gas injection for td42 diesel

[YNOT]

Although I've never had a car with diesel/gas, or taken a converted car for a drive, as a mechanic (and former automotive LPG fitter) diesel gas makes a lot of sense. By adding a small (about 20 or 30%) of LPG to the diesel combustion process, the burn of fuel inside the cylinder is so much more complete and cleaner.

A typical diesel engine only burns about 75 to 80% of the fuel injected into the cylinder, the rest goes out the exhaust as particulate emissions (or soot), or condenses on the cylinder walls and eventually ends up in the engine oil. Which explains why diesel engine oil goes black.

When you add the small amount of LPG, the diesel burn rate is closer to 97%. The LPG works as an accelerant, causing the diesel to burn more quickly. More fuel being burnt means more power, lower particulate/soot emmissions, and cleaner engine oil. With more of the fuel being burnt in the cylinder, exhaust temperatures often come down too. Fuel economy can improve, but often people just get used to having the extra power for climbing hills etc, so economy remains much the same.

Because you only need 20 to 30% LPG to achieve all this, the gas tank only needs to be about 30% of the size of you diesel tank. If you've got a 145l long range diesel tank, that means you only need a 50l (usable) gas tank. Small tanks are cheaper and much easier to package under the car.

It all just makes sense!


Some other points raised by Peter Kitchener from Redlands 4X4 (Brisbane Bayside)

He does not like putting LPG cylinders under 4WD's, the cylinders are too vunereble to damage. His only exception to this, is when the vehicle is being used for TOURING ONLY.
Unlike petrol LPG conversions where the main fuel tank (between the chassis rails behind the back axle) is usually removed and replaced with an LPG tank, diesel gas conversions usually keep the original fuel tank. So another location needs to be found for the LPG tank.
Peter's prefered location is in the cargo area. He is waiting for a new type of tank to be approved for use in Australia. These new tanks will measure approximately 1m X 1m X 100 to 150mm high, and should fit neatly in the bottom of the cargo area as a false floor.

There are different types of diesel gas systems out there, some expensive, others not so expensive. In short, you get what you pay for. The less expensive systems are not as well controlled, and therefore better suited to constant load engines, gensets etc. The better systems are all processor controlled and much more accurate and tuneable.
The cheaper systems can, under some circumstances, potentially cause engine damage. The majority of diesel gas systems use vapour withdrawal, where the LPG is drawn out of the top of the tank as a vapour. The risk with that is if the liquid LPG in the tank is splashing around (very likely off road), that some liquid could be drawn off into the fuel (service) line. If that liquid were to make it to the engine, it could cause a hydraulic lock in the engine, as liquid does not compress.
The systems Peter fits have an LPG converter to stop this from happening. LPG converters are used to convert liquid LPG to a vapour. His converters do not require connection to the cooling system (with the added complexity that involves), because most of the time the LPG going through the converter is already a vapour.

*Side note; Liquid withdrawal systems require engine coolant running through them all the time to stop them freezing up (due to the latent heat of evaporation as LPG expands from a liquid to a vapour). Diesel gas systems can get away with having vapour withdrawal, as the LPG only makes up about 30% of the engines required fuel supply.

There would be no benefit to fitting diesel gas to a common rail engine, with the LPG technology currently available.The automotive LPG industry lags behind petrol and diesel fuel system technology by a few years. For that reason, Peter does not fit or recommend fitting diesel gas to late model (about 2008 onwards) diesels with common rail fuel systems.

On the other hand, engines like the TD42T benefit greatly from diesel gas. Naturally aspirated engines do not gain as much as their turbo (or super)charged counterparts, as they are not able to supply as much oxygen to the cylinders.

Tony