Use Of Compressed Natural Gas Research Articles

An assessment of methane emission from the CNG cylinder testing stations in Delhi and its implication for global warming.

Methane is an important greenhouse gas, which constitutes minimum 90% of automotive grade compressed natural gas (CNG) used in India. The use of CNG as automotive fuel has been implemented in almost all major tier I to tier III cities of the country. Delhi, the capital city of India, has world largest CNG-fuelled public transport system. The cylinders fitted to the CNG-fuelled vehicles are required to be subjected to hydrostatic stretch test every 3years at Government of India approved CNG cylinder testing stations, as mandated under Rule 35 of Gas Cylinders Rules, 2016. During the testing of cylinders, CNG present in the cylinders are discharged in the atmosphere at the degassing point of CNG testing stations. This study estimates annual methane emissions from the CNG cylinder testing stations of Delhi. The annual average methane emission from the CNG cylinder testing stations of Delhi was found to be 30.8 tons during the year 2019. The uncertainties in the emission estimate are also identified and discussed.

Pulmonary function tests in compressed natural gas pump workers in Surat city

Background: Various studies have known abatements in lung function and several other health problems associated with longstanding air pollution exposure. One of the most cost-effective and environmental alternative of conventional fuels (petrol and diesel) is compressed natural gas (CNG). The increasing use of CNG as a fuel (as it is safe and cheap as compare to the conventional fuels) can add one more bug to the list of work-related disease. Aims and Objectives: This study is to evaluate the respiratory functions of CNG pump workers. Materials and Methods: The present study was held on 82 male subjects. The study group included of non-smoking healthy adult males, age group of 20–40 years working in different CNG stations in Surat city for >6 months and 8 h per day. The control group included of non-smoking healthy adult males, age group of 20–30 years working or studying in the Surat Municipal Institute of Medical Education and Research (SMIMER). Results: Out of 82 male subjects, 30 subjects were control and 52 subjects were CNG station workers. The study group comprised of 52 healthy non-smokers in the age group of 20–40 years working in different CNG station in Surat city for >6 months and 8 h/day. The control group comprised of 30 healthy non-smokers males between the age group of 20–30 years working or studying in the SMIMER. Conclusion: In this study, we have not found statistically significant deterioration in pulmonary functions of CNG pump workers when compared to controls.

Influence of Injection Pressure on the Dual-Fuel Mode in CI Engines Fueled with Blends of Ethanol and Tamanu Biodiesel

The acceleration of global warming is primarily attributable to nonrenewable energy sources such as conventional fossil fuels. The primary source of energy for the automobile sector is petroleum products. Petroleum fuel is depleting daily, and its use produces a significant amount of greenhouse emissions. Biofuels would be a viable alternative to petroleum fuels, but a redesign of the engine would be required for complete substitution. The use of CNG in SI engines is not new, but it has not yet been implemented in CI engines. This is due to the fuel having a greater octane rating. The sole use of CNG in a CI engine results in knocking and excessive vibration. This study utilizes CNG under dual-fuel conditions when delivered through the intake manifold. In a dual-fuel mode, compressed natural gas (CNG) is utilized as the secondary fuel and a blend of 90% tamanu methyl ester and 10% ethanol (TMEE10) is used as the primary fuel. The injection pressure (IP) of the primary fuel changes between 200 and 240 bar, while the CNG induction rate is kept constant at 0.17 kg/h. The main combustion process is governed by the injection pressure of the pilot fuel. It could be affecting factors such as the vaporization characteristics of the fuel, the homogeneity of the mixture, and the ignition delay. Originally, tamanu methyl ester (TME) and diesel were used as base fuels in the investigation. As a result of its inherent oxygen content, TME emits more NOx than diesel. The addition of 10% ethanol to TME (TMEE10) marginally reduces NOx emissions in a CI mode because of its high latent heat of vaporization characteristics. Under peak load conditions, NOx emissions of TMEE10 are 6.2% lower than those of neat TME in the CI mode. Furthermore, the experiment was conducted using TMEE10 as the primary fuel and CNG as the secondary fuel. In the dual-fuel mode, the TMEE10 blend showed higher combustion, resulting in an increase in performance and a significant decrease in emission characteristics. As a result of the CNG’s high-energy value and rapid burning rate, the brake thermal efficiency (BTE) of TMEE10 improves to 29.09% compared to 27.09% for neat TME. In the dual-fuel mode of TMEE10 with 20.2% CNG energy sharing, the greatest reduction in fuel consumption was 2.9%. TMEE10 with CNG induction emits 7.8%, 12.5%, and 15.5% less HC, CO, and smoke, respectively, than TME operation.

