery, fuel cell and engine energy sources. Whether y'all like it or not, those ARE coming to trucks eventually and I expect sooner than most of you want to believe.

Whether y'all like it or not, those ARE coming to trucks eventually
Posted by: Road Whale | Oct 12, 2017

@Roadwhale

As the price of regular unleaded continues in the $2 range, the interest in expensive and exotic alternatives dies. Not an opinion, just a fact.

I would love for a follow on article on Hybrid, and Battery operation.

Also the pros and cons of each would be nice.

Diesel mileage and reliability advantages have largely been neutralized by complicated exhaust systems. The cost to own and operate a diesel has become prohibitive for one who does not have the work/loads to constantly justify the added costs. For one who does not constantly work their truck very hard gas makes much more sense in costs. For one that does diesel is the preferred choice but the costs are high.

@clint, it depends on how you look at it and what you do with it. For example, my Ford diesel is used to tow my boat or my camper (5200lbs, 10K pounds), I have a car as a DD for work. My truck gets about 8500 miles put on it a year, mostly towing. My maintenance is done once a year (oil, filters, fuel filters). For what I tow the diesel is king, as I have owned both, sure the gassers may be cheaper on maintenance, but I have not had to worry about the costs for the damage done by towing things with gassers, so in my case diesel is better. However if it was also my daily driver, I may not feel the same way.

Mark and PUTC staff - - -

Great article for basics. Nice diagrams. Keep it up.

Yes, there are opportunities for future issues with regard to turbos and hybrids, but I love this for a good start.

Or maybe articles on advanced designs of ICE's, such as those listed here:
https://www.caranddriver.com/flipbook/12-propulsion-technologies-that-will-increase-future-cars-efficiency

====================

Diesel ALL the way, never look back.....

I have a car as a DD

These statements are not congruent.

I'd diesel was the way, when drive a car?

Oh wait.

However if it was also my daily driver, I may not feel the same way.

That's right. Diesel is not the way. The truth shall set you free.

I have not had to worry about the costs for the damage done by towing things with gassers, so in my case diesel is better. Posted by: Nitro | Oct 12, 2017

@Nitro

I drove trucks for a living when I was young. I bet 90% of miles logged was pulling trailer loads with a gas V8 one ton truck.

Years later a friend of mine still was driving that old thing and he never had engine trouble with it. It was an International Harvest dump. Bullet proof motor, trans and rear end.

Your suggestion that gassers have high maintenance costs when used in a heavy duty environment cracks me up.

Back in the 1950s & 60s all the school buses, beer trucks, grocery trucks and a lot of over the road trucks had big gas powered V6 engines. They had shorter rebuild cycles than they do today, but if you didn't abuse them they'd work hard for 50k miles, get a valve job or piston rings and go right back to work.

In those days you could overhaul a gas engine for less than $500 bucks unless you had trashed the block.

I am so glad Mark posted this article. Now I am an 'EXPERT' on the workings of an engine. After 74 years of living, I feel so better informed on this subject. (Sarcasm) My dad taught me this when I was 7 years old.

My dad taught me this when I was 7 years old. Posted by: TUNDRA forever | Oct 12, 2017

@Tundra

Older guys like us can remember a time when you might actually have to work on your motor or replace a part. The young guys today buy a new truck and never pull as much as a valve cover.

I still believe a 2 stroke engine would be better suited for trucks.
Posted by: papajim | Oct
/QUOTE

Runs too dirty,,,forgetaboutit..

"pickup-trucks-101-how-engines-work"

If one looks at posts typical of this site, no one looks beyond the badge on the grill.

Older guys like us can remember a time when you might actually have to work on your motor or replace a part.
The young guys today buy a new truck and never pull as much as a valve cover.
Posted by: papajim | Oct 12,
/QUOTE

Thank goodness,,I like to drive them not fix them..LLL

As the price of regular unleaded continues in the $2 range, the interest in expensive and exotic alternatives dies. Not an opinion, just a fact.
Posted by: papajim |
/QUOTE

You are wrong,
,,electric motor is 99% efficient and has way more torque right at the bottom,,has or diesel dont even come close

Watch Tesla vs Corvette

https://youtu.be/UgZJg6Mu0cU

Chevrolet builds a better way to see the USA | Oct 12, 2017

Please cite specifics! Go back over the last five price drops in unleaded gasoline and EVERY time it crushes investment in alternative systems. I'm not making it up.

Why not look it up and report back to the group?

