I read about Smokey Yunick trying this in the 70’s with mechanical timed fuel injection. Basically, 2 pumps turned by the engine and timed to the cylinder. One injector at the top of the intake tube timed just a little earlier than a second one right in front of the valve. With a sequential electronic fuel injection, you could adjust the time of both sets of injectors to accelerate the mixture to “supercharge” or pulse charge the cylinder. I.e. greater than 100% volumetric efficiency without a turbo or supercharger.
I’ve only heard or read about this on race engines but it seems like it could work (and may be working) on street engines. Add that to the 50 (!!) degrees cam timing adjustment (like my Mustang Coyote engine) and that combo could explain some of the horsepower gains we keep seeing.
Interesting, I’m curious whether the mixture ignites all at once or the flame travels from one part of the mixture to the other. The promise of the HCCI hype is fast and low temperature burn
I think it uses the theory that ignition occurs in the area of proper A/F ratio and propagates the flame front to the lean areas. This is really a stratified charge type combustion. The cooler burn of HCCI to reduce oxides of nitrogen can be achieved other ways - EGR for one and catalytic convertors for another.
There is a young man who comes to visit a neighbor, just the other side of our avocado trees. He has an old 60’s Nova, a lovely black thing and he is very proud of it.
I don’t know what year it is, but at first glance it looked much like the 67 Chevy II I owned back then
I have a BBC engine I designed back in my day that is naturally aspirated and calculated to achieve 108% VE by maximizing pulse charging. I had to leverage the skills and tools of the mechanical engineers working for me to model the various bits. I could then try various modifications in simulation to see the effect of smoothing here, material reduction there, valve timing and opening volumes, intake and exhaust restrictions etc. Pretty complete model when it was done. I still recall some verbal battles with various people regarding effects of exhaust back pressure being CRITICAL to maximizing VE (too much scavenging no good!) because of this misguided belief that you can’t have too big of an exhaust pipe (dude, you’re choking off that big block! No I’m not…). Anyway, it was an eye opening exercise…
Agree with your experiences. I am of the school of big pipes with lots of resonances. A cam lift, cylinder head and carb restricted 400HP 350 Chevy V8 race engine I built used tri-Y headers merged into a single 3.5 inch exhaust. The 3 different resonances (8 into 4 into 2 into 1) added 50 ft-lbs over shorty headers merged into a single 3.5 pipe with 2 resonances (8 into 2 into 1) That back pressure argument is poppycock!
Resonances cheat the volumetric efficiency and can get you lots of “free” power.
It’s amazing to me that now engineers design their ideas on a computer screen and then test run them using that computer, all sort of abstractly, before anyone picks up a welding torch or a grinder. @TwinTurbo and @Mustangman, it sounds like you guys did a ton of hard, detailed manual labor in your research, which took a lot of time, and now people are doing all that in a couple of hours, on a screen. Routine production cars are getting far more power per cubic inch, and using less fuel, than anything that could be done even 10 years ago.
While I’m much more interested in coding a computer than physical experiments, gathering experimental data is vital before embarking on numerical simulation.
Before numerically testing your new design in a computer, you need to perform small scale, simplified experiments to gather some physical data. Then you create a numerical model in which you choose details that might be important to include. Ensure your numerical results closely matches the physical results before testing your new design on a computer. Otherwise, it may be garbage in, garbage out. The worst part is you won’t know your result may be complete crap.
As a side note, the engineers working on the movie Shrek took a mud bath before coding that opening scene
The data regarding modeling internal combustion engines has been gathered continuously over the last 100+ years. Now supercomputers can solve the fluid dynamics in 3D, allowing accurate simulation of the combustion process.
There are lumped parameter engine models that also do a credible job that run on any PC. That’s what I used to model my race engine and I included the resonances in intake and exhaust. CFD would have been useful to improve the exhaust modeling but the lumped parameter model was close enough.
Actually, the modeling and empirical testing are an iterative process that repeats almost indefinitely depending on how accurate you want/need your model to be. In my experience, we start with simple models and then perform experiments to confirm the modeling assumptions. Then it’s lather, rinse, repeat.
The old saying- what do all models have in common? They’re all wrong…but some are useful.
I find the youngest engineers are the ones that rely far too much on their modeling information and tend to get burned the worst because of it.
I agree with your post and that’s why I’m not in engineering. My classmates wouldn’t share my sentiment, but I enjoyed the math more than the science when I was in engineering school. One of my favorite class was numerical methods.
A career in engineering mathematics would lead to research and I don’t want to beg for research funding. I found my happy place in software development
that is naturally aspirated and calculated to achieve 108% VE by maximizing pulse charging. I had to leverage the skills and tools of the mechanical engineers working for me to model the various bits. I could then try various modifications in simulation to see the effect of smoothing here, material reduction there, valve timing and opening volumes, intake and exhaust restrictions etc. Pretty complete model when it was done. I still recall some verbal battles with various people regarding effects of exhaust back pressure being CRITICAL to maximizing VE (too much scavenging no good!) because of this misguided belief that you can’t have too big of an exhaust pipe (dude, you’re choking off that big block! No I’m not…). Anyway, it was an eye opening exercise…