Modelling Fuel Cut Off Controller on CNG Engines Using Fuzzy Logic: A Prototype

Compressed Natural Gas (CNG) is an alternative solution to the limited availability of fossil energy. CNG use's advantages include high octane value, applicable to vehicles requiring large power, cost-effectiveness, and lower emissions. However, applying the old CNG kit leaves emission problems and fuel wastage during deceleration. Although numerous studies have been carried out with numerous variables to improve engine performance and emissions, reports regarding deceleration interventions are still limited. Therefore, this study proposes enhanced modeling to optimize the fuel cut-off controller by applying fuzzy logic by controlling the throttle valve position based on the input sensor of the engine. Engine dynamics, fuel characteristics, and intake systems are considered strictly in the development of the control system to obtain more precise results that refer to the complete combustion process. The designed model has advantages over previous studies, which focused on achieving CNG AFR stoichiometry to improve fuel economy by using the fuel cut-off method during deceleration. The results showed that fuel savings could be increased during deceleration by cutting off fuel flow to the engine. This can be seen from the increase in AFR ± 57% and decrease ± 38% - 67% in CNG flow rate during deceleration which is promising to be widely applied. In the future, the proposed model could be used as part of the vehicle component in optimizing the fuel consumption that will support green technology sustainability.

Fuel flexibility study of various fuels with charge dilution and high compression ratio for medium-load operating RCCI engine

This study examines the dual-fuel (RCCI) combustion mode using gasoline, ethanol, methanol, and compressed natural gas (CNG) as low reactive fuels (LRF) and diesel, neem biodiesel as high reactive fuel (HRF). The fresh and diluted charge (with hot EGR) combustion is compared at a high compression ratio for medium load operation. For obtaining the near-zero NOx-soot emissions and improved performance, the feasibility of different reactivity and renewable fuels are studied. The use of methanol and gasoline as LRF and diesel as HRF with charge dilution shows improved fuel-air-mixing, reactivity stratification, and thermal efficiency. The use of ethanol and gasoline as LRF and biodiesel as HRF with charge dilution shows near-zero NOx emissions while soot emissions are above the minimum acceptable range. The use of CNG as LRF and diesel as HRF with charge dilution shows minimum thermal efficiency and high fuel consumption. The reduced combustion rate and increased premixed combustion with charge dilution result in lower combustion temperatures and pressure rise rates for G + D and M + D.

Uji Performa Mesin Bensin dengan Sistem Injeksi Berbahan Bakar HCNG

Compressed Natural Gas (CNG) is an alternative renewable fuel gasoline replacement. However, due to the low heating value, the use of CNG in the engine will reduce its performance. The addition of hydrogen gas in CNG namely hydrogen-enriched compressed natural gas is expected to increase the power of the motor. This study aims to analyze the effect of hydrogen concentration on the performance of a CNG gasoline engine. The research was conducted on the engine with an indirect fuel injection system with a volume of 124,9 cc. The parameter of the engine that measured is torque, effective power, specific fuel consumption, and effective thermal efficiency. The results showed that the small percentage of hydrogen in CNG could increase the power of the gasoline engine. Power and efficiency reach a maximum of 10% hydrogen concentration. Increasing the proportion of hydrogen in CNG fuel above 10% will significantly reduce engine torque and power. Engine performance at optimal conditions with 10% hydrogen results in torque of 2.71 Kg.m at 670 rpm, effective power of 3.28 Ps at 1055 rpm, SFCe 0.17 Kg / Ps. Hours at 770 rpm and 33.62% effective thermal efficiency at 770 rpm

Impact of Compressed Natural Gas (CNG) Fuel Systems in Small Engine Wood Chippers on Exhaust Emissions and Fuel Consumption