Diesel ALL the way, never look back.....

I have a car as a DD

These statements are not congruent.

If diesel was the way, why drive a car?

Oh wait.

However if it was also my daily driver, I may not feel the same way.

That's right. Diesel is not the way. The truth shall set you free.


Posted by: papajam's hot secretary | Oct 12, 2017 11:18:46 AM

I agree with Papajim's secretary.

Nitro, Vased on your incongruent comments on diesel and overall lack of knowledge, and transparency in that you drive cars, we must inform you that your statements will be disregarded until further notice.

Nitro got owned. lol.

Unless your over 11k lbs daily towing a hd gas engine works fine. As a matter of fact the ram 3500 with 6.4 and 4.44 gears in a srw cab chassis regular cab has a tow capacity of 17,600+ lbs I think that's 4x4. You can get a Ford with a 4.30 in a f350 gas job that also will tow similar numbers I think. You want an f450 with a v10 and 4.88's that's another option, Thats over 17k over towing too. I would prefer the v10. I have one I drive daily now. The ram is available on a 3500 with a rsc66 option trans with better gears than a rfe. It should be better but I haven't had my hands on one yet.

@papa, based on your previous comments, I cant respond to you anymore.

How Engines Work, Well chances are if its a Ford engine it don't work! Because well their all junk!

@papa jim--I never overhauled and engine but I did my fair share of tuning them up, changing oil, replacing a carburetor, and changing points and condenser on the spot pre electronic ignition. My father had a 62 Chevy II 300 which I drove during high school and first few years of college. I did all the maintenance on it and kept the exterior and interior clean. I waxed that car 3 or 4 times a year. I drove my granddad's 68 IH tandem axle steak bed truck with a dump and his 63 IH step side truck when I spent the Summers on my grandparents farm. All my granddad's tractors were gasoline. I don't remember them being unreliable or requiring a lot of maintenance. Having said that vehicles in the 50s, 60s, and 70s required maintenance more often with shorter maintenance schedules but as long as you took care of them they were very reliable. As the tractors and trucks became bigger and the acreage to farm became larger farmers started using diesel because they were more efficient and the diesel fuel was less expensive. Most of us really don't need diesels and the additional cost of a diesel is not practical. I would only buy a diesel if I needed one for towing or for a business purpose. Nothing against diesels just that it would be a waste of money for me just as a full size pickup is a waste for what I use a truck for. An extended cab midsize pickup does everything I need it to do from getting rid of things I no longer need, hauling away yard waste, picking up a scoop of mulch, hauling my riding mower, and many other things.

Electric motors are not "exotic".

combustion engines are far more exotic.

Electric cars were the first cars made because they were far simpler. You can't get simpler than an electric motor. Heck, I've even built one when I was a kid from scratch.

Combustion engines have any moving exotic parts that must be timed just right and fit just right.

Once a power source for electric motors is worked out, which it will soon, electric motors will power 95 percent of ground based vehicles. And eventually, a lot of air vehicles too.

Has anyone thought about how much more crude oil or Coal, nstural gas will be needed, when all electric cars are plugged in at night. Power Plants will have to be increase to power all these millions of electric csrs. Please explain how these cars will not demand electricity from power plants when there all plugged in at night ?

how much more crude oil or Coal, nstural gas will be needed, when all electric cars are plugged in at night. Power Plants will have to be increase to power all these millions of electric csrs. Please explain how these cars will not demand electricity from power plants when there all plugged in at night? Posted by: Ray | Oct 14, 2017

@Ray

That's the easy part.

The cost of transitioning cars/trucks/buses that run on gas and diesel (including the infrastructure) to electric is the bitch.

The electric propulsion on a day-to-day basis is a huge advantage if you can subtract the costs of transition, and the amount of time it takes. It will happen but most of us will be dust by then, i.e., a very long time.

@Ray, there's more.

During the last 20 years Minnesota has spent around ten billion dollars on green energy infrastructure, such as wind farms and transmission lines.

Energy prices there, however, have risen from about 18 percent below the national average from 1990 to 2009 to above average for the first time during 2017.

Minnesota has lost their competitive advantage with little to show for it.

Minnesota law had ambitious carbon-reduction goals. Starting with a baseline of carbon production in 2005, the state was supposed to achieve a 15 percent reduction by 2015. They came up well short of that.

During the time that Minnesota was using its tax dollars to fund this experiment in wind technology, the price of fossil fuels crashed to 1960s levels (adjusted dollars).

