Gasoline vs Diesel - Which Is Best?

What is the difference between gasoline and diesel engines? The difference between the gasoline (Otto) cycle and the Diesel engine cycle. A look at thermodynamics and how these cycles are different. The main difference is the fuel injection stage, as this occurs after compression in Diesel engines.
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[@EngineeringExplained]

Yes, actually I would head to my website where I've organized it a bit better. The link is in the description; start with lesson 1 and keep watching till you no longer care about cars anymore. :)

[@rhinorampage1807]

Dude. Your a great teacher. Very knowledgable. Thanks for sharing.

[@kyphilburg]

I love how much inner turmoil he was going through when the diagram was still labelled Otto and when he almost drew a graph without labelling the axes.

[@EngineeringExplained]

Glow plugs are typically used for starting only. Diesels known as CI engines (compression ignitions).

[@biggee9266]

Hey man how did you learn all of this? You should seriously consider becoming a professor! These topics aren't easily explained clearly and you do a great job of translating it to the average person.

[@Piercebelton]

Wow, I am thoroughly impressed! I just finished watching all of your forced induction and suspension videos , and I've learned more in the last hour about cars than I have in the last year. Thank you for making everything so crystal clear and concise. Keep doing what you're doing, I think it's amazing.

[@EngineeringExplained]

Yes, check out the FAQS on my website (link in the description) and I've listed some recommended books.

[@EngineeringExplained]

@Hondaminican If I said cycle, I meant engine. Diesel engines are more efficient since they have higher compression ratios, and diesel fuel is more energy dense.

[@51wisley]

Well explained, I did not understand how a diesel engine worked before your excellent tutorial.

[@artao5]

Dude, you explain this stuff SO fricken well!! Thank you. =D

[@EngineeringExplained]

Thanks for watching! :)

[@EngineeringExplained]

Check out my "Learn how cars work" playlist (second one down on my channel page) and work your way through sequentially. You'll learn it all in no time!

[@EngineeringExplained]

Check out my video "DOHC vs SOHC vs OHV." I will also have another coming somewhat soon.

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[@EngineeringExplained]

lylesification Thanks for subscribing!

[@kavb970]

Why can't gasoline engines compress air alone first the same way diesel engines do?

[@IlhamDefraN]

+Kavin Bakhda u mean its like direct injection engine? the fuel are injected directly inside cylinder at the same time air are sucked.

[@im11.13]

+The real doktorbimmer so what is the advantage to still use diesel rather than gasoline if gasoline permits the same efficiency than diesel?

[@frodobaggins3974]

Technically they can. The problem is that gasoline and diesel oil have very different flash points - gasoline would spontaniously explode long before the piston finnished the compression cycle, which would damage the engine (you don't want uncontrolled explosions there - hence the spark plugs). So there is a pressure limit to which you can compress gasoline. With diesel this problem does not exist, which allowes the engine to operate at higher pressures, deliver better fueal economy and reduce the amount of heat.

[@Befindox7]

Not hot enough

[@nicholaspappas101]

Mazda is working on this!

[@EngineeringExplained]

Let me know if you have any questions.

[@EngineeringExplained]

Thanks for watching!

[@timbruse]

What gets the piston moving in step 1 when there is no combustion yet?

[@InZomnia365]

When you start the engine, the electrical starter does it, from then on the engine runs itself. When one cylinder is doing intake (1) another is delivering the powerstroke (3) which rotates the crankshaft (which is what makes the intake-stage piston move).

[@timbruse]

Got it. Thank you! Do diesel engines provide for better fuel economy than Otto?

[@timbruse]

Also, if I understood correctly, in a diesel engine, during the compression stroke, the gas is compressed (not fuel mixture gas) until it is heated to the point of combustion from compression itself? Are the spark plugs like in an Otto engine to ignite it?

[@dtps238]

Tim Bruse From the compression itself. Diesels use glow plugs, not spark plugs. Diesels do their power stokes through compression, which is why in turbo diesels you'll see them "run away", commonly caused by a seal going bad on the turbo, and this in turn sends the oil through the intake, and since the compression is so high, it can eat itself to death via oil.

[@JoshuaZiesmer]

doktorbimmer every diesel I have ever operated had glow plugs including agricultural equipment. Cumins diesels have them in the air intake manifold instead of the cylinder.

[@zackjohnson1781]

So diesels have no spark plug?

[@samuelmoyen3629]

Zack Johnson im asking the same question

[@dannyman1k]

That's right, the temperature is enough for combustion

[@z28punisher42]

Zack Johnson no. The hot compressed air will do the job

[@EngineeringExplained]

@doktorbimmer Correct. Honestly I didn't expect this video to be very popular, and didn't include many differences. I just wanted to get the main point that one is ignited with a spark, and the other uses compression for combustion. But yes, diesels adjust amount of fuel going into the cylinder for power, gasoline engines adjust the amount of air.

[@EngineeringExplained]

Glad the information was useful for you, and I appreciate anyone who shares my channel!