The projected increase in the availability of gaseous fuels by growing popularity of household natural gas (NG) filling stations and the increase in the production of gaseous biogas-derived fuels is conducive to an increase in the use of NG fuel. Currently, natural gas in various forms (compressed natural gas (CNG), liquefied natural gas (LNG)) is popular in maritime, rail and road transport. A new direction of natural gas application may be non-road mobile machines powered by a small spark-ignition engine (SI). The use of these engines in the wood chippers can cause the reduction of machine costs and emissions of harmful exhaust gases. In addition, plant material chippers intended for composting in bio-gas plants can be driven by the gas they are used to produce. The biogas can be purified to bio-methane to meet natural gas quality standards. The article presents the design of the natural gas supply system, which is an upgrade of the Lifan GX 390 combustion engine spark ignition engine (Four-stroke, OHV (over head valve) with a maximum power of 9.56 kW), which is a common representative of small gasoline engines. The engine is mounted in a cylindrical chipper designed for shredding branches with a maximum diameter of up to 100 mm, which is a typical machine used for cleaning work in urban areas. The engine powered by CNG and traditionally gasoline has been tested in real working conditions, when shredding cherry plum (Prunus cerasifera Ehrh. Beitr. Naturk. 4:17. 1789 (Gartenkalender4:189–204. 1784)). Their diameter was ca. 80 mm, 3-metere-long, and humidity content ca. 25%. The systems were tested under the same actual operating conditions, the average power generated by the drives during shredding is about 0.69 kW. Based on the recorded results, it was found that the CNG-fuelled engine was characterized by nitrogen oxides (NOx) emissions higher by 45%. The other effects of CNG were a reduction in carbon dioxide (CO2), carbon monoxide (CO) and hydrocarbon (HC) emissions of about 81%, 26% and 57%, respectively. Additionally, the use of CNG reduced fuel consumption by 31% and hourly estimated machine operating costs resulting from fuel costs by 53% (for average fuel price in Poland: gasoline: 0.99 EUR/L and CNG: 0.71 EUR/m3 on 08 November 2020). The modernization performed by the authors ensured the work of the drive unit during shredding, closer to the value of stoichiometric mixtures. The average (AVG) value of the air fuel ratio (AFR) for CNG was enriched by 1.2% (AVG AFR was 17), while for the gasoline engine the mixture was more enriched by 4.8% (AVG AFR was 14). The operation of spark-ignition (SI) combustion engines is most advantageous when burning stoichiometric mixtures due to the cooperation with exhaust aftertreatment systems (e.g., three-function catalytic converter). A system powered by CNG may be beneficial in systems adapting to operating conditions, used in low-power shredding machines, whose problem is increased HC emissions, and CNG combustion may reduce them. The developed system does not exceed the emission standards applicable in the European Union. For CO emissions expressed in g/kWh, it was about 95% lower than the permissible value, and HC + NOx emissions were 85% lower. This suggests that the use of the fuel in question may contribute to tightening up the permissible emission regulations for non-road machinery.

Experimental investigations of an automotive diesel engine fuelled with natural gas in dual fuel mode

The compressed natural gas (CNG) is a viable alternative fuel for diesel engine use due to its good combustion properties and low carbon content. The general objective of the research is CNG use at the automotive diesel engine for improving of the energetic performance and decrease of the emissions level. By achieving these specific objectives, the paper brings an important contribution to solving pollution problems in large urban areas for diesel engines, the solution can be easily implemented on diesel engines in running, even on the old design which can be converted to fit the current rules of pollution. All investigations were conducted at engine operating regime of 55% load and 2000 rev/min. Following the analysis of all recorded data the proper quantity of CNG will be determined in order to have lower emissions level and better energetic performances. The specific energetic consumption is expected to decrease with more than 40%; at the highest substitution ratio the maximum in-cylinder pressure reaches values superior with more than 10% and the maximum pressure rise rate with over 20%; CO2 emission reaches 10% lower level. The CNG use at automotive diesel engine leads to the improvement of combustion process and engine energetic performance.

