Jeep's New Hurricane 4 Engine Is Insane!

One of the most technically advanced four-cylinder engines ever just launched. This engine has a passive pre-chamber with turbulent jet ignition just like what is done in Formula 1. So, it can make both loads of power without using much fuel. It uses two spark plugs per cylinder. It's running the Miller cycle. It uses plasma spray cylinder liners, dual fuel injection, electric cam phasing, and a variable geometry turbo with up to 35 PSI of boost pressure. Oh, and it's made by Jeep. Yep, the first company making modern F1 engine tech mainstream is Jeep. I did not have that on my bingo card, but maybe I should have considering Maserati in the same Stellantis family as Jeep introduced this tech to production cars with the MC20's Natuno engine. But it is Jeep that will bring this tech to mainstream pricing. Now, at this exact moment, history nerds are furiously typing, "Um, Jason, Honda was making pre-chamber engines in the 1970s. Go on, get it out. Feels [sighs] good, doesn't it? Okay, this is quite different. We're moving on. All right, so I had a fascinating chat with Jeep's engineering to learn all about this Hurricane 4 engine. And so we're going to dive deep into understanding how it works, starting with a quick review of how turbulent jet ignition works. All right, so like any four-stroke gasoline engine, we start things off with our intake stroke, pulling in air and fuel. In this case, we are using port injection as well as direct injection for the fuel. Then we of course have our compression stroke. So, we compress that air and fuel. Some of that air and fuel goes within this little pre-chamber, which Jeep was kind enough to send me one to check out. And so, then we have our power stroke. So, our spark plug within this pre-chamber ignites the air and fuel mixture within that, which shoots out these turbulent jets as that combustion occurs that pour out into the main chamber. And so as these turbulent jets shoot out into the main chamber, you have very fast, very complete combustion. This reduces the likelihood of knock. And because of that, you get more power and you get better efficiency. So looking at the specifications of Jeep's engine here, the Hurricane 4. This is a 2 L inline 4 turbocharged engine. It's producing 324 horsepower and 332 pound- feet of torque. It is using a variable geometry turbo and it has a max boost pressure of 35 PSI. Yes, that is gauge pressure. Yes, it is bonkers high. And it is using a 12:1 compression ratio, which is quite high for a turbocharged engine. Now, when you start to think about designing this little pre-chamber, there are a lot of variables that come into play. So, you have to think about the surface area to volume ratio. number of holes. In this case, there are eight radial holes and one central hole. You also have to think about the diameter of these holes. So, in this case, Jeep is using about 1 millm holes for the radial ones. And then the one in the center is about half a millimeter. Now, why would you have different size holes? Well, you need to think about the energy of these jets. The energy that's going to come pouring out of these jets. So, if it was too high, much energy coming out of these jets and it was pointed directly at your piston, you could literally melt that piston. So, you really have to think about this design. You have to think about the angle that you have and the size of those holes, right? If you go too small, you're not going to have quite as much energy. It's restricted. Or if you go too big, it's not going to have quite as much energy. You have too much space, right? And so, it's kind of this perfect center spot of where do we get this to ensure that we have the ideal combustion characteristics we're looking for. Now, as far as why the center hole is smaller than the radial holes on the pre-chamber, we're looking at the distance that flame has to travel. Right? So if your piston is right underneath this pre-chamber, you don't want a really strong jet just blasting right into it. So you use a smaller hole in the center of the pre-chamber and then where you have a further distance to travel in the main chamber then these radial holes are larger so they have more energy in those jets. Now you might wonder how do they ensure these pre-chamber holes don't clog up with carbon deposits. Two comments. First, remember every time we have our compression stroke, we're pressing air and fuel back into this pre-chamber. So, you can benefit from the fuel's cleaning properties as it goes into the pre-chamber. But second, and more importantly, the temperatures in this pre-chamber get so hot, you literally just burn everything off of it. So, it's something you are designing for, but ultimately something Jeep says is not an issue. This portion of the video is sponsored by Motive, who sent me their AI dash cam plus. This advanced dash cam is designed as a safety and operations aid packed with useful features for use in fleets. For example, two front-facing cameras provide stereo vision. This