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10 years later and i still love this guy, absolutely amazing

[@EngineeringExplained]

Thanks! I'm a mechanical engineer. I've got more "about me" info on my website if you're interested. See the video description.

[@EngineeringExplained]

Thank you! Really appreciate your views!

[@EngineeringExplained]

@cadetAJ18 Uh possible RWD vs FWD, torque steer, PDCS. Voting is on facebook, search EngineeringExplained.

[@EngineeringExplained]

Glad you enjoyed the video, thanks!

[@EngineeringExplained]

Thank you sir, means a lot to me! Glad you find them helpful!

[@EngineeringExplained]

@awesomeness2571 For cold starts a glow plug is used. It heats inside the combustion chamber, and with the added heat from compression, the temperature is great enough for combustion.

[@johnybrokeit]

cant wait to see what this glow plug looks like and where it is situated in the cylinder or whereabouts.

[@EngineeringExplained]

You're welcome! Glad you like them.

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No unnecessary Intro and Outro! Well explained and straight on point! Subbed after watching just 3 videos.Gonna watch your complete different playlists.

[@EngineeringExplained]

@lukeplusmusic Thanks, good to hear!

[@makismakiavelis5718]

Thank you for that video! I can't believe i just now learned how a diesel engine works. I always stupidly assumed that the cycle was the same as with gasoline engines and only the type of fuel changed. So in diesel engines you don't need spark plugs at all, the fuel instantaneously ignites on "touch" with the highly pressurized and therefore hotter air... that's fascinating.

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Your simplicity is refreshing. Many technical YTers waste viewers time. Good job !

[@EngineeringExplained]

Happy to hear it, thanks for watching!

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[@EngineeringExplained]

Correct, and sometimes it's even manipulated to spray more than once, btdc, tdc, and even sometimes after - as I'm sure you already knew - nice to point out though, thanks!

[@EngineeringExplained]

It varies. Some have it during both phases, compression, at top dead center, and during expansion. And it can be manipulated depending on how hard you press the gas pedal.

[@EngineeringExplained]

Good question, I don't know of one though it's probably out there somewhere, would be interesting to see.

[@EngineeringExplained]

Glad they help you!

[@EngineeringExplained]

@bloximonkey Do they? Different applications, either choice could be a viable option. I wouldn't say gasoline has higher performance. They can hit higher rpms, since they use lower compression ratios and typically lighter materials, and many times smaller engines, but there's a diesel that can match the specs for most cases.

[@EngineeringExplained]

I agree completely. Eventually I'd like to make a video on the advantages. I'll get there someday.

[@EngineeringExplained]

That would be a good topic and easy to explain. I wish I still had my white board with all the clutch material on it. Basically, the engine isn't producing enough force to actually move the car forward, so when the clutch engages the engine to the transmission, it just shuts off since there isn't enough force to move it forward (and keep it moving). Perhaps eventually I can make a short video describing the entire process.

[@EngineeringExplained]

Yes, check out my video "compression ratio and thermal efficiency"

[@EngineeringExplained]

@cadetAJ18 Yes, you are correct. No need to say please haha! Though some gasoline engines (especially newer ones) use direct injection, in which the air is compressed without fuel and it is sprayed in at different times to optimize power/efficiency.

[@EngineeringExplained]

@doktorbimmer Yep. I took an internal combustion course at my university. I believe the A/F mixture for gasoline was around 14.6 ideally (+/- 0.5) and for diesel the range was something like 18-70. 70 being idle with very little fuel consumption, 18 being with the pedal down. Our professor also said that stoichiometric for diesel is around 15:1, but is rarely used. I found that interesting.

[@EngineeringExplained]

Good question and something I don't have a great answer for. I do know that most diesel engines can fairly easily use quite a range of fuels (with some simple modifications, if needed), so it may be possible that it ran.

[@EngineeringExplained]

That's a fascinating question, and something I haven't quite figured out. Apparently they're able to reduce friction, and the weight of the components, and this has paid off with fuel economy. I don't know all the details; I'm curious about it as well.

[@skinman620]

These are really great videos. Thanks for posting. You are an excellent teacher: able to explain things thoroughly in a way that is easy to understand. I watched your turbo charger video the other day ahead of the new f1 season and it was excellent. Can you explain the role of glow plugs in Diesel engines? Thanks again for your videos.

[@kylerichmond7734]

Fantastic video! I am going to go to school for Mechanical Engineering in the fall so I am trying to broaden my knowledge base. In this short time of watching the video I learned a whole new concept of power. Keep the videos coming! You explain everything very clearly and make it very simple to understand! Mind blown! Thanks!

[@tombotification]

Very easy to understand and helpful video. I was just analyzing the properties of the cetane number and the octane number and this video explained their different field of application (diesel and gasoline engines). Thank you very much!

[@EngineeringExplained]

The crank rotates twice for every four strokes of the engine. Thus you can use the rotations of the camshaft (1/2) to calculate the number of strokes per second. 6000/2 = 3000 (RPM of the camshaft). 3000/60 (seconds in a minute) = 50, so 50 times per second.