I don't say this to knock their intentions or their effort, instead I mention it because it takes years for these investments in wind farms to pay off. Eventually it will, but not right away.

@Ray--Agree on natural gas and coal but power plants don't burn crude oil or any product produced from crude oil. We have plenty of natural gas due to fracking. The problem is not the lack of fuel more like an aging power grid and not enough power generating plants which can eventually be solved but it will take years. The main obstacle will be the lack of infrastructure to charge batteries and the cost, size, and range of the batteries. This too will most likely be solved but then it will take years. I wouldn't mind having an electric vehicle but because of the above I would not jump on the bandwagon just yet. I am usually a late adopter of things. In the meantime most internal combustion engines have become cleaner and more efficient and hybrids have become very affordable and reliable.

I don't drive as much as I use to and keep my vehicles for 10 + years so just buying a new vehicle to save some money on fuel is not enough but when it comes time to replace one of my vehicles because of wear and tear I do consider fuel efficiency along with safety, comfort, reliability, and what meets my wife's and my needs best. Cost of a new vehicle along with depreciation for the most part will more than offset the savings gained from fuel efficiency. I have become more pragmatic about vehicles and other things as I have gotten older and want to get my money's worth out of everything I buy.

You can tow 19,500 with a 6.4 Hemi v8 Ram.

Jeff S., all you need is a Prius and a $1000 Harbor Freight fold-up trailer. A truck does not perfectly match your needs and therefore I must post on this site and notify you immediately of your extravagant truck purchase. I will continue to post about needs being perfectly matched and help you decide that you do not need one ounce more truck than necessary!

I also want to bring up that bacon and lettuce sandwich you ate today. There was a little too much mayo. You enjoyed it a little too much. One less slice of bacon meets your needs as well. That would result in 25% less pig consumption rate, resulting in less farm land and farmers destroying the environment.

I have to admit that I was expecting lots of captain obvious I’m this article. Not so! Well done PUT.com!

I think diesel hybrids or diesel 2 mode hybrids are the best for pickup trucks. The diesel hybrids can get the torque all time and because the engine is on constant load and rpm ,it will burn clean with very high efficiency.

Two power systems increase complexity and cost to an unacceptable level. The engine compartment of my 6.7 powerstroke already resembles the complexity of a Saturn V rocket motor. Just because you can dream it up, doesn’t mean it is practical.

I think diesel hybrids or diesel 2 mode hybrids are the best for pickup trucks. The diesel hybrids can get the torque all time and because the engine is on constant load and rpm ,it will burn clean with very high efficiency. Posted by: Unni | Oct 16, 2017

@Unni

What about an alternative? Instead of the cost of building diesel engines, use a gas engine that exists solely to recharge a battery?

Gas engines are easily built with the flexibility to use various blends of gasoline, ethanol (or methanol) without much extra cost or hassle. Full time electric motor operation, plus Re-gen braking and you've got a powerful, clean burning and long lasting drivetrain without the complexity that Puddycat is talking about.

@papajim
Trains runs like that, ( series hybrid ) ex: from wiki :https://en.wikipedia.org/wiki/Diesel_locomotive#/media/File:DieselElectricLocomotiveSchematic.svg

The advantage is no complex transmission needed. The other good part is its more future proof ( ex:can change with fuel cells or batteries or so as technologies evolve ).

@Unni

The diesel needs to live in a place where the motor runs hard and runs almost all the time (18 wheeler?).

All engines don't run as well when they're cold, gasoline engines included, but diesel really suffers if it's not fully warmed up.

This is why I proposed a gas engine instead of a diesel for your hybrid drivetrain. The fact that gas engines are more fuel flexible and cost less to build is gravy. Gas engines in a direct hybrid model like we're discussing can run as stationary engines at a fixed (optimal) RPM to make the most of its fuel, and harmonize the engine's internal components.

As long as fossil fuels remain as plentiful as they are today it is hard to imagine a scenario where "the good" will be sacrificed for the "perfect."

@papajim

When we go to a level of series hybrid design, the engine /fuel looses it significance very much because, we treat it as a generator and we need to choose a right generator . Even the ICE can move to different configurations ( ex : Mazda global powertrain boss Mitsuo Hitomi says the rotary is likely to return as a range extender engine to generate power for an upcoming EV on longer journeys, according to Automotive News. ) There can be lot more configurations of ICE can be used ( ex : http://www.libralato.co.uk/technology/index.html ) because there are considerations on size, weight, number of parts, efficiency etc.



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