enables precise forward collision warnings. The front zoom lens supports automated license plate recognition, capturing evidence in the event of a hidden run. Sensor Fusion combines sensor data to record important events. Say it hears the sound of broken glass. It knows to record in case of a vehicle break-in, and it can provide prompts to the driver to help save on costs, for example, if the engine is unnecessarily idling. And helping enable all of this is a powerful processor that can handle over 30 precise AI models simultaneously, ensuring critical moments are captured accurately in real time with minimal latency. To learn more, check out gomotive. com/dashcam or hit the link in the video description. Now, this engine is running the Miller cycle, and it is doing so by closing the intake valve early. So, what does that mean? Well, as the piston is on its way down during the intake stroke, you are closing that intake valve before the piston reaches bottom dead center. So, you're closing that intake valve early, and then the piston is still traveling downward. Why do you do this? Well, it improves efficiency. How? Well, one of the ways is it increases your expansion ratio versus your compression ratio. Another thing that it does is it reduces your pumping losses. So, let's look at a low load example. Let's say we're at partial throttle. We're trying to make a little bit of power. And so, during this, we're going to have a short cam duration. This is Miller cycle all the time on this engine. It is always running early intake valve closure. You do have variable cam timing, but it's always going to be closing that intake valve early. Now, what happens is you close it early, and so that means you have less time to fill up this cylinder. Well, if that cylinder, that means you have to open your throttle a little bit more in order to get sufficient air in it. So, the more you open the throttle, that reduces your pumping losses. So, you're forcing the engine to operate at a higher throttle than it normally would have to. And in doing so, that improves pumping losses. Amazing. Now, by running the Miller Cycle in combination with TJI, this means we can run a higher compression ratio. Again, 12:1 for a turbocharged engine is quite high, especially considering how much power this is making. And overall, that higher compression ratio means we get better efficiency. And that really gets into the heart of why this engine is so impressive. It isn't simply because it makes a lot of power. And don't get me wrong, 324 horsepower is a lot for a mainstream mass market 2 L, but there are some niche 2 LERs out there making more power. What makes Jeep's engine so impressive is not only does it make a boatload of power, but it does so very efficiently. And so this brings up BSFC or brake specific fuel consumption. All right. So brake specific fuel consumption is a ratio of how much fuel do you have going in versus how much power is coming out. So the lower the number the better because that means you're making more power with less fuel. So brake specific fuel consumption here you have the math if you're curious where the units come from. You have your mass flow rate over your brake horsepower. That's grams per hour over kilowatts or grams per kilowatt hour. So we're looking at a graph here of our brake specific fuel consumption versus how much power our engine is making. And so this is like a big scatter plot, right? And I could take an engine and say if this engine is making 100 kows of power, what is its efficiency that it's operating at? And then you would get a little point on this plot right here. And so if you do this for all the four cylinders out there, a lot of the mainstream four-cylinders out there, which Jeep did, and they provided this plot, you can get this range that you can see these four-cylinders tend to fall within as far as their brake specific fuel consumption versus how much power they're making. And what's really impressive about Jeep's engine is that it basically just traces the bottom line of this plot. So it means it's as efficient as possible compared to today's modern engines in terms of efficiency for making a certain amount of power. All right, let's look at this plot and just grab an example to get a bit of a better understanding of it. So let's say we want to understand what our brake specific fuel consumption is when our engine is producing 100 kW. So we just go to this line right here and that's our point. And so that gives us based on this plot that Jeep provided about 211. 5 grams per kilowatt hour as far as our brake specific fuel consumption. So how do we convert this into thermal efficiency so we can understand what that number means? How efficient is this engine really? Well, efficiency power out divided by the energy that you're putting in the rate at which you're putting in energy or one over our brake specific fuel consumption multiplied by the lower heating value. We do the math right there and that gives us an efficiency thermal efficiency for this engine while producing 100 kows of power of about 40. 5%. Now there are a couple assumptions that go with this assuming that plot is accurate and then assuming the lower heating value of gasoline mixed with 10% ethanol is about 42 mega per kilogram.