Development of tractor gas-diesel modifications

A system for reducing toxicity has been developed that includes the use of compressed natural gas (CNG) and exhaust gas recirculation (EGR) and is intended for both new tractors and those in service. The use of CNG does not require expensive equipment, significant design changes, and re-equipment is possible in specialized workshops of farms and repair and technical enterprises.

Use of CNG as Autofuel in Nigeria

Natural gas is a clean-burning, safe fuel that can save you money at the pump while benefitting the environment and reducing Nigeria’s dependence on petroleum. It is a naturally occurring mixture of gaseous hydrocarbon, non-gaseous non-hydrocarbons and gaseous non-hydrocarbons found in underground reservoir rocks either on its own (non-associated gas) or in association with crude oil (associated gas). Natural gas is today accepted as one of the best sources of energy for the world and for the future because of its environmentally-friendly nature compared to other kinds of fossil fuels. Nigeria is ranked as the seventh most natural gas endowed nation in the world and relaxes on number one spot in Africa as she seats on about one hundred and eighty-eight trillion cubic feet of natural gas deposits.Current opportunities to utilize gas in Nigeria include: Gas to reinjection schemes, Gas to power schemes, Gas to petrochemicals (as feedstock), LNG-Liquefied Natural Gas, LPG- Liquefied Petroleum Gas, and CNG- Compressed Natural Gas. The use of CNG as auto fuel in Nigeria presents so much benefits as have been highlighted in this paper with emphasis on the economic advantage. Compressed Natural Gas (CNG) is a product of compressing natural gas to one hundredth the volume it occupies at standard atmospheric pressure.A comprehensive economic analysis to determine the cost savings from driving a car on CNG against PMS considered the case of a motorist who covers an average of 100 km every day in the approximately thirty days that make a month was employed. Results established that running a car on CNG amounts to saving N1 143 daily and N34 284 monthly, the cost of converting the car from PMS - driven to CNG - driven is recovered before the end of the sixth month. From the sixth month to the end of the first year, savings of N211 402 is made. Savings of N411 408 is enjoyed each year after the first year.Running vehicles on CNG will greatly reduce the friction and troubles encountered in importing fuel into the country. This will also cut down largely the hardly available foreign exchange expended in bringing in PMS for fuelling vehicles. To this end, the Nigerian Government should as a matter of national development ensure legal and regulatory framework encompassing both technical and commercial aspects for natural gas utilization in Nigeria. Worthy of note is the aspect of gas gathering, gas transmission and distribution which will further encourage the planting of CNG refuelling stations that will serve the expected large fleet of natural gas vehicles. Currently, Green Gas Limited, a joint venture between Nigeria Gas Company (NGC) a Nigerian National Petroleum Corporation (NNPC) and NIPCO Plc. that has nine operational CNG refuelling stations and others under construction is the only company driving the CNG revolution in the country.

Use of CNG as Autofuel in Nigeria

Natural gas is a clean-burning, safe fuel that can save you money at the pump while benefitting the environment and reducing Nigeria’s dependence on petroleum. It is a naturally occurring mixture of gaseous hydrocarbon, non-gaseous non-hydrocarbons and gaseous non-hydrocarbons found in underground reservoir rocks either on its own (non-associated gas) or in association with crude oil (associated gas). Natural gas is today accepted as one of the best sources of energy for the world and for the future because of its environmentally-friendly nature compared to other kinds of fossil fuels. Nigeria is ranked as the seventh most natural gas endowed nation in the world and relaxes on number one spot in Africa as she seats on about one hundred and eighty-eight trillion cubic feet of natural gas deposits.Current opportunities to utilize gas in Nigeria include: Gas to reinjection schemes, Gas to power schemes, Gas to petrochemicals (as feedstock), LNG-Liquefied Natural Gas, LPG- Liquefied Petroleum Gas, and CNG- Compressed Natural Gas. The use of CNG as auto fuel in Nigeria presents so much benefits as have been highlighted in this paper with emphasis on the economic advantage. Compressed Natural Gas (CNG) is a product of compressing natural gas to one hundredth the volume it occupies at standard atmospheric pressure.A comprehensive economic analysis to determine the cost savings from driving a car on CNG against PMS considered the case of a motorist who covers an average of 100 km every day in the approximately thirty days that make a month was employed. Results established that running a car on CNG amounts to saving N1 143 daily and N34 284 monthly, the cost of converting the car from PMS - driven to CNG - driven is recovered before the end of the sixth month. From the sixth month to the end of the first year, savings of N211 402 is made. Savings of N411 408 is enjoyed each year after the first year.Running vehicles on CNG will greatly reduce the friction and troubles encountered in importing fuel into the country. This will also cut down largely the hardly available foreign exchange expended in bringing in PMS for fuelling vehicles. To this end, the Nigerian Government should as a matter of national development ensure legal and regulatory framework encompassing both technical and commercial aspects for natural gas utilization in Nigeria. Worthy of note is the aspect of gas gathering, gas transmission and distribution which will further encourage the planting of CNG refuelling stations that will serve the expected large fleet of natural gas vehicles. Currently, Green Gas Limited, a joint venture between Nigeria Gas Company (NGC) a Nigerian National Petroleum Corporation (NNPC) and NIPCO Plc. that has nine operational CNG refuelling stations and others under construction is the only company driving the CNG revolution in the country.

