LPG dual fuel engines

Сonverted to 100% LPG diesel engine – is it possible? Some time ago it sounded fantastic, now it becomes reality and quite profitable reality.

There is more than 1,1 mln. LPG vehicles owners in Russia, all of them save a lot of expenses using LPG instead of diesel fuel or gasoline. LPG fueling station network consists of more than 2000 station throughout all Russia.


  Join the society of clever vehicle owners and start to save your money! 


How diesel engine can use LPG?

Diesel engine is engine where fuel combustion is performed when heating under the pressure applied. Standard diesel engine couldn’t use LPG fuel, because LPG comparing with diesel fuel has sufficiently higher combustion temperature (diesel fuel 300-330 C, LPG 470 C) which cannot be gained with compression ratio present in standard diesel engine.

Second reason preventing LPG fuel usage in diesel engine is detonation, i.e. improper, burst-like fuel combustion which occurs when excess compression ratio is applied. In diesel engines is used fuel-air mix 14-22 compression ratio when LPG engine should have ratio of 12-14.

That’s why for 100% diesel-LPG conversion two main procedure should be done:

  • Decrease compression ratio

  • Install spark ignition system


After abovementioned procedures accomplishing your diesel engine will use LPG only. Diesel fuel usage recovery is possible after additional works done.

More detailed description of our scope of works you can find in the chapter ‘How actually go about diesel to LPG conversion? ’

How much can I save ?

Your fuel expenses saving value is equal to difference between 100 km diesel fuel expenses before conversion and 100km LPG fuel expenses after.

For example, in MAN TGA case diesel fuel average consumption is 35L/100km, when after 100% LPG conversion LPG average consumption comes out at 46 L. Taking into account 31 roubles (1 USD) diesel fuel price, 100km trip cost is 35USD, and after conversion with 13 roubles (42 cents) per 1L LPG price, 100 km trip cost is 19USD. All prices are based on Russia prices at the end of 2013.

Saving is 16USD or 45% of initial expenses. With 100 000 km annual trip, annual saving is 16 000 USD. Fredliner conversion full expenses (including LPG system parts, LPG tank, installation works, engine processing etc.) was 400 000 roubles (12 900 USD). So as you can see, money back period is 11 months approximately.

LPG additional advantage is easy consumption control: it is virtually impossible to steal and sell LPG because under normal pressure it is in gaseous state.

 You can calculate LPG consumption after conversion basing on the 1,2 -1,4 ratio of LPG to diesel fuel liters of previous consumption (it depends on diesel engine features, its depreciation stage etc)  
Where can I fuel my vehicle with LPG?

There are more than 2500 LPG fueling stations in CIS countries, and more than 2000 station in Russia alone.

You can get up-to-date information regarding LPG fueling stations dislocation and working regime at the interactive map below. Map is kindly supplied by web-site gazmap.ru

When installing LPG tank instead of diesel fuel tank, vehicle full tank mileage is 30% less. But installing of additional LPG tank is not expensive and can be done without any problem. In this case mileage becomes increased up to 30-50%.

What is LPG price forecast?

LPG price is not state-controlled in Russia and is regulated at the free market, according to demand-offer balance. LPG propane can vary according to time of the year because LPG is used for heating in cold season.

Below you can see average LPG and diesel fuel prices in Moscow and Moscow region:


As you can see for 3 years LPG price was changed synchronously with diesel fuel price and saving value was constant almost. Changes come at last 2 years..

LPG price not only stopped to grow but just opposite went down, so saving value grows very fast. What is this: occasion or trend?

 Good news! It is really trend! Which appeared due to state policy towards oil companies: they were compelled to extract and process oil gas dissolved in the extracted oil. Previously it was simply burned at so called “torches” at the oil fields. And 50% of oil gas is actually propane-butane mix, LPG –to-be. So we awaiting great LPG offer at the market which inevitably cause price going down.  

For most interested (and speaking Russian) our visitors: below is biggest Russian LPG producer OSV SIBUR presentation where you can see all details.