But this number right here 40. 5% is very very good for a gasoline engine. It is incredibly efficient And just to further reiterate how impressive what this engine is doing is, it's using 10% less fuel while making 20% more power than Jeep's 2 L turbo they're currently using in the Wrangler. And versus the Jeep Grand Cherokee using the 3. 6 6 L V6 engine. This has more power, more torque, better fuel economy rating across the board, and it's about a full second quicker 0 to 60. It's just better. Okay, so now let's move on to why it has dual spark plugs as well as dual fuel injectors. Starting with the plugs. All right, so let's get an understanding of the overall layout. If you were to shrink yourself down and stand on top of this piston and look up at this cylinder head, you would see, of course, your two intake valves, your two exhaust valves. Then there in the center you would see the pre-chamber and of course housed within this pre-chamber is one of your spark plugs. You also have another spark plug that is firing for the main chamber. Then you have a direct injection here on the left and you also have port injection. So two fuel injectors, two spark plugs. Why do you use two spark plugs? Well, a couple of rules here. We're going to look at a plot of torque versus engine RPM and see when do we use each of the spark plugs. But a couple rules. First of all, the pre-chamber spark plug is always firing. Second of all, you always want some stagger between when you fire one plug and when you fire the other. That's because you want to have some leading form of combustion. something predictable. You want to, you know, choose what mechanism do I have that is igniting this air fuel mixture. You're not firing both at the same time and then having them battle it out. So, you're always going to have the pre-chamber firing, but when it fires differs, and you want to make sure that these fire at different times. So let's work in some of the scenarios. If we're at a low load here and you know various engine RPM or you're heating up your catalyst for example, well then you're going to have the main chamber lead and so at these low loads you don't have a ton of air and fuel in this mixture right in this chamber that's all mixed up. So and it could be inconsistent and you're relying on that mixture getting inside of this tiny little pre-chamber and then hoping that you have consistent combustion. So because of that, you just use the main chamber spark plug to fire it. Then shortly after you fire the pre-chamber spark plug. That gives you better consistency, better catalyst heating, and you don't have to worry about the emissions aspect of the consistency of that pre-chamber firing. Now, as you start to get into higher loads, then you start to have plenty of air and fuel mixing and you have plenty get within this pre-chamber, so it's no worries. And then you have the pre-chamber leading and then shortly after you have that main spark plug for the main chamber firing. And so the main mechanism for igniting the mixture of course in that scenario is the pre-chamber rather than the main chamber plug which we had at lower loads. And finally we get to the high load scenario. So when you're trying to make as much torque as possible, you're just using the spark plug within the pre-chamber to ignite that air fuel mixture. You are not using that main plug at all. So why? Well, there's a couple of reasons for this. Remember, one thing that we always have to do is have some delay between when one spark plug fires and when the other fires. But at these really high torque scenarios, we're having this air fuel mixture ignite very quickly. And so, if you have just a small delay, well, it means you've already got really high heat and really high pressure within the cylinder. And then this spark plug is firing against that really high heat and really high pressure. And so because of that, it actually reduces the life of that plug. It's not a great scenario to have that plug igniting. And so there's minimal benefit, first of all, because the pre-chamber is going to do a great job of igniting all of that air and fuel mixture. And then second of all, you can damage your main plug if you have it igniting in these really high temps and really high pressures. So no reason to use it in that scenario. So it is just reliant on that spark plug within the pre-chamber. All right, moving on to fuel injection. Why are they using both port and direct injection? So, we're going to look at a similar plot here of torque versus engine RPM and just work through some of the scenarios. When you first start up that engine, so you want to heat up your cat. That's the most important priority. Well, then you're going to be having late combustion and in doing so, direct injection gives you better control. So, in that scenario, they're going to be using more direct injection, less port fuel injection. Then once your engine is warmed up and you're just idling or at very low loads, then you're just going to be running with port fuel injection. Port fuel injection is at a much lower pressure. As a result, you don't have to hear that direct injection pump. And so the engine runs much quieter. So when you're just sitting there idling at a stoplight or at a stop sign, whatever it may be, the engine will be really quiet while using just port fuel injection. And as you get into your highest loads, you start to become more dependent on direct injection and less dependent on port fuel injection. And that's because direct injection improves the knot