Performance and emission characteristics of a CNG-Biodiesel dual fuel operation of a single cylinder four stroke CI engine

The introducement of stringent emissions norms like Euro V and Euro VI is diverting the research to develop new technologies to reduce the engines exhaust emissions. Many researchers have adopted different techniques for lowering the tailpipe emissions from the engines where oxides of nitrogen (NOx) and smoke are mainly formed. In this study a diesel engine having single cylinder is converted into dual-fuel engine to operate with pilot injection of Diesel/biodiesel ethanol blend and Compressed natural gas (CNG). The engine was operated on both single fuel(SF) and dual fuel(DF) mode. The CNG was inducted into the inlet manifold through a gas carburettor on purpose designed for this application. The injection timings was optimized for CNG- biodiesel. The optimum injection timing was 27°BTDC. The pilot fuel injection pressure was maintained at 230 bar. Engine was operated with optimum Compression ratio of 17.5 and CNG flow rate was optimized and found to be 0.5 kg/h. The effect of CNG induction on combustion and emissions characteristics of a compression ignition engine with a dual fuel was studied and compared with single fuel operation. Comparative results revealing the effect of dual fuel combustion on the engine performance, combustion and exhaust emissions. Based on the performance, combustion and emission characteristics it is concluded that, use of CNG in the dual fuel mode in a diesel engine improves the performance and reduces the exhaust emissions from the engine except for HC and NOX emissions.

Comparative Study between Early and Late Injection in a Natural-gas Fuelled Spark-ignited Direct-injection Engine

Natural gas is a cleaner burning alternative fuel that has the potential to widely replace conventional fuels. The use of Compressed Natural-Gas (CNG) in spark-ignited (SI) engines can reduce CO2 emissions by up to 20% compared with gasoline operation. Currently, all spark-ignited CNG engines for passenger vehicles are port-fuel injected (PFI). They suffer loss of peak torque and power due to a reduction in volumetric efficiency. Direct-Injection can overcome this drawback by injecting the fuel after intake valve closure, leading to significant improvements in torque output. In this experimental study, we present the effects of injection timing, before and after the inlet valve closure on combustion duration and engine thermal efficiency at low load and WOT (Wide Open Throttle) conditions. At low-loads, late-injection increases pumping losses compared to early-injection at a given loading condition but combustion is faster due to higher turbulence at the time of ignition. As a result, the thermal efficiencies are similar at these injection timings.

The Potential Reduction of Carbon Dioxide (CO2) Emissions from Gas Flaring in Nigeria’s Oil and Gas Industry through Alternative Productive Use

Globally, climate change and its adverse effects on the human population and the environment has necessitated significant research on the sustainable use of natural resources. Gas flaring in Nigeria’s oil and gas industry causes environmental and health hazards and to a large extent, culminates in yearly loss of the Nation’s revenue. The aim of the study is to highlight the potentials of converting flared gas from the Nigerian oil and gas industry to compressed natural gas (CNG) which could be an alternative fuel for the 220 Lagos Bus Rapid Transit (BRT-Lite) while reducing CO2 emissions. In addition, the study provided an overview of gas flaring in the oil and gas industry and energy utilisation in some selected sectors in the country. The Long-range Energy Alternative Planning System (LEAP) software was employed to model the energy demand and carbon dioxide emissions from the BRT-Lite by creating a current scenario and projections to the year 2030. The use of CNG as an alternative fuel for Lagos BRT-Lite will significantly reduce CO2 emissions in Nigeria’s oil and gas industry. Other utilization options for flared gas from this industry includes: Liquefied Natural Gas (LNG), Liquefied Petroleum Gas (LPG), and power generation.

