Alehander's HCCI Thesis Project

Biodiesel, Dual Fuel (Diesel/Propane, Diesel/NG), HCCI
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Frank
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Alehander's HCCI Thesis Project

Post by Frank » Thu Mar 08, 2007 9:16 am

This is a continuation of his HCCI posting on the Lets get this one started! thread.

Alehander did some very interesting research while a student at California Polytechnic State University. His thesis is entitled COMBUSTION TIMING CONTROL OF HOMOGENEOUS CHARGE COMPRESSION-IGNITION (HCCI). The goal of the thesis was to establish control over (auto) ignition timing of a VW TDI engine running on gasoline... by using water injection at the intake manifold. Gasoline was probably the wrong fuel for PING/HCCI, in retrospect. With a much lower octane rating, the autoignition timing advanced wildly; CNG or LPG would do much better - he believes Stanford had a team of MSME students working on CNG HCCI at the same time.

He had lots of fun, but liquefied the pistons before any appreciable amount of data could be gathered. I hope it wasn't his car's pistons.

I'm interested to learn more about the background to this project like why he chose this project, the fuels used, and the engine.


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Post by alehander » Fri Mar 09, 2007 9:50 pm

Hey, Frank. Here's some background on my work at Poly:

As a graduating BSME student and having been accepted into the MS program, I had 2-3 months to find a thesis topic, money and a commitee of profs willings to advise me. None of my own ideas stuck, and one of our ME automotive clubs, FutureTruck, was looking for a competitive drivetrain. FutureTruck was an OEM-sponsored competition to take a factory SUV and double it's mileage while improving emissions. The adviser of the CalPoly FutureTruck team was sold on HCCI; dieseling on gasoline/CNG was supposed to produce the economy of a diesel with none on the pollution. He recruited me and two more grad students to convert a VW 4-cyl TDI for HCCI operation. The other's work consisted of the actual hardware conversion; my job was to stabilize combustion timing. Dieseling on gasoline was stable only below ~2500RPM and without a load; the engine also sounded like jackhammer.

The engine got an aftermarket gasoline TBI system from Injection Logic, a local EFI company where I worked briefly after graduating. I built what was essentially a second multi-point EFI system with manifold-mounted injectors; this system ran the water intended for combustion timing control. I also modified the glow plugs to detect the combustion events themselves. The idea was to detect (auto) ignition, determine just how advanced it was and inject the correct amount of water to retard combustion to some reasonable value. Sounds easy enough...

None of us new enough about IC engines in general, unfortunately. The system was built and tested with some minor blowups - diesel engines do NOT like uncontrolled amounts of water and gasoline! The engine had to be started on diesel and warmed up to operating temp. The diesel was then throttled back and the gasoline TBI system came online (this is where we put in the ear plugs). This procedure in itself was a major Hail Mary - none of use know enough to look at AFR, CO or even EGT to maintain a reasonable diesel/gasoline/air balance! Long story short, during one of these fuel switcheroos we must have swung way lean... and the rest is history.

From the limited data set we gathered, water injection did have the desired effect of retarding combustion of HCCI. We did not, however, manage to build a water "fuel map" for that engine or determine just how effective this method would have been at high load/rpm.

This project made for a very anticlimatic thesis defense.
Lenin zhil, Lenin zhiv, Lenin budet zhit'

Frank
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Post by Frank » Mon Mar 12, 2007 11:30 am

That sounded like a fun thesis, even if it didn't have a commercially viable concept. We had a list of thesis topics at Ottawa U and I picked one about flame propagation. While not all that anticlimactic, it also wasn't very memorable.

Incidentally, Diesels normally run lean. I can see too much fuel with too low of an octane rating causing a diesel engine to melt-down. Is it possible that you went over-rich when you switched to gasoline?

Anyway, I'm looking forward to reading about your next project.

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detonation

Post by franz » Mon Mar 12, 2007 11:46 am

The detonation pressure waves created by using gasoline, even with a water injection, caused localized hot spots and metal deformation. On a gasoline engine with a detonation or pre-ignition problem can cause a piston to disintegrate. I have seen pistons blow apart in as little as 10 seconds from normal operation to seized engine.

In the early 90's, I was working at an engine lab developing a lean burn fuel system on a popular inline 6 cyl 5.9 liter spark ignition converted diesel engine. We were running about 2800 rpm's at around 30 psi boost, making somewhere around 245 bhp. Exhaust temps were around 950 deg F, and around 1.8 Lambda. Within 10 seconds, the engine went from sewing machine smooth to a loud rattle, then silence.

An analysis of the roto-chart showed a spike in the exhaust temps to 1500 deg about 5 seconds before the engine popped. A mechanical inspection showed nothing amiss, but when we did a gas rotograph of the fuel, we found an Ethane spike (we were running natural gas on pipeline). When this engine was so finely tuned for that specific caloric value fuel which was diluted with a fuel with a totally different caloric and octane value, it didnt stand a chance.

Franz

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Post by alehander » Mon Mar 12, 2007 12:19 pm

On second thought, a over-rich mixture may have been the cause. This is probably more likely given that the the diesel injection and the gasoline TBI unit operation overlapped during the fuel switch. But, without some basic exhaust makeup/temp data I really couldn't say.

Bummer about the pipe gas incident, Franz. Our County has what the Air Resources Board calls "hot" gas - too little methane, too many impurities (butane, etc), resulting in high energy per unit volume and lower-than-spec octane. This stuff used to kill first-gen CNG engines and the ARB has prohibited it's use in on-road applications.

Modern CNG vehicles like the Honda GX and the GM trucks handle it just fine, but we have to squabble with the ARB and receive waivers to operate vehicles on this fuel to this day!

P.S. Here's a simple comparison of spark ignition, diesel and HCCI operation:

Image
Lenin zhil, Lenin zhiv, Lenin budet zhit'

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