characteristics of combustion and so you can have more power and more power at greater efficiency. So there's a lot of innovative technology used on this engine. And on the subject of innovation, Porsche launched a new 911 turbo in 2006, which was the first time a gasoline production car used variable geometry turbos. And now 20 years later, we get to see that tech make its way down into mass market engines. How cool is that? All right, so a quick review of how variable geometry turbos work. So within the exhaust portion of the turbocharger, you have these veins and these veins can open or close. And so as you close them up, you're creating restriction. And so by doing so, you're speeding up those exhaust gases and thus you're going to spool up that turbocharger very quickly as the exhaust velocity is very high. Now that is at the cost of reducing your exhaust flow. So if you want to reduce the restriction in the exhaust, you open up these veins. And so then it acts much like a large turbo rather than acting like a small turbo. And so in this case, you have less energy going into spooling up that turbocharger. And in fact, you can use variable geometry turbos. I did not know this. You can use them without waste gates because you can essentially just use the direction that the veins point towards in order to determine how much boost you set. So you don't have to rely on a wastegate to bleed off excess pressure. They still do use a wastegate in this scenario on the Jeep engine, but it is purely for heating up the catalytic converter. So when you just start off the engine, you have that wastegate fully open. You bypass [clears throat] your turbo essentially and have that exhaust just go straight to the catalytic converter rather than putting energy into the turbo. So there is a wastegate, but you don't need it at these high loads. In those cases, you just open up the veins fully. If you were to open them fully, you're basically just going to have so much exhaust flow that you're restricting the speed of that turbo and thus your boost comes down. Now, I mentioned this engine has a peak boost pressure of 35 PSI, which yes, is bonkers high. But there's some context that you need here because that is the peak pressure that the engine will ever see. That is going to be very, very rare that the engine would actually be running with that much boost. First of all, because you're not always flooring it. But second of all, let's say you're at sea level and it's cool ambient temperatures, you don't need 35 PSI of boost to make that 332 lb feet of torque. So as you start to go into higher elevations where the air is thinner or as temperatures really climb up and again you don't have as much oxygen going into the engine, well then you can compensate with this engine by increasing the boost. And by increasing the boost, you make more power. So at sea level, cold temperatures, no, you're not going to be hitting 35 PSI. That is the peak in scenarios where it can't otherwise make the desired torque output. Now, I just want to close out with a fun anecdote because when I was in college, one of my roommates had a Jeep Cherokee XJ, which had a 4 L inline six-cylinder engine that made 190 horsepower. And here we are with an engine half that size, making 70% more power. I mean, this is quite cool. Another example, my other roommate, I guess they just like Jeeps, my other roommate had a Jeep Grand Cherokee, which had the 4. 7 L V8 engine, a V8 engine, which was making 235 horsepower. So, this four cylinder is making nearly 100 horsepower more than the Jeep Grand Cherokee uh back in the early 2000s with the 4. 7 L V8. Unreal. And for those wondering, yes, this new engine has the structural enhancements to handle the additional power. And worth mentioning, even though this is making a lot of power per liter, it's still significantly lower power per liter than its relative in the Maserati MC20, which is also using TJI. The Jeep engine is focusing on efficiency as much as it is focusing on power, and it does a great job at both. Crazy. If you have any questions or comments, feel free to leave them below. Thanks for watching.