A stakeholder analysis of the automotive industry's use of compressed natural gas in Nigeria

Nigeria experiences a perennial shortage of transportation energy despite being the world’s eighth largest producer of crude oil and the seventh largest proven reservoir of natural gas. Partly as a result, the Nigerian government proposed the use of compressed natural gas (CNG) as an automotive fuel in 1997 as part of the efforts to harness the country’s natural gas resources and address transportation energy challenges. However, the rate of adoption has been very low with natural gas vehicles constituting 0.04% of the national vehicle fleet. This paper presents a stakeholder analysis derived from interviews with senior executives of the leading organisations involved in the energy and transportation sectors in Nigeria. Analysis revealed thirty-one barriers and twenty-six policy proposals that were categorised into eight and four themes respectively. While there is a rarity of agreement across all stakeholder groups, we observed consensus on the suggestion for the removal of the subsidy on petrol and the need for the establishment of a coordinating agency to drive the use of CNG. The paper offers specific recommendations for the reform of the energy and transportation sectors, the introduction of fiscal and operational incentives and the creation of public awareness.

When Courts Plan: The Greening of Delhi's Autorickshaws

Implementing municipal-scale policies is challenging in megacities. Despite this, between 1986 and 2006, Delhi converted its entire public transportation network of nearly 100,000 vehicles to use Compressed Natural Gas (CNG) instead of diesel and petrol. The use of CNG is widely assumed to have been ordered by the Supreme Court of India. But this overlooks how autorickshaws, privately owned and making up three-fourths of these vehicles, came to use CNG even though the court did not order it. Using two new sources of data, I show that the conversion of autos was jointly led by the largest private manufacturer together with the city government. The court facilitated coordination between several other actors, allowed them to experiment, and monitored progress over two decades leading up to the auto conversion. After capping the total number of autos, it ultimately refrained from passing judgment on two consequential aspects of greening them: vehicle ownership and fuel type. As a result, auto owners were buffeted by decades of incremental policy experimentation. Eventually, these experiments reconfigured auto ownership as some sold their operating permits to become renters, while state institutions remained indifferent to this shadow conversion underfoot.

Compressed natural gas as a feasible replacement fuel for U.S. transportation

There has been much attention for many years on reducing U.S. fuel imports in order to improve energy independence. The transportation sector is one of the most important components with its share of 28% of total U.S. energy consumption. In this research, compressed natural gas (CNG) is examined as an alternative fuel for the U.S. transportation sector. To be able to answer this question it is essential to understand both the supply and demand sides of the problem. This research aims to exhibit the availability and adequacy of CNG as a full or partial fuel replacement for U.S. transportation sector needs, the factors that prevent CNG from being a widely used transportation fuel, the cost–benefit of using CNG as a vehicle fuel, and feasible changes to make CNG more cost effective. In conjunction with putting forth this information for consideration, the best short- and long-term scenarios for CNG use in the transportation sector, provided through the application of analytic hierarchy process (AHP), is proposed.

The analysis of the potential for the use of gaseous fuels in the municipal bus transit in Poland – part 2

The paper discusses issues related to the use of compressed natural gas (CNG) in combustion engines particularly in municipal bus transport. The ecological aspects of the use of natural gas in road transport have been analyzed particularly the exhaust emissions in comparison to the emissions from diesel engines. Advantages and disadvantages of natural gas fueling as well as the current level of CNG use in transport have been presented both in Poland and worldwide. The authors have also indicated the motivating arguments for the use of natural gas.

