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San Joaquin County Community Diesel Engine Emission Control Technologies .� Development Department With regard to estimating average exhaust temperature in actual use,commonly documented engine characteristics such as the exhaust temperature at peak power and peak torque are insufficient. The exhaust temperature at the DPF's inlet is highly application dependent,in that the particular duty cycle experienced plays a prominent role,as do heat losses in the exhaust system. Very vehicle-specific characteristics enter the heat loss equation,such as the length of piping exhaust must travel through before it reaches the DPF. Lower average exhaust temperatures can also be the result of operating vehicles with engines that are oversized for the application,as one DPF manufacturer has pointed out. Time and resource requirements aside,the only way to have"foolproof' verification is therefore to evaluate a passive DPF on each individual vehicle in its own specific application. Of course, such an approach is more time- consuming and resources-intensive than is practical. That responsibility must be left to the emission control system suppliers and their customers. Staff does not presume that the proposed verification procedure will guarantee success,but rather that it will establish a high level of confidence that a given strategy will give real and durable emission reductions in compatible applications. ` Passive DPFs have the intrinsic problem that if they do not match the application well and do not regenerate adequately,they can plug up,causing excessive backpressure on the engine. Excessive backpressure can cause the engine to stall, thereby terminating vehicle operation. To address this concem,the procedure requires that DPFs be installed with backpressure monitors that will alert the operator when the backpressure exceeds some pre-set level. With some �. insight into the state of the DPF,the operator can avoid potentially costly failures. Even when regenerating properly,adding a DPF to the exhaust system of a vehicle will increase the backpressure by some amount. If more work is required from the engine to push combusted gases out through the exhaust system, a fuel ` economy penalty can result. The procedure requires that the manufacturer demonstrate that the backpressure caused by its product is within the engine manufacturer's specified limits,and if it is not,that it will nevertheless not cause any damage to the engine. It is noted in passing that test data received from the two verified passive DPF manufacturers show no discernible fuel economy penalty. Active Diesel Particulate Filters Unlike passive DPFs, active DPFs use a source of energy beyond the heat in the cxbaust stream itself to help regeneration. Active DPF systems can be regenerated electrically, with fuel burners,with microwaves,or with the aid of ` additional fuel injection to increase exhaust gas temperature. Some active DPFs induce regeneration automatically on-board the vehicle or equipment when a specified backpressure is reached. Others simply indicate to the operator when regeneration is needed, and require the operator to initiate the regeneration process. Some active systems collect and store diesel PM over the course of a r DeSilva Gates Quarry Project Draft Environmental Impact Report L-3 As osias.oe r