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[@lekash]

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[@EngineeringExplained]

@jcnbw01 Yes, exactly.

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[@EngineeringExplained]

@techno1246 Yes, I was actually planning on doing that this week! Thanks for the tip!

[@infokemp]

@EngineeringExplained - Excellent video. All the best David

[@EngineeringExplained]

There is no opening for the pressure to be lost. And the injected fuel is at a much higher pressure than inside the cylinder. What opening are you referring to?

[@EngineeringExplained]

It's a good question, and it has been done. It simply isn't as efficient. I believe the mixture doesn't occur as well, and it's a bit less predictable.

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[@EngineeringExplained]

The momentum of the flywheel, which is there due to the power from previous power strokes, and current power strokes if the engine has multiple cylinders.

[@EngineeringExplained]

Thanks Ben!

[@EngineeringExplained]

Search "fuel injection" on my channel page. Should help you out!

[@aaronrivers64]

Good video. Very thorough explanation without being over technical.

[@EngineeringExplained]

Awesome, thank you!

[@SuperSonicSpeedGuy]

I still love watching your videos, learn something new every time! I'm training in a garage to be a mechanic when I'm older so the more info I learn, the better! Thanks for the brill vids keep up the great work :-)

[@EngineeringExplained]

+SuperSonicSpeedGuy Thanks, best of luck to you!

[@SuperSonicSpeedGuy]

+Engineering Explained Thank you :-D I'm honoured that you've replied:')

[@EngineeringExplained]

@brakehorsepower1 Just starts. Once the engine heats up it's not needed.

[@mcrsit]

Nice tutorial! I'll watch the entire series!

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Your channel is amazing, I have gone from knowing very minimal things on cars to knowing A LOT.

[@EngineeringExplained]

Thank you, glad you've found it beneficial!

[@EngineeringExplained]

@cadetAJ18 What? Umm, gasoline uses a spark for ignition, diesel uses compression. Is that what you're asking?

[@EngineeringExplained]

You could, yes. You would need to rework the top end to make up for the spark ignition, but it can be done.

[@EngineeringExplained]

Correct, glow plugs are just used to help heat the initial strokes to start the engine. Compression does the rest.

[@EngineeringExplained]

It's a great question, and a great mystery as to why we just can't seem to latch on to the diesel "train." in America. It's more efficient, more durable, and cleaner. Yet some states tax it more, and people think it's dirty and inefficient.

[@EngineeringExplained]

Your second question answers part of your first question. Horsepower is relatively low because the engines are low revving (see my video on hp vs tq). Diesels have more torque because they use higher compression ratios, typically are turbocharged, and have a longer stroke. The high stroke is part of the limitation of the RPM, as combustion can only occur so quickly. I have videos on compression ratio, turbos, and average piston speed (stroke/combustion) if you would like to know more.

[@EngineeringExplained]

Yes, if it asks for premium you should use premium. You should always use the recommended fuel. The possible consequence of using lower grade fuel is pre-ignition in which your cylinders may fire before the spark plug fires. This can very easily damage your engine if it occurs. Many companies have built in failsafes that prevent this from happening so when people use the wrong fuel grade the engine doesn't break, but that doesn't mean the risk isn't there.

[@EngineeringExplained]

The energy density isn't as important as it sounds, the compression ratio plays a much larger role than you may think.

[@jameswiblishauser9745]

great video, broke the process down so that even I could understand it, and that's not easy. much thanx

[@EngineeringExplained]

@maxime0999 I've still got plenty to learn!

[@EngineeringExplained]

Great, thanks!

[@EngineeringExplained]

@G30RG3walker Diesels have glow plugs for cold starts, just to heat the cylinders a bit on top of the heat generated from compression. As far as the fuel type, I'm not positive, but I would assume diesel is more predictable as far as auto-ignition, in the sense that at a certain temperature combustion will occur.

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You are so awesome, sir. Thank you for taking your time making these videos and helping dummies like me understand how stuff works.That's all.

[@EngineeringExplained]

Yes, the pistons push down, and connecting rods rotate the crank. Probably best for you to check out my video "engines - explained" which should help clear things up. The power stroke powers the other strokes, yes.

[@trungtube]

Nice job explaining. Very easy to understand!

[@EngineeringExplained]

Well it would be based on the ambient temperatures, and then you could use PV/T(1) = PV/T(2) to find the increase in temp from the increase in pressure.

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[@gerrardvahmedoh]

Hey!!! Thank you for this video it was the most clearly explanation I've found.

[@jundialhaqiqa9907]

Very helpful, I never studied diesel engines in school, so this helps me understand them much better.

[@EngineeringExplained]

In a sense yes, you can look at injection of diesel as very similar to ignition timing on petrol engines.

[@thatsjusthim]

Very clearly explained and easy to understand, great tutorial.

[@EngineeringExplained]

Thanks, you're welcome!