The analysis of the potential for the use of gaseous fuels in the municipal bus transport in Poland – part 1

The paper discusses issues related to the use of compressed natural gas (CNG) in combustion engines particularly in municipal bus transport. The ecological aspects of the use of natural gas in road transport have been analyzed particularly the exhaust emissions in comparison to the emissions from diesel engines. Advantages and disadvantages of natural gas fueling as well as the current level of CNG use in transport have been presented both in Poland and worldwide. The authors have also indicated the motivating arguments for the use of natural gas.

Inherent Fuel Consumption and Exhaust Emission of the CNG–Petrol Bi–Fuel Engine Based at Non–Loaded Operation

Gas asli termampat (CNG) merupakan bahan api alternatif yang paling berjaya dan digunakan dengan meluas bagi kenderaan terkini yang berada di pasaran. Kenderaan pacuan petrol bagi tujuan ini biasanya dilengkapkan dengan kit penukar gas asli bagi membolehkan operasian dwi-bahan api di antara CNG dan petrol. Pendekatan secara uji kaji ini difokuskan ke atas penggunaan bahan api, emisi ekzos dan kos bahan api di antara operasian gas asli dan petrol. Rig ujian terdiri dari sebuah sistem enjin teksi dwi-bahan api menggunakan 1500 cc dengan 12 injap sistem karburetor adalah dibina khusus. Penggunaan bahan api dan emisi ekzos yang setara diperolehi pada kelajuan putaran seminit (rpm) enjin yang berbeza ketika operasian menggunakan bahan api CNG dan petrol secara berasingan. Pengoperasian rpm enjin tanpa bebanan diubahsuai dari kedudukan pegun kepada kedudukan melebihi 5000 rpm untuk memperolehi profil penggunaan bahan api dan emisi ekzos. Kedua-dua data yang diperolehi ini kemudiannya digunakan bagi mengira kadar udara bahan api enjin. Kesemua ketiga-tiga parameter yang diperolehi digunakan untuk membuat perbandingan terhadap operasian gas asli dan petrol. Pemerhatian yang dibuat menunjukkan kadar udara bahan api bermula dari 19 ke 16.3 bagi operasian petrol dan dari 40 ke 18.7 untuk operasian menggunakan gas asli. Emisi ketika operasian menggunakan CNG jelas menunjukkan penurunan ketara ke atas keluaran hidrokarbon (HC), karbon monoksida (CO), karbon dioksida (CO2) dan nitrogen oksida (NOx) dibandingkan dengan operasian menggunakan petrol. Dari segi kos, penggunaan CNG memberikan keuntungan melebihi 50% terhadap kesemua kelajuan rpm enjin jika dibandingkan dengan operasian menggunakan petrol. Kata kunci: NGV, enjin dwi–bahan api, pengunaan bahan api, emisi ekzos, CNG, gas asli Compressed natural gas (CNG) is the most successful and widely used alternative fuel for vehicles in the market today. Petrol fuelled vehicles are fitted with natural gas vehicle (NGV) conversion kit to enable bi-fuel operation between CNG and petrol. This experimental approach is focused on the fuel consumption, exhaust emission and fuel cost between natural gas and petrol operations. The specially constructed test rig comprises of the bi-fuel fuel system employed in the 1500 cc 12 valves carburettor engine NGV taxis. The inherent fuel consumption and corresponding exhaust emission are acquired at different engine revolution per minute (rpm) during petrol and CNG operation separately. The engine rpm operating without load is varied from idle to more than 5000 rpm to acquire the fuel consumption and exhaust emission profile. These two acquired data are then used to calculate the engine’s air fuel ratio. All three parameters acquired are used to conduct comparisons between petrol and natural gas operation. It is seen that the bi-fuel system operates with air fuel ratio ranging from 19 to 16.3 for petrol operation and ranges from 40 to 18.7 for natural gas operations. The emission during CNG operation clearly shows significant decrease in hydrocarbon (HC), carbon monoxide (CO), carbon dioxide (CO2) and nitrogen oxide (NOx) over the use of petrol. In terms of cost, the use of CNG provides savings exceeding 50% through all engine rpm compared to petrol non-loaded operations. Key words: NGV, bi–fuel engine, fuel consumption, exhaust emission, CNG, natural gas