How actually go about diesel to LPG conversion?

Diesel engine to LPG conversion needs serious modification of engine parts.

At first we need to change compression ratio (What for? See chapter “How diesel engine can use LPG?” We use various ways to do it, choosing the best one suitable for your engine:

  • Pistons milling
  • Additional cylinder head laying

  • New pistons manufacturing
  • Connection rods shortening


In most cases we use pistons milling (see picture above).

Pistons after milling will be like that:


Than we install system of gas injection through special nozzles and spark ignition system. (What for? See chapter “How diesel engine can use LPG?” ).

We also install few additional sensors and devices (PPS, CAM sensor, oxygen sensor, MAP sensors etc.)

All components are controlled by Engine control unit (ECU).

Conversion kit components:

Общий вид комплектующих для перевода двигателя в газодизелльный режим

Will diesel engine characteristics change after conversion to LPG ?

Power There is common view regarding engine converted to LPG loses up to 25% of power. This is true for dual-fuel gasoline-LPG engines (especially for consumed low-octane fuel gasoline engines with low compression ratio).

For modern turbocharged diesel engines it is not true.

High strength durability of original diesel engine designed for withstanding of 16-22 compression ratio, combined with LPG high octane number, allows us work at 12-14 compression ratio, doing possible to achieve the same and even higher engine power (for you reference: the best sport gasoline engines have compression ratio 11-12)

Typical power –rpm function, with different fuels:


TorqueMax torque value doesn’t change and may becomes increased even. But max torque point shifts to the higher rpm area. It isn’t so pleasant, but according to our experience, drivers don’t complain and get accustomed quickly, especially in the case they got more power capacity.

ReliabilityEngine durability is increased sufficiently. Because LPG combustion grade is higher comparing with diesel fuel even, because compression ratio is less and because LPG don’t contain various impurities like diesel fuel.

Engine oil LPG engines are more demanding to engine oil quality. We recommend to use high-quality all-season oils SAE 15W-40, 10W-40 types and change oil every 10 000 km at least.

If it is possible, better use special oils like Lukoil Efforce 4004 or Shell Mysella LA SAE 40. It is not obligatory, but using those oils brands engine life will be prolonged.

Because of higher water content in gas-air combustion exhaust product, engine oil water-resisting properties are a matter of question, also LPG engines are more sensitive to ash formation in combustion chamber. That’s why sulfate ash-content of engine oil for LPG engines is limited by lower values, while water-resistance demands are higher.

NoiseYou will be amazed! LPG engine is very silent machine comparing with diesel-fueled one. Noise level decreases up to 10-15 dB according to measurement, which means 2-3 times less noise according to subjective feeling.

Nobody cares about emissions here in Russia. But may be… ?

LPG engine ecological parameters sufficiently exceed its diesel analog and give way to electric and hydrogen engines only.

It can be clear visible when comparing exhaust smoking, the most important factor at big cities. Smoke tale of diesel buses is the biggest annoying feature of public transportation in cities. LPG engines are free of this disadvantage because there is no ash when LPG combustion.

The only one LPG disadvantage comparing with diesel fuel is higher CO emission (up to 5%), but CO can be easy neutralized by standard 3-stage neutralizer, and it goes to exhaust as harmless CO2


Prices and time periods.

Price and time period necessary for LPG conversion are defined individually taking into account engine type, vehicle type, order volume etc. For preliminary calculation you can use following table:

Parameter Light truck, mini-bus Dump-truck, medium-duty truck, medium bus Heavy duty truck, big bus
Cylinders 4 4-6 6-8
Engine power, h.p. 50-150 150-250 250-700
Conversion time (certification time not included), days 5-10 7-12 10-15
LPG tank, L >40 >60 >100
LPG system (underhood equipment only) cost, USD >6000 >7000 >8000
LPG storage system cost, USD >200 >500 >1000
Total conversion cost, USD >6700 >7700 >9500