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Description of technology

Conversion of the Nissan diesel engine, as fitted by London Taxi International, in the Fairway and TXI taxis, to dedicated LPG fuelling.

From the outset Jaymic’s concept of the technology to convert black cabs to a cleaner fuel has been to be ecologically sound as well as saving valuable energy resources. In using as much of the existing Nissan engine and ancillaries as possible this economy of resources can be achieved. Rather than removing a mechanically sound diesel engine scrapping it and replacing it with a brand new engine that, in itself, has used a significant amount of energy to manufacture, our technology allows the ongoing use of the most basic components of the original engine and ancillaries and forms the basis of our ecological conversion concept that has been followed throughout our research, development work, prototype and production stages.

Our technology recycles the existing Nissan TD27 diesel engine in the LTI taxis, as installed by LTI between January 1989 and January 2002, converting the engine from a compression ignition diesel to a spark ignition engine with dedicated LPG fuelling. The only original parts of the LTI taxi that are scrapped are the diesel tank, exhaust down pipe and diesel fuel system.

By having dedicated LPG as the fuel we can take advantage of the higher octane rating of LPG, compared to petrol, by optimising the compression ratio and ignition timing to run more efficiently. An engine that runs on either petrol or LPG has to be optimised for the lowest quality fuel, which is petrol.

Both the higher compression ratio and optimised ignition map increase the efficiency of our dedicated LPG engine and give large reductions in NOx and PM emissions.

Engine conversion procedure

Fairway and TXI - the original Nissan TD27 diesel engine is removed and stripped to component form and inspected for wear. Depending on the tolerances found, the cylinder liners and pistons are replaced, or the pistons only replaced. The rest of the bottom half of the engine is rebuilt using new bearings, oil pump, seals, gaskets, etc.

A Jaymic-designed and modified cylinder head is installed on the engine. The old diesel cylinder head being remanufactured to be used with LPG, including suitable valves and seats for gaseous fuels.

The original air filter housing, inlet and exhaust manifolds are used in the conversion.

The end result is not only a taxi that is converted to run on LPG, but with a fully reconditioned engine without having to replace the existing engine.

LPG fuelling and ignition system

In the boot of the Fairway model taxi is a 110 litre LPG tank on a purpose made mounting frame. TXI models have a 105 litre tank The LPG tank frame has provisions for mounting the vehicle jack, wheel chair ramps and passenger step. The LPG filler is mounted in the original position of the diesel filling point. The original fuel gauge in the vehicle monitors the level of the LPG in the fuel tank.

The LPG fuel system on both the Fairway and TXI models is a single point gaseous phase induction system producing emissions control performance between Euro III and Euro IV levels on the Fairway and TXI taxis. An ignition/fuel management system is combined in the same ECU.

Exhaust system

The taxi is fitted with a new exhaust down-pipe that includes, oxygen sensor and catalytic converter.


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