When the issue is the use of petroleum derivatives in combustion engines, the competitive advantages of ignition by compression engines (Diesel engines) over spark-ignited engines (Otto engines) are well known. They are mainly due to the higher energy efficiency of diesel engines in comparison to the lower production cost gasoline engines in a same power range, given that the cost of a unit of energy of the two fuels is about the same.

The global trend has been a slight increase in the share of diesel engines. Although a diesel engine emits a smaller quantity of pollutants per net work unit, post-combustion gas treatment systems render spark-ignited engine applications less polluting. Most of the pollution of large urban centers is due to nitrogen oxide emissions and particulate material from diesel engines.

In contrast, the emission of greenhouse gases per net work unit is lower in diesel engines than in gasoline engines, given the former’s higher energy efficiency. On the other hand, because of ethanol’s volatility and high resistance to self-inflammation, it is an ideal fuel for spark-ignited engines, just as vegetable oils and derivatives, such as biodiesel, are better suited for ignition by compression engines.

One should, however, observe that, when Otto cycle engines are optimized for ethanol, their energy yield is better than when optimized for gasoline. In the case of diesel cycle engines, however, the energy yield varies little when optimized for different fuels, albeit the difficulties in engine adaptation may vary greatly between fuels. In the case of ethanol, unlike biodiesel, the changes needed are big.

Therefore, in a fuel for engines market that is reasonably balanced and dominated by fuel from petroleum, it makes sense to use ethanol rather than gasoline and to extract more diesel oil. In addition, in most countries, taxes on gasoline are higher than on diesel oil, so one may conclude that there is no room for ethanol in applications dominated by diesel oil.

However, there still is no global market for ethanol and local markets are far from balanced, creating opportunities for the use of ethanol instead of diesel oil. In Brazil, the price relation between ethanol, gasoline and diesel oil cannot be ignored. From the energy point of view, 1.72 liters of hydrated ethanol or 1.22 liters of gasoline C are necessary to replace 1 liter of diesel oil.
 

Thus, admitting that the price of diesel is within a range of 85% to 90% of the price of gasoline C, every time the ethanol price drops below the gasoline price floor of 49% to 52%, there is economic potential for consumers to use ethanol. One should mention that the price relation between hydrated ethanol and gasoline C, that makes the former feasible, is 70%.

When considering the sale price of hydrated ethanol (w/o taxes) and the purchase price of diesel oil, the opportunity for replacement becomes economically advantageous when the price ratio falls below 77% to 81%. Even when one considers ethanol being used in spark-ignited engines, these limits are at about 68%. This shows that replacing diesel with ethanol has economic potential that is even higher when replacing gasoline C by hydrated ethanol in flex-fuel vehicles.

Given this reality, the need to develop technical alter-natives for use of ethanol as replacement of diesel becomes apparent. In June 2009, average fuel prices per unit of energy in São Paulo were: hydrated ethanol - R$44/GJ; diesel oil - R$52/GJ; and biodiesel - R$70/GJ. The large incentive provided biodiesel illustrates the importance of finding a renewable replacement for diesel oil.

Two typical applications in diesel engines are promising for the use of ethanol:
1. buses for urban passenger transportation, and
2. agricultural machinery and cargo vehicles.

The former has the advantage that its use is limited to private fleets, with the additional benefit of potentially qualifying for fiscal incentives. The second application’s feasibility lies in the cost of the fuel and, hence, in developing optimized technical solutions for ethanol. Three presentations on this subject were made in the panel “Ethanol: New Options for Diesel Engines”.

J. Moreira, President of the Board of CENBIO – National Reference Center on Biomass – and coordinator of project BEST – Bioethanol for Sustainable Transportation, presented the development of the demo project of the urban bus powered by additivated hydrated ethanol. It runs on a Scania diesel engine, with a compression rate of 28:1 and a special Bosch injection system for ethanol.

The technology was modified to use an ethylene glycol based additive. This technology has been applied in buses in Stockholm. The reduced emission of pollutants has allowed keeping this bus fleet ahead of European environmental norms, and the 3^rd engine generation complies with EURO V legislation. Ethanol consumption tests in São Paulo, comparing with similar diesel vehicles, confirmed the energy content relation of the fuels.

The economic feasibility of the application requires incentives that acknowledge the alternative’s environmental benefits, given that the cost of the imported additive represents R$ 0.40/l of the end fuel price. G. Ebeling, of MWM, recalled the solutions developed in the 80’s to replace diesel oil with ethanol. The double injection system of the MWM PID D229-4 engine and the Otto cycle Perkins AE 4.236 engine converted from a diesel engine were especially praised.

Next, current developments were presented, as based on the following technologies: diesel-ethanol and the “ottolization” of the diesel engine. In the first alternative, applied to the P4001 engine, the original engine receives an ethanol injection system installed at the admission inlets, while maintaining the possibility of running only on diesel.

The quantity of ethanol injected is controlled electronically, resulting in the partial replacement of diesel oil (30 - 50%). The second alternative is being applied to the D229-4 engine and consists of reducing the engine compression rate by changing pistons, replacing the diesel oil injection system in the combustion chamber (high pressure) with a system at the admission inlets, adapting the spark plugs and introducing the butterfly throttle valve and electronic controls of spark-ignition engines.

This allows fully replacing low complexity diesel oil, resulting in a lower engine cost, but implies an increase in energy consumption. J. Medeiros, of FPT, recalled Fiat’s innovative stance from when the first ethanol car was launched in 1979, until the introduction of flex engines in 2003. He mentioned the partnership with Bosch to develop the diesel-ethanol system and said that FPT is developing an Otto cycle engine for ethanol.

The “ottolized” version will have a turbo with intercooler and multipoint injection and a 3-way catalyzer. In summary, price relations between diesel oil and gasoline, as well as their likely evolution, indicate that the replacement of diesel oil by ethanol has a more favorable potential than simply introducing ethanol. This potential must stay positive, even with ethanol prices close to the energy equilibrium price for gasoline C.

Although the automotive industry is developing technological solutions, it is important to accelerate this process by further involving the sugar and alcohol industry, also using its purchasing power. The use of ethanol in urban transportation replacing diesel will depend on environmental incentives that value the reduction in the emission of pollutants.