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Aug 03, 2023

Alternative fuels for transport: The case of LPG in India

As LPG is a relatively cleaner fossil fuel compared to petrol and diesel, promoting its use in the transportation sector will contribute to the reduction of pollution at the local and national level

As LPG is a relatively cleaner fossil fuel compared to petrol and diesel, promoting its use in the transportation sector will contribute to the reduction of pollution at the local and national level

This article is part of the series Comprehensive Energy Monitor: India and the World

In many parts of the world, LPG (liquefied petroleum gas) is also known as “autogas” as it is the most common unblended alternative vehicle fuel in use. The share of autogas in total automotive-fuel consumption ranges from a mere 0.04 percent in the United States to almost 28 percent in Ukraine. Five countries, Russia, Türkiye, Korea, Poland, and Ukraine together accounted for 50 percent of global autogas consumption in 2021 and 25 countries accounted for 80 percent. In India, out of over 348 million registered vehicles, there were just over 2 million petrol-LPG dual-use vehicles registered accounting for about 0.5 percent of total registered vehicles and just over 131,125 LPG vehicles accounting for less than 0.04 percent of total registered vehicles in 2023. Wide differences in the share of LPG use as transportation fuel correspond to differences in government policies.

The amendment of section 52 of the Motor Vehicles Act, 1988 followed by the introduction of LPG Regulation of use in Motor Vehicles Order and the introduction of Central Motor Vehicles (Amendment) Rules in 2001 permitted the use of LPG as an auto fuel. The order issued by the Ministry of Petroleum & Natural Gas (MOPNG) specified that an auto LPG dispensing station (ALDS) dealer would be appointed by a government oil company or a parallel marketeer. The dealer is required to obtain the necessary licence from the Chief Controller of Explosives for meeting safety norms in respect of the dispensing facilities under the Static and Mobile Pressure Vessels (Unfired) Rules, 1981. The order also stated that auto LPG would be sold only by an authorised auto LPG dispensing station dealer. It required that every auto LPG dispensing station dealer would procure or purchase auto LPG either from a government oil company or a parallel marketeer and that no person shall purchase or use auto LPG in a motor vehicle or vehicle unless an auto LPG tank is permanently fitted in the motor vehicle and a conversion kit as approved by the authorities/testing agencies as notified in the Central Motor Vehicles Rules, 2001.

Among other things, the dealer has to take steps to ensure adequate availability of stocks of auto LPG at the dispensing station at all times. The pricing of auto LPG is market-driven outside the administered pricing mechanism but the Government maintains overall control over pricing of non-domestic LPG. As domestic production of LPG is inadequate to cover demand, auto LPG is met from imports. Unauthorised diversion of domestic cylinders for non-domestic use of LPG such as in a motor vehicle is not permitted.

An octane rating is a standard measure of a fuel’s ability to withstand compression and resistance to knock in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonating. Use of fuel with a lower than prescribed octane number may cause the air-fuel mixture to prematurely self-ignite before the ignition system sparks, with a characteristic “knocking” or “pinging” sound, which is undesirable as it may damage engine components due to higher pressures. In a spark-ignition engine, the air-fuel mixture gets heated during the compression cycle and is thereafter triggered by the spark plug to burn rapidly. Higher compression ratios enable the engine to extract more mechanical energy from a given mass of air-fuel mixture, leading to higher thermal efficiency. High compression ratios are typically used with LPG as with petrol, but the octane number of LPG is higher than that of petrol. Widely used petrol brands in India require a minimum 91 octane rating. LPG is a combination of propane and butane and the octane number for propane is 112 and that of butane is 94. The higher-octane number of LPG relative to petrol can offer performance and efficiency advantages.

More advanced ignition timing and a higher compression ratio in LPG engines can be utilised with less susceptibility to pre-ignition or knock compared to standard petrol engines. In spark ignited engines, port fuel injection and direct injection are the most relevant LPG fuelling technologies. With LPG as fuel, port fuel injection systems individual injectors can be controlled to deliver more or less fuel to specific cylinders based on air flow differences among the cylinders. This provides tighter air to fuel ratio control for the engine as a whole, and subsequently more efficient three-way catalytic conversion that reduces the emission of harmful pollutants like HC (hydrocarbon), NOx (nitrous oxide), NH3 (ammonia) and particulate matter (PM).

LPG has an inherent advantage with respect to PM formation compared to petrol in certain engines. The higher volatility of LPG promotes mixing within the combustion chamber providing a less stratified air and fuel mixture reducing locally rich regions that are associated with soot production. The lower carbon intensity of LPG compared to petrol reduces its propensity to produce soot and limits CO2 production. Furthermore, direct injection of LPG in liquid state maintains and can exceed the efficiency advantages of advanced petrol engines.

In India there are dual use LPG vehicles that can switch between petrol and LPG and LPG only models. Dual fuel vehicles require the installation of additional fuel injectors for LPG while LPG only vehicles replace the petrol injectors with LPG injectors. This is necessary due to the lower energy per volume of LPG and lubricity differences that require different injector designs. Regardless of the type LPG vehicles use a dedicated injector per each cylinder and thus offer more refined control of air to fuel ratio on a per cylinder basis compared to single point injection systems.

LPG vehicles work out cheaper than CNG (compressed natural gas) and petrol vehicles. The conversion kit for LPG is less expensive than the conversion kit for CNG and LPG vehicles can cover three times more distance for the same volume of fuel compared to CNG vehicles. The maintenance of LPG vehicles is relatively simpler than CNG vehicles. LPG vehicles and dispensing stations are relatively safer as LPG is stored at 10 – 12 times the atmospheric pressure while CNG is stored at around 200 – 250 times the atmospheric pressure. Using a petrol vehicle with a milleage of 12 km/litre (kilometre/litre) for 50 km a day is likely to cost twice as much as using an LPG vehicle at current prices. Despite these benefits, consumption of LPG for transport is falling in India.

In 2011-12, auto LPG consumption was 233,000 tonnes or just 1.4 percent of total LPG consumption. In 2022-23 auto LPG consumption was just 106,000 tonnes which was less than 0.3 percent of total LPG consumption. Overall LPG consumption grew by over an annual average of 5.3 percent between 2011-12 and 2022-23 while the consumption of auto LPG fell by an annual average of 6 percent. Auto LPG dispensing stations grew from 652 in 2011-12 to 681 in 2014-15. Since then, the number of auto dispensing stations have been falling continuously and stood at 526 in 2022-23. In India, supply side incentives for use of LPG focussed on its use as cooking fuel rather than as transportation fuel. As LPG is a relatively cleaner fossil fuel compared to petrol and diesel, promoting its use in the transportation sector will contribute to reduction of pollution at the local and national level. Reducing the transaction costs in accessing auto-LPG and lightening the regulatory burden in using auto LPG could be among the low-hanging policy initiatives that can boost the use of auto LPG.

The views expressed above belong to the author(s).