Amidst the ongoing heated debate concerning diesel vehicle production in the country, Mehdi Dozandegan, a manager at Adak Polymer Industry, engaged in a comprehensive comparison of diesel and gasoline engines in a conversation with ISNA. He meticulously outlined the advantages and disadvantages of each, shedding light on crucial aspects.
Dozandegan articulated, “Both gasoline and diesel engines operate as internal combustion engines, but the fundamental disparity lies in the fuel injection method, ignition initiation, and the type of fuel used. These factors directly impact the performance and emissions of these engines.”
He further elucidated, “In diesel engines, combustion transpires spontaneously, where a homogeneous mixture of air and fuel enters the combustion chamber and self-ignites at a specific temperature and pressure, instigating combustion. Conversely, in gasoline cars, the fuel is blended with air and introduced into the cylinder, after which a spark plug ignites the mixture to initiate combustion. Notably, in diesel vehicles, the air-to-fuel mixture attains self-ignition, hence the compression ratio in diesel is higher compared to gasoline. Typically, the compression ratio for gasoline engines hovers around 1:8 or 1:12, whereas for diesel, it can range from 1:14 to 1:25. The higher the compression ratio, the more complete the combustion, and it is widely acknowledged that diesel combustion efficiency is approximately 30% higher than gasoline engines.”
The seasoned mechanical expert further delved into the difference in the type of fuel consumed by diesel and gasoline engines, highlighting, “Diesel fuel possesses higher thermal energy in comparison to gasoline. If we burn a gallon of gasoline and a gallon of diesel, the energy derived from diesel will surpass that of gasoline. Another distinctive advantage of diesel engines over gasoline engines is the lower emission of carbon dioxide (CO2).”
Dozandegan underscored that diesel engines exhibit higher torque and power in contrast to gasoline engines. He noted, “This is why diesel engines are preferred wherever high power is requisite, such as in heavy-duty vehicles. Furthermore, gasoline engines have a shorter lifespan, while the maintenance and repair costs for diesel engines are higher.”
He emphasized the price discrepancy between diesel and gasoline engines, explaining, “Diesel engines come at a higher cost compared to gasoline ones, consequently making diesel-powered vehicles relatively more expensive, estimated to be a few hundred dollars more than gasoline vehicles.”
Diesel’s number one issue is its pollution.
Mehdi Dozandegan, a mechanical engineering graduate from Sharif University, highlighted pollution as the paramount challenge associated with diesel engines. He outlined, “The pollution generated by diesel engines presents a significant hurdle. To mitigate this pollution, post-combustion treatment equipment must be installed, significantly driving up the cost of diesel engines compared to gasoline engines. Additionally, maintaining diesel engine pollution within acceptable standards requires regular upkeep of the engine and associated equipment. In a country like Iran, where a car typically remains in use for a decade or two, this poses a significant concern since utilizing post-combustion equipment installed during production for two decades is practically unfeasible.”
Dozandegan stressed that diesel without a post-combustion system is not viable, and the cost of repairing it is exorbitant. He added, “Diesel engines and post-combustion equipment are highly sensitive to fuel quality. If the fuel doesn’t meet the required standards, post-combustion systems rapidly deteriorate, and this degradation is irreversible. Presently, the country does not boast high fuel quality. The fuel quality stands at the Euro 3 standard, with sulfur content in diesel exceeding 350 PPM, whereas it should ideally be around 50 PPM by Euro 4 standards.”
Responding to whether diesel could be a suitable addition to the country’s transportation portfolio, considering both the advantages and disadvantages of diesel engines alongside the domestic conditions, this senior mechanical expert stated, “Given the pollution challenges associated with diesel and the unfavorable fuel scenario in the country, I don’t see a clear rationale for the production of diesel vehicles, as suggested by some automakers. In the current circumstances, the enforcement of the smoke filter law (passed in 2014) has been somewhat compromised due to the substandard quality of diesel. Some automakers and the Ministry of Industry, Mine, and Trade attribute the imperfect implementation of this law to the absence or scarcity of Euro 4 diesel.”
Dozandegan emphasized, “Given the current scenario where the country lacks adequately standardized diesel fuel, introducing diesel vehicles into the country’s transportation system could have disastrous consequences. Furthermore, considering the unfavorable conditions, space limitations, and the prevalent approach to engine and post-combustion equipment maintenance in the country, it’s not an opportune time to introduce diesel passenger vehicles.”
Addressing the state of production and sales of diesel vehicles in Tehran, he noted that the surge in the sale of light diesel vehicles commenced in 1990, driven by reduced fuel consumption and higher efficiency compared to gasoline. However, after the Volkswagen scandal, trust in diesel vehicles dwindled, and subsequently, policies limiting diesel access to specific city areas severely impacted diesel sales.
Dozandegan concluded by emphasizing, “In 2012, the World Health Organization categorized ‘diesel exhaust’ as a Group 1 carcinogen, placing it in the same group as radioactive substances. Consequently, stringent measures have been instituted to combat diesel pollution, employing technologies such as particulate filters and SCR systems (for reducing NOx). While diesel still maintains about 50% of the European market, this share is dwindling, and it is anticipated that hybrid vehicles will soon dominate a significant portion of the diesel share, ultimately phasing out diesel from the market. From my standpoint, this projection seems plausible, particularly concerning diesel passenger vehicles.”
Recently, the Iran Khodro Motor Research Center sought permission from the Department of Environment to commence the production of diesel passenger vehicles. However, this request encountered strong opposition from the organization. Eisa Kalantari, the Deputy President and head of the Department of Environment, firmly stated, “The Department of Environment unequivocally opposes the introduction of diesel engines into the passenger fleet. We sincerely hope that no government grants permission for the incorporation of diesel passenger fleets on the country’s roads and in its cities.”
